Creating Concrete Countertops

You Pick the New Concrete Blog Series

2012-02-02T11:18:00.000-08:00

I have been toying with this idea for a while now. The blog gets a few hundred and sometimes up to a thousand hits a day and we might just have critical mass. I have been getting questions on different mixes, techniques, etc. on a routine basis and have been answering them piecemeal. Here's what I propose, over the next month (February 2012) post a comment on the blog about explaining your biggest burning concrete countertop question. If I get enough responses I will post a poll at the end of the month to see which question warrants a more in depth look. I will then put together a testing plan and walk through a series on the blog step by step to develop the solution. I will do my best to limit the project to easily obtainable materials (Home Depot, Lowes, and the internet) and provide cost and links to everything. Here are some thoughts on focus areas but anything is game, it is only concrete so be creative.

Mold building (countertops, tables, chairs, ...)
Mix designs (low cost, high strength, ...)
Decorative (colors, finishes, ...)
Finishing (grinding, polishing, sealing, durability, ...)

2012 Concrete Happenings

2012-01-27T06:35:00.000-08:00

Here's a quick update so it doesn't look like I have fallen off the planet. On the concrete front I have been helping a neighbor prep his concrete floors for a skimstone treatment. Once it goes in I will post some pictures. The floor wasn't level and had big gaps around the slab edges that had to be filled. That's work that must be done but isn't much to look at.

I will be working on further refining the shotcrete mixes. I am rethinking some of the latex addition rates to try and get something that shoots better. After I shoot the next set of panels I will be doing another round of sealer durability tests but on polished sections. The last round had what I would consider, poor performance. All of the concrete was only a week old and hadn't been polished so the pores were very open. I have at least two large countertop projects coming up this year and they both will be sprayed.

This week has been very busy. I have been at concrete meetings in Washington DC and at the World of Concrete in Las Vegas. I was named one of the five most influential people in the concrete industry, which is pretty cool.

Should be a busy year.

Have a Merry Concrete Christmas

2011-12-08T05:34:00.001-08:00

Thanksgiving weekend I got inspired and Jerad and I worked on a Christmas wreath for the house under construction in the neighborhood. Of course, it's a green concrete wreath.

The gfrc backer mix I have been working on got a 10% saturation of green pigment. The concrete was mixed in a bucket with a drill and we used some available items for a mold.

The face was decorated with some leftover beer caps.

The Great Concrete Sealer Showdown of 2011

2011-11-23T07:03:00.001-08:00

With the first set of glass reinforced concrete countertop test panels I decided to test a bunch of different sealers to see how they did against some harsh kitchen tests. Wine, mustard, vinegar, and a hot bolt were used to test the effectiveness against normal conditions.

The test sections included:

1. Control

2. Cheng Sealer

3. Cheng Sealer + Wax

4. Cheng Siloxane

5. Cheng Siloxane + Wax

6. Wax

7. Densifier

8. Butcher Block Sealer

9. Eco Tuff

10. Eco Tuff + Acrisoy

11. Acrisoy

12. Densifier + Acrisoy

13. Seal Green

14. Penofin Verde Green Oil (one coat)

15. Penofin Verde Green Oil (Two coats)

All sealers were applied according to the manufacturer's recommendations and allowed to dry 48 hours before testing.

The first panel had the control, cheng sealer, and siloxane. The Cheng sealer is a penetrating acrylic. The Cheng sealer has a nice sheen that held up through all of the tests. Siloxane is a highly effective sealer used on exterior concrete, especially decorative. Other than the sheen from the sealer, the color was the same for these.

The second panel had the soy based products. Acrisoy is a penetrating acrylic which produces a slight sheen. The eco tuff is a penetrating soy epoxy primer for industrial floors. The eco tuff produces a darker wet look.

The third panel contains seal green, a side walk sealer and the green wood oil at one and two applications. And a hole when I stripped the forms too soon. The seal green didn't really change the color. The oil produced an oiled finish as expected.

The last panel had a lithium silicate densifier, wax, siloxane and wax, and a butcher block sealer. The butcher block sealer gave the concrete a brown, antique look.

After all sealer had been applied and allowed to dry they were tested. The tests included water, red wine, vinegar, mustard, and a hot bolt. Vinegar, red wine, and mustard are all acidic and will attack cement paste. Acid color stains use the acid to etch the concrete and allow the coloring to penetrate. So the mustard and wine will erode the paste and leave color behind. Ideally you don't want a countertop to stain every time something hits the surface. All liquids were left on for 5 hours to really soak in. Ideally you wouldn't leave red wine or mustard on your countertop overnight, but this was a worst case test. After the 5 hours I washed the surface with hot soapy water and a magic eraser.

The hot bolt is probably too severe. I used this test to get an idea of what color the sealer might turn if you put a really hot pan on the surface.

Here is the control section during testing. Clearly all of the liquids soaked into the surface. The hot bolt did leave a burn mark.

The acrylics did a good job of keeping the liquids on the surface.

The butcher block sealer also did a good job.

Here is the control panel after testing. Everything was compared against the control (upper left) performance. The water left a spot. The red wine left a dark stain. The vinegar dissolved the surface paste. The mustard dissolved the surface paste and left a yellow stain. The Cheng sealer alone had the best performance from this group (upper right). The siloxane didn't seem to do much. Wax didn't seem to help the sealer.

This is the soy based sealer panel. The acrisoy had similar performance to the Cheng sealer. The eco tuff epoxy generally had good performance too. It was discolored by the vinegar and burned by the bolt. The densifier reduced the effectiveness of the acrisoy. The acrisoy coated on top of the eco tuff didn't improve performance. Since the acrisoy is meant to penetrate, it doesn't work as well when coating over the epoxy.

Here is the wax, siloxane, densifier, butcher block sealer group. The wax, siloxane, and densifier really didn't work. Their performance was similar to the control. The butcher block sealer had good performance. The dark color helps hide staining too.

The wood oil and sidewalk sealer didn't have great performance.

I summarized the testing in the table below. Everything is compared against the control. NA means there wasn't anything to mention.

From this testing I would recommend three sealers. The two penetrating acrylic sealers did a good job (Cheng and Acrisoy) and so did the butcher block sealer. The acrylic sealers add a little sheen but don't change the concrete color. So if you want to use those, get the color you want from the dry concrete before application. The butcher block sealer is brown and will give the concrete an antique look.

First Round of Shotcrete Panels

2011-11-17T07:10:00.001-08:00

This week I got around to shooting a couple test panels with the new shotcrete setup. Like anything it is going to take a couple versions to get things just right. Glass fiber reinforced concrete (GFRC) countertops consist of a sprayed face layer followed by a fiber reinforced backer layer. The spraying gives a very uniform texture and the fiber reinforced layer allows a much thinner and lighter section.

For the trial, first a polymer modified Type S mortar mix was sprayed on thin.

Turns out it was a little too thin. I was aiming for 1/4" but ended up with something more like 1/8" or just enough to coat the mold. Especially on the sides you can still see some white.

Then a fiber reinforced backer mix was placed by hand. I did make enough material and this layer was pretty thin too. The panels turned out about a 1/4" thick. The goal in the future will be to get this up to about 3/4".

I stripped one of the molds after 8 hours just to see. The garage was cool and it wasn't strong enough. Notice the hole in the lower left panel. The rest stripped just fine at 24 hours. They don't weigh anything and are pretty strong, comparatively. For a first try things went well. The corners need more attention to reduce sand build up and everything could be thicker.

I am using these panels as an opportunity to do a head to head trial of a few different sealants. I have 12 sealants or combinations of sealants in the test. Then I am going to test for water absorption, red wine staining, mustard staining, vinegar erosion, and heat resistance using a hot bolt. The panels are pretty green yet so that test won't be until this weekend.

A couple more trials are going to be required to get the mix and spray technique just right.

Project S: Phase 2

2011-11-07T11:00:00.000-08:00

As a refresher, for Project S: Phase 1 I set out to come up with a countertop mix using Type S masonry mortar. It was a success and I placed the patio grill surround using a fiber reinforced Type S mix which was mixed by hand with a hoe.

I have a fairly large sized countertop pour coming up and have decided to roll this project into a second phase. I am going to develop a glass fiber reinforced concrete system based on masonry mortar.

Glass fiber reinforced concrete (GFRC) countertops consist of a sprayed on surface coat backed with a fiber reinforced support layer. Usually these contain latex polymers for tensile strength and shrinkage reduction. I picked up a large bore drywall hopper gun to spray on the face lift. The backer lift will contain glass fibers and regular bonding latex. Since the masonry mortar contains hydrated lime, I will include some metakaolin clay to use it up. The plan will be that everything but the fibers and metakaolin will be purchased locally and cheap. As we get closer to construction I will do some test sections to dial in the different mixtures. If I have some extra time I am planning on doing some surface coating comparisons to get a head to head idea of how each method I have tried performs.

Self Consolidating Pervious Concrete Pool Deck

2011-09-09T09:18:00.000-07:00

So between being very busy at school and studying for my professional engineering exam, I haven't done much in the way of countertops. So to keep the blog from getting too stale, here is an interesting post from a job I worked on this summer. Slip and fall is a big concern both on icy pavement and wet pavement, especially kids running around pools. I got a project to develop a pervious concrete mix to put around a pool deck at a Holiday Inn. These pictures are from a test pour done this summer. The test is in the mechanical room so there are way too many pipes under the concrete than recommended.

This was a very special mix. It has a new internal curing admixture which helps flowability and doesn't require curing under plastic. The concrete was brought in by wheelbarrow and finished by hand.

It was knocked down with a 2x4 and finished with a mag float. The pervious has fibers in it so there shouldn't be any issues with cracking.

A nice consistent surface.

There were two placement with different colors. This is a week later after pouring a bottle of water on each. It went through pretty quick.

KC Magazine Design Excellence Awards

2011-07-06T19:06:00.000-07:00

The latest project we have been up to is creating 50 design excellence awards for KC Magazine. Studio Build put together 5 maple blanks for casting into a polyurethane mold. The concrete was a version of a Type S mortar modified for high early strength. The concrete got lightly cleaned up and coated with semi-penetrating epoxy before applying the colored aluminum tags.

A few colored flower vases will get produced from the mold. The nice thing about polyurethane is that it does produce a very durable mold.

Concrete Grill Countertop

2011-06-08T05:42:00.000-07:00

The rebuild of the built-in grill for the Big Green Egg is complete. The countertop is prebagged Type S mortar with 1:1 latex to water and the equivalent of 5 pcy polypropylene fibers. It was cast grey and then slurried with a darker Portland cement latex slurry.

A cutout was cast in place for a mahogany cutting board supplied by studio build.

Drain channels were formed under the cutting board with clay and some green color was randomly placed on the mold.

Last weekend we had a party and it seemed to get the job done.

Studio Build and I just received a job to construct 50 concrete design awards. The originals are going to be constructed from wood and cast into a polyurethane mold. Stay tuned, I am going to use it as an opportunity to refine my home made mortar design.

Concrete Grill Countertop Pour

2011-05-17T05:34:00.000-07:00

Last weekend I placed the grill countertop using a fiber reinforced Type S mortar mixture. The mold had a knockout for a cutting board on the right. It is sloped to the front for drainage with some channels made from clay. The opening for the grill was split in half and wrapped with foam for easy removal.

The mix design was pretty simple, 1 bag of Type S mortar, 1 gallon of water, 1/2 gallon of latex modifier, and 5 pcy polypropylene fibers. The latex and fibers went into a bucket and then were broken apart using the mixing paddle on the drill. The water and mortar were mixed together by hand and then the latex and fibers were added.
All of those fibers gave it the consistency of wet manure. This was by far the cheapest countertop mixture I have ever tried.

The mortar was pressed into place by hand. It was very workable but needed pressing because of the fibers in the mix. I sprinkled some green dye here and there on the mold surface, just to see how it would turn out.

Finished, troweled, and resting. Since mortar isn't as strong as concrete I let everything sit 3 days before stripping the mold. Beforehand I rough ground the bottom and torched the loose fibers.

I have been impressed. The surface texture was as good as any countertop I have produced. It is curing a few more days under wet towels before a rough grind and sealer coat.

Concrete Tiki Torch Holder

2011-05-14T08:31:00.000-07:00

Placing the grill countertop with the new mortar mix went well. A full post is coming. In the meantime here is a little something cool. I had some extra mortar after placing the countertop and quickly threw together the pieces of the polyurethane tiki man mold. I really didn't do much to consolidate it and then used a piece of an old tiki torch to make a hole in the top.

The results turned out way better than I expected. It stripped from the mold easily and I am ready to start casting these in earnest. I may experiment with some acid stain and sealer.

The mortar weighs more than enough to make a steady base. The patio is going to need a bunch for the upcoming annual tiki pary. Time to get to work.

Concrete Grill Construction

2011-05-10T18:00:00.000-07:00

Last weekend we got a new grill and the old built-in needed some work. I deconstructed the existing grill and rebuilt it back for the new top. The old grill was an nonfunctional grill flat top from the 50's that got replaced with a big green egg. The bright mortar in the top three courses was what it took to get back to solid material.

Fiberboard template.
The top will have a knockout for a cutting board which is on the right side here. The cutting board area is sloped to the front to minimize ponding water. I split the knockout hole for the grill to make it easy to pull everything out. The pattern on the bottom of the cutting board area is modeling clay for some drainage. The hole for the egg is surrounded with ribbed foam to allow for the concrete to shrink without cracking.

Project S - Phase 1

2011-05-10T06:48:00.000-07:00

So the point of Project S is to investigate using a prebagged Type S masonry mortar for a concrete countertop base. This project is moving pretty quickly because I am using the selected mixture for the new grill top. Yesterday I put together a few mixtures and am using 1-day compressive strength asfor iteration.
I am going to be conservative and say 1-day values are 40% of 28-day compressive strength. Mixture variables were water-to-cement ratio and latex addition rate, things easily purchased or modified for the home do it yourselfer.
Mixture S1.0 - Standard mortar mixed per manufacturer's recommendations. That is 1/5 gallons of water per 80lb bag, resulting in a water-to-cement ratio of 0.79. This was a very workable mixture.
Mixture S1.1 - Same as above but with 1:1 water to latex. Latex bonding agent, this was Sika Latex R from Home Depot, adds tensile strength, reduces permeability, and reduces efflorescence in high lime mixtures such as mortar and block mixes. Slightly less workability but much less efflorescence.
Mixture S1.2- Same as above but only using latex. Low cost latex bonding agent sold at home improvement stores is about 7% solids/93% water. Although I didn't adjust for this, with equal parts latex replacement the water to cement ratio will drop a little.
Mixture S2.0 - Standard mortar mixture but with water dosed for a 0.60 water-to-cement ratio. This is equivalent to 1 gallon and 20 oz per bag of mortar. This was probably too stiff for a good countertop mixture.
Mixture S2.1 - Same as above with1:1 latex to water. This was even stiffer.
Mixture S3.0 - Standard mortar mixture but with water dosed for a 0.42 water-to-cement ratio. There was no way to achieve this naturally, so I used a high range water reducer. I know it isn't available, but it was a let's just see situation. This was a very workable mixture.
Mixture S3.1 - Same as above with 1:1 latex to water. This was a very workable mixture.
Results:
S1.0 - 1082 psi 1 day, 2705 psi estimate at 28-days.
S1.1 - 775 psi, 1937 psi
S1.2 - 818 psi, 2045 psi
S2.0 - 1824 psi, 4559 psi
S2.1 - 1565 psi, 3913 psi
S3.0 - 2378 psi, 5944 psi
S3.1 - 1445 psi, 3613 psi

Latex tends to entrain more air so compressive strength tends to go down. I didn't expect it to go down this much. However, the latex did smell a bit funky and may have gone bad. It previous experience 1:1 latex works well in countertops.
Looking at this data I selected S1.1 as a candidate for full-scale testing. The mix I will be using for the grill top will be hand-mixed in the garage and will take three batches of
1-80lb bag of Type S Mortar ($5.00 each)
1/2 gallon water (freeish)
1/2 gallon latex bonding agent ($12 per gallon= $6.00)
0.13 lb polypropylene fibers ($6.00 per 1.5 lb bag = $0.50, These can be purchased at local specialty concrete supply stores. One bag will go a long way)

So total cost for melamine, caulk, screws, and concrete is around $75.

Project S-Crete

2011-05-09T11:21:00.000-07:00

Lately I have not been very happy with my countertop concrete produced using prebagged 5000psi dry concrete mixtures. I have used a number of different brands and they are highly variable on aggregate gradation, coarse aggregate size, and fine aggregate angularity. For someone used to batching concrete in a laboratory, the variable is driving me crazy. I end up usually adding more water than I would like because the aggregate is dirty and one of the last pours had really large aggregate that had to be pulled out by hand. More water results in lower strength, more shrinkage, and inconsistent color. Luckily all of the last countertops have been black which is a little more forgiving. The big size aggregate (I'm talking one bag with a 3/8" top size and the next from the same brand with 1 1/2") and variable workability makes it difficult to get a really nice surface texture. I have spent too much time doing slurry fills and grinding recently.
Last weekend I got a new grill and had to modify our built-in brick grill to fit it. In the process I ended up relaying a bunch of deteriorating brick. That gave me an idea. My best concrete countertops have been placed using mortar. Buying sand and cement and weighing it out in the garage is a pain. Brick mortar comes prebagged, why not develop a countertop mix using as simple as possible products from Lowes, Home Depot, etc. Here goes Project S-Crete.
The rules are simple, create a forgiving countertop mix using Type S masonry mortar mix. Type S mortar mix contains Portland Cement, Hydrated Lime, and Fine Sand. It is designed to produce 1800 psi at 28-days using a water-to-cement ratio of around 0.80. I figure lowering that should up the strength and might make an acceptable mixture. I will be developing a series of iterative mixtures to determine one with acceptable properties. The selected mixture will be used as the top for the grill. The primary concern with using mortar for countertops is shrinkage. Hopefully lowering the w/c and possibly latex will help control any problems with cracking.
Stay tuned for updates and results.

Hyde Park Countertops Part 2

2011-02-25T05:19:00.000-08:00

Studiobuild has officially finished the Hyde Park residence. The countertops got installed with minimal damage. After they got installed I spend a weekend doing one last grout and grind session.

The surface ended up opening a large number of bugholes and for cleanliness those had to get filled.
I made up a latex grout mixture and worked it into the surface with a trowel and squeegee.

The old aluminum grinding hood ended up getting chewed up by some walking pads and I broke down and bought a new dust buddie setup. It is clear plastic, lightweight, and very easy to use.

The concrete was so dry that even wiped down the grout dried very quickly. The latex helps with shrinkage and bonding and provides some strength even if the grout dries before curing.

The finished concrete got two very thin coats of soy-based primer epoxy. The glass is scraps from the owner's jewelry making business.

This was a quikrete mixture with black granite seeded on the surface, dry black dye at 5%, cellulose fibers, and 1:1 latex modification.

Hyde Park Countertops Part 1

2011-02-12T17:45:00.000-08:00

Recently I have been consulting on a countertop job. Studiobuild is renovating a 1890's house in the Hyde park neighborhood of Kansas City. The owner has black concrete countertops in his current home and wanted them in the new home. So, I came on to coordinate placing the countertops for the new house.

Here we are with the molds setup in at the Studiobuild shop.

Damon, the owner, handled the dirty work. We used a modified quikrete mix with latex, fibers, and black dye.
Molds were standard melamine reinforced with plaster mesh.

Damon's wife makes Murano glass jewelry. He inlaid some glass rods and granite into the surface.

Jerad and Ryan of Studiobuild assisting damon's friends placing.

Mmmm, black concrete.

This kitchen had six pieces and took about 9 cubic feet of concrete.

Not a bad finished surface.

Adventures in Polyurethane Mold Building Part 2

2011-01-17T11:22:00.000-08:00

Sorry for the delay in posting. A large black concrete countertop project came up with StudioBuild, posts for that will be forthcoming.

Alright, mold is constructed. Tiki man is sealed and coated with release again. Let's get going.

Equal parts polyurethane weighed out.

Everything was going well until this point. The tiki man is hollow, so I taped everything off as best as I could. Not good enough and the polyurethane oozed into the mold. Thinking fast, I filled the tiki with lots of plastic bags to help hold back the pressure. The bucket on the top was to hold them down while everything set. In the process the tiki tilted a little.

Next day I stripped the mold and had a tiki man encased in polyurethane. This is the point when the words of wisdom on the manufacturer's website become haunting. Polyurethane is not like silicone. It sticks to everything, and I mean everything. Since I picked the most complicated shape on the planet, getting him back out was not a fun process. It took weeks of steady progress to free our tiki man from his rubber encasement.

Here is the mold separated from the tiki man, a little worse for wear but still ok. The tiki tilted during the pour and came in contact with the side of the mold so the top didn't turn out perfectly. I am going to cut the mold down an inch so everything should be fine. Thank goodness I used a very strong rubber compound because it took some serious pulling to get this sucker off.

Now for a test pour to see how he looks.

Adventures in Polyurethane Mold Building Part 1.

2010-12-14T15:48:00.000-08:00

I say adventure because I'm not sure this will turn out. Here is the bamboo tiki light I am attempting to turn into a concrete tiki light holder. I need to build a mold for the rubber (the easy part) and make the lamp water tight (the hard part).

Here we go, two part polyurethane used to make durable and reusable concrete stamps and molds. It's not cheap but if the mold turns out, I will be able to make a bunch of these to help defray the cost.
On the left the mold for the mold. On the right, the sealed tikiman. I backed the face area with masking tape and filled in the light bulb access and cord holes with molding clay.

Then I sprayed everything with a liberal shot of silicone mold release and glued them down. Per manufacturers suggestion there is 1/2inch between the mold and the tikiman. Once the polyurethane is set I will split it in two halves to remove the bamboo.

The silicone glue will have to set up at least a day before I can make a mess, I mean pour the mold.

Happenings in the Dr. Concrete World

2010-12-13T10:26:00.000-08:00

The weather has turned cold and the miscellaneous outdoor projects that have been keeping me from concrete projects are wrapped up for the year.
Looking towards next year I've got a few fun projects in the works.
1. I now have the domain Dr. Concrete so everything will be migrating to www.drconcrete.net eventually. The website will be a mishmash of different services from consulting to countertops.
2. I will be experimenting with two part polyurethane molds for a couple neat projects. I have been toying around with the idea of making some Tiki torch holders. What better than a tiki to hold them. We got a tiki light as an early Christmas present. I'm going to attempt to turn that into a mold. Don't worry, the light isn't trademarked or copyrighted so I won't get in trouble.
3. I'm teaming with again studiobuild to work on some concrete and wood trophies.
4. I'm doing a limited run of the planters to clear out the rest of the Ipe wood.
Stay tuned for more details.

Long Overdue

2010-10-27T11:56:00.000-07:00

After finishing the patio table for our party I got busy with other things and haven't done much with concrete around the house. I have been doing lots of other concrete work, so I thought I would post some pictures. I do lots of work with pervious concrete. Pervious concrete allows the water to pass through to reduce stormwater runoff.

Last month we placed some experimental pervious concrete on campus to look at a few different mixtures and curing methods. The sidewalk was a difficult location so we ended up using a bobcat.

This pervious was self-consolidating and I finished a good portion with a mag float.

The surface before finishing.
Normally we never use a bull float on pervious, but this mixture was special.

Putting a fresh joint in with a pizza cutter.

The completed section. Some of the tests included curing under plastic and leaving some open. The infiltration was between 100-250 in./hr which is acceptable in this location.

Concrete Patio Table (Part 4. Finished)

2010-06-04T06:14:00.001-07:00

Amongst many other projects, the concrete patio table is finished. The surface was polished up through 800 grit, sealed with an experimental colloidal silica topping, and then coated with the soy-epoxy. I don't know how the silica densifier and epoxy will play together. We will have to wait and see.

A shot of the bottom. Since nobody sees this I wanted some kind of texture when people put their hands underneath.
The concrete was cast right-side-up and the glass and embeds we seeded into the surface and troweled in.
I rubbed down the epoxy with fine steel wool before waxing. Stainless steel tapcons secured the concrete to the base.

Concrete Patio Table (Part 3. Grinding)

2010-05-17T05:05:00.000-07:00

The table was demolded after 2 days. I ground the surface with a diamond cup wheel to get through all the surface paste and remove any trowel or plastic marks. White and green glass pieces were broadcast in opposite arcs across the surface.
Now that the surface is flat, it will get ground through 400 grit before filling. I will wait a couple days before flipping it over and grinding the bottom.

Concrete Patio Table (Part 2. Placing Concrete)

2010-05-15T07:14:00.000-07:00

After a few more cans of spray foam and sanding, the shape was pretty close. This reminds me of building the molds for concrete canoes, although on a much smaller scale. The bottom square is the 3" mounting base. Then the table underside tapers from 2 inches thick in the middle to 1 inch at the edge. Since the foam is hard to get real smooth and with a short time frame to get this done, I lined the mold with plastic. It will either 1. look cool, or 2. need a bunch of grinding to smooth the bottom side.

I cut some tile backer steel mesh to insert into the top. This won't provide any extra strength, but will help keep any cracks tight. Like most concrete designs this hopefully shouldn't do anything and is there should cracks form.

Now is that concrete green enough for you? This is a modified version of my now standard self-consolidating mortar that has been working well. This mix is a high strength 2.5:1 sand to cement mortar at a 0.4 water to cement ratio. The concrete was produced using white cement, high range water reducer, air entrainer, and both cellulose and polypropylene fibers. The green pigment was dosed at 3% by weight of cement.

I seeded some white and forest green glass into the surface and broke down and put some Cheng fossils into the surface. With all of the fibers there will be more than a little grinding and torching to get the surface smooth.

Concrete Patio Table (Part 1.2 Mold Making)

2010-05-09T17:47:00.000-07:00

The mold forms completed and starting to fill in the taper for the base. The first layer is cheap foam. The square bottom is the 3" base and will taper to 1" to the outer edge.

I am using spray foam to create the taper. It gets sprayed, struck off, and then sanded smooth.

Concrete Patio Table (Part 1 Mold Making)

2010-05-03T05:13:00.000-07:00

This weekend I finished the second planter and started the mold for the patio table. These had about $10 in mold materials, $10 in concrete, $30 in stainless screws, and $30 in wood. I am going to use the basic mold again to make a bench or two. Since these molds were completely assembled using silicone and no screws, they can be reused over and over.

Very cool with the horsetail reeds.

The far planter has recycled glass tiles and the near planter has white and green crushed glass.

The table will be 40" round and will taper from 3" in the middle to 1" at the edges. The base is a $4 piece of floor underlayment. The sides are strips of 1/4" fiberboard. This mold will continue the screwless theme that has been working so well. Notice on the supports I put some masking tape. It holds well and makes cleanup a breeze. Just peel off and throw away.

Concrete Planter Project (4. Finished)

2010-03-28T19:03:00.001-07:00

Concrete ends with recycled glass tile scraps coated with soy-based epoxy. Scrap Ipe wood middle from a local rainscreen manufacture sealed with soybean oil.

Cutout detail for mounting the wood.

Concrete Planter Project (3. Finishing)

2010-03-19T14:50:00.000-07:00

I stripped the forms two days after placing. When I strip the forms at 1 day, even with high strength concrete, the finish isn't as good as at 2 days. It took about an hour to grind through 50, 100, 200, and 400 grits. Since these are going outside I didn't feel the need to go any smoother.

Straight out of the forms, pretty grey and boring.

The glass tile pieces after grinding.
They got sealed with the soy epoxy I used on the fiber optic buffet top. It is semi-penetrating and provides a nice wet look. The triangle-shaped holes are handles.

I am waiting on the hardware to put everything together.

Concrete Planter Project (2. Concrete)

2010-03-15T05:41:00.000-07:00

The concrete planter ends are progressing. All the joints got filled with silicone and a glass tile design was put into the front.

The mix was a quikrete 5000 base with 50% latex modifier. I used water reducer to bring the w/c to 0.4. It also had some fibers and a little bit of black pigment to make it a little darker. Here is my simple setup, complete with the bathroom scale and cat litter buckets.
I use two types of fibers. The left is a fibrillated (think fish net) polypropylene. The right is a cellulose fiber let over from making furnace filters and dusters. The little packets break up into individual fibers. Since I don't use any reinforcing steel, these will keep any cracks small. These planters won't ever be in tension so I probably don't need any fibers.

With the high range water reducer the concrete has the consistency of stiff honey. A little hand vibration and it flows. It needed to be flowable to get under the mounting lip for the wood boards.

Concrete Planter Project (1. Mold Making)

2010-03-10T06:39:00.000-08:00

The recent warmer weather has a few projects starting around the house. I am building raised beds for the garden out of ipe wood and have some extra material. I have enough extra to build a couple concrete and ipe planters. Ipe is a very hard, very dense tropical wood that makes great patio furniture.

Mold making for concrete countertops/projects has evolved recently (past 10 years). Cheng started using particle board and laminate then switched to melamine. Every project used fresh mold materials and used lots of drywall screws to keep things from moving. Lately Cheng has switched to foam boards secured with tape. Many other mold builders have switched to foam board and thick vinyl tape for lining the molds. Others have switched to fiberglass or flexible urethane molds. It turns out that most of the older style molds were over-built and wasted too much material. I have built a couple molds lately with little to no screws.

Here is one of the end molds for the concrete planter. It is basically square with knockouts to secure the wood pieces and a handle indentation. Other than a few leftover screws holding together the bottom knockout, there aren't any in this mold.

For the sides I cut the bottom melamine used for the fiber optic topic and sealed the ends with polyurethane. The mold pieces are held down with silicone caulk. Brown was on sale. The knockouts are just leftover plywood coated with polyurethane.
Instead of screwing the braces into the bottom piece and sides, they are secured with caulk too.
A couple minutes later the mold is complete. I let the caulk dry and then fill the seams. After casting the concrete everything comes apart and cleans up easily.

These ends are 4 inches tall and will be held just fine with caulk. The fireplace mold was secured with caulk because I didn't want to drill into my floor. That was 12 inches tall and didn't move at all. Using this technique I can reused my mold pieces and the bottom won't have a scratch.

It's Winter, blah!

2010-03-01T14:37:00.001-08:00

I haven't posted in a while because, well it's winter and I haven't done anything. Spring is getting close and thoughts of drinking on the patio are surfacing. One of the first projects for the new year is a table for the patio. I picked up this tulip base last year. It is going to get a green concrete top. I am toying with the idea of embedding steel and letting it rust through the surface.

Concrete that looks like, asphalt?

2009-12-09T10:26:00.000-08:00

A month or so ago Studiobuild was contacted by a Ferrari race team to make a couple trophies for their series championship. The catch was they wanted the bases made out of asphalt. Besides my aversion to asphalt, the logistics of an asphalt trophy just didn't' work. So I suggested the next best thing, a concrete base the looks like asphalt. Jerad made the mold and I went to work on the mix. I took a superpave asphalt mix design and substituted black cement paste with appropriate viscosity for the liquid binder. I even compacted them with a Marshal hammer. After coating with a high gloss sealer, the results look just like asphalt. Never thought I would imitate asphalt with concrete, but it worked quite well.

Concrete Fiber Optic Buffet Top

2009-11-23T05:58:00.000-08:00

The fiber optic buffet top got installed this weekend.

The finish ended up being a coat of the semi-penetrating soy epoxy. Since it ended up being very shiny I hit everything with some steel wool and then a coat of wax.

A couple layers of felt went down to provide some support for the fiber optic cables under the concrete.

Ooooooo

Ahhhhhhh

Sealing the Concrete Buffet Top

2009-11-20T05:29:00.000-08:00

I have been falling behind on blog posts with our house being on a homes tour, traveling, and school. Meanwhile the concrete buffet top has been sitting and waiting in the garage. Pretty much all of the finish work has been completed so it getting old didn't impact grinding. Although at this point there isn't anything you could do other than burn up pads.

Here is a shot of the crushed Murano glass in the surface. The big pieces are all back-lit with fiber optics.

My cat Portland supervising.
I haven't found a sealing method that I really like. I have tried the Cheng sealer with wax, just wax, and acyclic. None do a good job of penetrating and bringing out the color. I like the idea and durability of traditional epoxies, but they make the concrete look like plastic. I am experimenting with a soy-based eco-friendly epoxy. It is supposed to bring on the color and not make the concrete look like plastic and be UV stable. It mixes in two parts like epoxy but is really thin. There is no odor at all, which is good for inside work.

Here is the applied product. I tried a roller and a brush. It went on a little streaky and became more uniform during drying. I am going to give it a day or so before making a verdict, although so far so good.

Buffet Top Reveal

2009-10-08T05:34:00.000-07:00

The stripped buffet mold. The flowable concrete produced a very smooth texture with very few bugholes, just a couple on the edge.

The fiber optics all stayed in place. I used a razor blade to cut the fibers flush with the concrete.
Now it is curing under wet plastic before grinding.

Placing the Fiber Optic Concrete

2009-10-04T18:22:00.000-07:00

The fiber optic buffet mold has sat covered in the garage for a couple weeks due to some other more pressing things. Today I got back to it.

Finished gluing the fiber optics in.

Some of the first ones came loose. The ones in the mold were fine but the ones glued to the glass pieces came off. I used more hot glue on this round and everything seemed to hold better.

After finishing the mold I was so close, so I whipped up a batch of mortar. Regular concrete would be too stiff and hard to consolidate around the fiber optic lines. There really isn't a good way to consolidate without breaking them loose. The mortar mix I decided on was very fluid. This mix didn't require any consolidation and was self-leveling. It is pretty simple and worked very well. I will probably be using some variant of this on some future projects.

Here are the specs:

- 2.5:1 sand to cementitious materials,

- 5% metakaolin clay,

- 0.4 water-to-cement ratio,

- 1:1 latex admixture to water,

- 3 pcy cellulose microfibers,

- 1.5 pcy polypropylene fibers, and

- a ton of high-range water reducer

I have had problems in the past with the cellulose fibers not dispersing in mortar mixes due to the lack of coarse aggregate. The sand, water, and fibers mixed for 10 minutes before starting to mix the concrete. That seemed to get everything broken up correctly.

I let the mix come to level and let it hang out for an hour or so to begin setting up.

After the concrete stiffened some I was able to lay over the fiber optic lines with less chance of pulling them loose. I laid a couple boards on the mold to help keep the fiber optics pointed in the right direction. The plan is to tape them to the bottom of the mold to hold everything in place. I also lightly troweled down any bumps.

It didn't feel like a pulled any fiber optics loose, but we will have to wait and see. Since I didn't vibrate the concrete at all there may be some extra bugholes. Stay tuned.

Fiber Optic Concrete Progress

2009-09-10T19:36:00.000-07:00

The mold construction for the fiber optic bar/buffet top is coming along. I taped off the bottom, drew an abstract shape, cut out the shape, and glued in crushed glass. I almost cried while making the crushed glass out of a broken Murano glass lamp from Italy. It even had the master's signature but was unsalvagable as a lamp. The bigger pieces were glued in with a drop of epoxy and the little pieces sprinkled on after spray adhesive. What is the weird frame you ask, hold tight.

Here is the fiber optic setup. The bottom piece is the led light generator and the black encases all the fiber optics.
I bought a multi-strand setup that had small, medium, and large fibers. I cut enough to run into the cabinet and split the case open.

The bigger fibers got attached to the larger glass pieces to make them glow. I just attached them with hot glue. I will have to be careful placing the concrete, but they seem secure.

The strap is there to keep the fibers out of the way. I drilled very small holes into the white part of the mold and have been inserting the smaller fibers. This is a very time consuming process. It will be cool when finished and I can't rush otherwise the fibers will come loose.

Fiber Optic Illuminated Concrete Bar Top Project

2009-09-08T18:19:00.000-07:00

The next concrete project is underway. This is a top for a bar/buffet. The concrete will be regular grey with crushed Murano glass and fiber optics.

The mold is pretty standard construction, 3/4" melamine with caulked edges. I only had white caulk so it blends in. The dimensions are 62"x13"x2".

The shape of this piece is pretty straightforward, however I am trying a few new techniques on this one. An abstract shape was drawn on painters tape and removed. Spray glue will be used to seed the red crushed glass in this pattern. The fiber optics will be glued to the back of the crushed glass in this section so the shape will glow through the glass.

I picked up some highly recommended low VOC semi-penetrating epoxy for this top. I haven't been real happy with the sealer/wax setup and don't like the thickness of traditional epoxy. Hopefully this new type will be the answer, stay tuned.

Fireglass fireplace

2009-09-03T06:03:00.000-07:00

The fireglass in the fireplace.

Finished: White Concrete Desk Project

2009-08-23T18:16:00.000-07:00

The white concrete desk is completed and installed. The cobalt blue and green bottles with the white sand and cement really pops.

The hole for the computer cables was drilled after the desk was installed. I was concerned about the hole breaking during installation otherwise. Some minimal fitting was required to get everything to slide into place.

A completed, very cool, built-in desk.
Next Project: Illuminated bar top
The next project is going to be a bar/buffet top with crushed glass and fiber optic lighting.

Finishing the White Desk

2009-08-09T18:51:00.000-07:00

The white concrete desk was placed two weeks ago. Form were stripped after 4 or so days. Initial grouting was done at 4 days and moist cured. Initial grinding 50 and 100 grit was done at 7-days. A second thinner grout was applied with a rubber trowel. The countertop was moist cured for another 7-days until polishing. At 14 days after placing the top was polished through 1500 grit. So the full polishing scheme went 50, 100, 200, 400, 800, and 1500. I skipped 3000 grit since the sealer doesn't really stick to it. Four coats of sealer went on today. The sealer will cure for another day (it is really hot and humid in the garage right now) and will get waxed before installation.

Desk Progress

2009-08-03T11:41:00.000-07:00

The desk got one thick coat of slurry right after the forms were removed. Then the top was ground through 50 and 100 grit before applying a second much thinner coat. It will cure another week before beginning to polish. All of the glass stayed in placed and looks good.

White Concrete Desk Reveal

2009-07-30T05:22:00.000-07:00

One of the characteristics that helps lighten white cement is fine grinding, even finer than Type III high early strength cement. I will vouch for that. This countertop was hot to the touch 6 hours after placing. Good news is that it can be finished much sooner.

The desk proved difficult to strip the forms since the aggregate was glued in place. The glass stayed in placed and was well distributed across the surface. In this picture I started slurry coating the surface to fill the holes left from the curved part of the glass. In a day or so it will get a grind with 50 grit and then another slurry coat.

Placing the White Desk

2009-07-27T18:34:00.000-07:00

To get the colored glass, blue and green wine and beer bottles were soaked in water to remove the labels then crushed and rewashed. The mold was sprayed with glue to hold the glass in place.

All the ingredients, all white. Sand, cement, metakaolin, and latex.

I stripped a couple sides. It will cure under a wet towel for four days before grinding and another week before polishing.

White Desk Project

2009-07-25T15:26:00.000-07:00

Everything has been prepared for the white desk. The mold is a pretty standard construction. I had some leftover MDF so I used that and spray painted to seal the wood. The desk has a thickened front edge to cover the in-place frame.

The desk will be white concrete with crushed glass in the surface. I saved some good blue and green bottles. First they were soaked in water to remove the labels, then crushed with a hammer to the appropriate size. Beer bottles can be problematic if not cleaned properly. The sugars in the beer tend to retard the concrete set. These were washed again after crushing.
How do you make white concrete, mmm use white cement. This is a little harder to track down for the average person since Home Depot doesn't carry it. Masons and stucco guys use white cement or call your local decorative supplier. This cement and sand was donated by Mike Murry at Decorative Concrete Supply. The only real difference between white and regular Portland cement is they leave out the tetracalcium aluminoferrite. It is a small part of regular cement that doesn't really contribute to strength.

Another concern for making white concrete is the aggregate. Regular sand tends to make the white cement concrete a tanish color. You can buy pure silica sand (ash tray sand) at local suppliers. Since this is a small desk, shrinkage isn't really a concern so a mortar mix is appropriate.

The mix will be a standard mortar mix; 2.5:1 sand to cement, water-to-cement 0.40, 10% metakaolin clay, high range water reducer, viscosity modifier, latex, polypropylene fibers, cellulose fibers, and de-air entraining agent. The total batch will be 1.0 cf.

White Concrete Desk Project

2009-07-08T09:55:00.000-07:00

Since the last project was black, time to do something white. We built a closet in our guest bedroom and left room between the window and the closet for a built-in desk. The room is green with orange accents and blond birch trim. The plan is to build a white concrete countertop for the desk with exposed blue and green recycled glass.

Below is the black fireplace with the slate tile and new carpet.

Wood strips were secured to the studs to support the plywood top and eventually the concrete. There is a hole in the back right for cords. The countertop will be 1 1/2" thick and cap the front to end up flush with the wall. Truly white ground concrete is a difficult animal. First, you have to use white cement. Second, traditional aggregates have color and tend to make the concrete grey or tan, so you have to use something else. This mixture will be a mortar (no coarse aggregate) and have white cement with pure silica sand. Silica sand is often used as ashtray sand. Some metakaolin clay (a bone white SCM) will add strength. Blue and green bottles will be crushed and laid into the surface. It should produce an interesting effect.

KC Home Design Awards

2009-06-19T07:39:00.000-07:00

Here are a couple pictures of the awards I have been studiobuild with for Kansas City Home Design Magazine.

The concrete/mortar for the regular awards has a little higher paste content than normal with a little silica fume for higher strength. There is also a ton of non-chloride accelerator so we can demold them quickly. They achieve over 4000 psi in four hours.

The Ed Tanner awards are 100% crushed glass (beer bottles from my garage) with a blend of slag and fly ash. Since there is no cement, the slag was heat activated to achieve the desired strength.

KC Home Design Awards

2009-06-04T09:44:00.000-07:00

Although I can't show any pictures yet, recently I have been assisting StudioBuild making awards for the KC Home Design Magazine Design Excellence Awards. There are first, second, and third place awards in 17 residential and commercial categories such as "Outdoor Spaces." The awards are a combination of concrete and wood. A special concrete mixture was designed that achieves over 4000 psi in 4 hours and will have an ultimate strength above 20,000 psi. Since the awards are not a typical concrete shape, the ultra high strength will keep them from breaking should someone drop theirs.

Equipment Upgrade

2009-05-23T19:58:00.000-07:00

I was bursting at the seams with the old electric mixer. This week I picked up a 5 cf gas Ward gas mixer. The motor needs to be replaced but everything works and it is pretty clean. This should speed up future projects.

Fireplace Results

2009-05-17T20:23:00.000-07:00

The fireplace surround is done. It took longer than expected because I couldn't seem to get just the right black color. The concrete itself was black then I acid stained it black again. That still wasn't as jet black as I wanted so I used a couple coats of a very strong dye. Once the dye dried I sealed it with an acrylic. Since no one will be eating off of it, hopefully, the sealing materials don't have to be food-grade.Before

After, a little taller and wider and filled in that weird gap near the wall.
One layer of tile will go around the fireplace and then a stainless steel insert and fireglass.

Fireplace Surround Progress

2009-04-27T19:19:00.000-07:00

Here are the finishing steps and the current progress;

1. Strip the forms

2. Thick slurry coat to fill the large bug holes

3. Quick grind 50 grit through 200 grit (about 30 minutes)

4. Light slurry coat

5. Quick grind quick grind 200 grit through 400 grit (about 30 minutes)

6. Spot slurry as places that are still low

7. Finish grind at 400 grit (about 30 minutes)

8. Seal and wax

9. Lightly rub with steel wool to remove the shine

Really this project hasn't taken much time or money. The mold only took a few hours to build and get in place. The concrete was 6 bags of quikcrete at $4.50 each, 3 gallons of latex at $10 each, $10 worth of pigment, and about $10 for reinforcing steel. The concrete placement only took about 4 hours from buying the materials to setting up, placing, and clean up. The real cost was the dry grinding setup since most people are against wet grinding in their living rooms. Although if you are planning on two or more project, the speed and cleanliness of the dry setup is well worth the money.

Finishing the Concrete Fireplace

2009-04-24T17:41:00.000-07:00

After curing under plastic and wet towels for four days the first slurry coat was applied to fill in the largest bug holes and honeycombing. A light grind will knock down any high places. A second slurry will fill in any places that still need it.

Since there isn't a good way to wet polish concrete inside, the fireplace will be dry polished. The dry polishing setup uses a low-speed grinder with hot-pressed pads and a dust shield. This method is much faster and cleaner than the wet method.

Starting on the front corner.

Concrete Fireplace Surround Reveal

2009-04-21T19:59:00.000-07:00

After two days of curing in the mold, under plastic, and under wet towels the forms were carefully removed. As expected there were a few places that had honeycombing and need some slurry. The larger proportions make the fireplace stand out better.

Some honeycombing under the braces used to hold the mold together.

The concrete after a batch of colored slurry. The slurry was made using the same proportions of cement and pigment held together with just enough latex.

It is a little splotchy as the slurry dries. Another coat or two of slurry will be required to completely fill in all of the bug holes and honeycombing. A light grind will smooth the surface back out.

Placing the Concrete Fireplace Surround

2009-04-21T19:39:00.000-07:00

The fireplace surround had reinforcing steel mesh embedded 1-inch into the surface. Since it is such a long piece (about 7 feet) which is restrained by the existing fireplace, the steel helps prevent shrinkage cracking. Even though the carpet here will get replaced it was covered with cardboard. Integrally mixed concrete pigment will stain pretty much everything.

The setup in the garage. The fireplace took 3.3 cubic feet of concrete so two different batches were required. The mixture was a modified quikcrete mixture containing lower w/c, latex, high range water reducer, viscosity modifier, fibers, and pigment.
Same mixer as last time, still too small. Each batch was 1.65 cubic feet.

The mixture was self-consolidating to minimize honeycombing against the small gap between the mold and the fireplace.

The surface was hard-troweled and covered with plastic.

And covered with wet towels for a couple days.

Concrete Fireplace Surround

2009-04-12T19:23:00.000-07:00

The next concrete at home project is replacing this beige tile fireplace surround with a concrete one. The surround will be flat black concrete and be a little thicker and taller than the current version. Afterward the gas log will be removed and replaced with a low profile burner and crushed glass. The tile was held on with a combination of mortar and construction adhesive. Either way the underlying material is very rough and will create a great bond with the new concrete.
Pretty standard melamine construction. This mold used (2) 24"x48" pieces which cost about $20.
The new concrete will be about 1 1/2" out from the original. Because of the small clearance the concrete will have a maximum aggregate size of 3/8" to allow placement.
Since the floor is concrete and I did not want to drill into the slab, the mold has feet out from the front and back. Silicone adhesive was used to seal the mold to the concrete and glue it into place. It will be fine as long as the concrete is not vibrated too much during placement. In order to accomplish this, the concrete for this placement will be self consolidating.
Due to the upcoming volume of pieces that will be created this summer I have started modifying a prebagged quikcrete mixture for various applications. By adding additional supplementary cementitious materials, admixtures, and fibers I have created mixtures both for inside use and outside. Once the testing matrix is complete I will post the results of my research.

Finishing Up the Sink

2009-03-31T10:24:00.000-07:00

Other project have been keeping me busy so I better finish posting the pictures of the concrete sink before showing the next concrete items. After the sink was polished a semi-penetrating polymer sealer was applied to prevent unwanted stains or rings. A few coats of bees wax was applied over the sealer. This step is not really necessary and a holdover from colored concrete floors of the early 1900's that were only sealed with wax.

This picture shows the copper piece in the bottom of the sink. There was no functional reason for the copper, I just liked the look of copper patina. It is a textured copper. Since the inset and cabinet fronts will be walnut I stained the inside of the sink with walnut acid stain.

The copper patina was chemically accelerated. Although I made backsplashes to match the sink, they seemed a little heavy (visually) for the space. The backsplash ended up being tiled.

A mock-up of the removable walnut inserts.

The cabinet was notched to provide a small reveal to highlight the concrete sink.
Looking up the sink at the new backsplash.

To date the walnut inserts and cabinet fronts have not been completed. Pictures will be posted when everything is finished.

Polishing the Concrete Sink

2009-03-11T11:00:00.001-07:00

Alright, our concrete has stayed nice and moist for a few days and has gained some strength. Now comes the finishing. Finishing takes that boring looking piece and really makes it stand out. We must first distinguish finishing techniques. Concrete can be ground or polished using either wet or dry techniques.

Grinding - We consider the grinding phase when finishing young concrete (5-7 days old) with sanding grits less than 400 grit. Typically grinding is very aggressive to expose decorative aggregate or glass. At about 7-days old the concrete becomes too hard to grind and tends to go through grinding pads quickly.

Polishing - Polishing is finishing older/harder concrete with pads 400 to 1,500 or 3,000 grit. This produces the shiny glass-like surface.

Depending on the project you can have various grinding/polishing levels.

- Unground/unpolished is the concrete as is

- Ground/unpolished exposes aggregate but leaves a dull surface

- Ground/polished exposes aggregate with a shiny surface

- Unground/polished leaves the uniformly colored cream on a shiny surface without exposing any aggregate.

The sink contains no aggregate so only a light grind was applied to the surface at 5-days after casting. These are backsplash pieces with inlaid tiles. The top piece had a light grinding while the bottom shows the piece straight from the mold. Notice the ground piece has a slightly darker color. The concrete surface has high levels of calcium hydroxide (free lime) which is white. Grinding removes this layer.

After the concrete had cured an additional 5 days (10 days after casting), the polishing begins. For this project I used a wet grinding technique with a pneumatic grinder, since I have a large two cylinder air compressor. Wet-feed electric grinders are available. Wet grinding poses a few interesting logistical items. First, a constant supply of water is required. Mine was from a hose and milk jug with a few holes. Second, the water needs somewhere to go. My rolling cart allow the grinding to be done outside so the water just ran into the yard. Polishing inside requires capturing the water. These items mean that wet grinding requires some forethought on the setup. Notice the plastic lip on the table to prevent me from getting wet. Plan on wet grinding in a swimsuit, it makes a mess.The first round of grinding/polishing will open up some bug holes. These are small pockets of air which stuck to the mold when the concrete was cast. Most project for the kitchen or bathroom require a smooth surface for cleaning purposes, so the holes need to be filled. There are several colored-matched slurry kits available. These contain colored, polymer-modified cement paste (no aggregate or sand) which is used to coat the surface and fill the holes. Here is a picture of the sink after a slurry coat. The chips in the front lip of the sink were filled with this slurry. Small holes are generally filled with one application. Larger holes may require two or three slurry coats.
After the slurry coats were finished, stains can be applied. Stains consist of water or acid borne pigments which penetrate the concrete surface leaving behind a color. Since the vanity for this sink will have walnut drawers, the sides of the sink got a walnut color.

The sink was wet polished through 1,500 grit. As you see it is glass smooth and very reflective. The next project will use a dry-grinding technique.

After polishing we can consider sealing/surface protection options.

The Concrete Sink Reveal

2009-03-02T11:59:00.000-08:00

The concrete sink forms were removed after 1-day. The bottom was lightly ground to ensure a flat surface.

After carefully removing the forms, here is what the sink looks like. Like any new baby, fresh concrete items rarely look that good. The integral grey dye ensured the mixture had a uniform color. This sink has two faucets and a flat bottom that slopes to a single drain. The inset ledges are there for sliding removable countertop pieces. The bottom of the sink will be copper and will not get all that much finishing.

The piece in front is part of the matching backsplash. Since this was a mortar (no coarse aggregate only sand), cube samples were placed to determine the rate of strength gain.
Notice the front inside lip of sink. A portion of the concrete chipped and will require some filling. Some chipping is normal and can be easily repaired.
Individual tiles which match the shower surround were inlaid in both the backsplashes and the corner of the sink. The left side shows the blue foam used to hold the tile onto the mold. The right side shows the inlay after a little cleaning.

The sink will be covered with wet towels for 7-days to allow the concrete to cure. At 7-days the concrete is soft enough for initial grinding to reveal any aggregate. Since this mixture does not contain any aggregate it will only be lightly ground to make a smooth surface.

Placing the Concrete Sink

2009-02-27T16:34:00.000-08:00

One thing to remember out pouring a counter countertop is that your mold should be properly supported and level. A couple sheets of plywood over some sturdy sawhorses will do the trick. I built a rolling table with leveling adjusters.

Alright, double check that all of the materials are weighed out and ready to go. I have a mixer, but if you don't they are cheap to rent at the local hardware store.

*Important note: The mixture should be large enough for the batch of concrete you want to make. Mine was a little too small and I paid for it with poor mixing. I ended up adding more water and water reducing admixture to get things mixed.
The concrete was placed into the forms by hand being sure to press the first layer in well. That prevents air pockets on what will be the surface. A pad sander without sandpaper works well to vibrate the sides.
Since the concrete did not get mixed well, we had to pick out the clumps. Although you can not see them in the final piece, poor mixing lowers the strength and makes cracking more likely.

The foam knockouts can float up in the concrete. Some scrap wood and weights kept them in place. Concrete countertop mixtures are much stickier than regular sidewalk concrete. This is from the water reducing admixtures and the fibers. While these add strength, you must make sure the concrete is consolidated around all of the corners in the piece otherwise it will not look like what you designed.

After placing the concrete got covered with damp towels to provide moisture during initial hydration.

Then everything got wrapped in plastic and hung out for one day. The longer the concrete stays in the mold, the stronger it will be. One to four days is typical to let it cure before taking off the forms and starting the finishing process.

Concrete Countertop Mixtures

2009-02-27T15:54:00.000-08:00

There are several options for actually making the concrete for your concrete countertops.
1) Prepackage countertop mix - Buy all of the ingredients preweighed out, all you do is mix. Buddy Rhodes, Encounter, quikcrete, and regional suppliers all provide these mixtures.
2) Modified packaged mix - Buy regular outside sackcrete dry concrete and add colors and water reducers to make it work for countertops. Cheng Pro-formula is a prepackaged mixture you mix with regular 5000psi quikcrete to make a countertop. His mixture contains water reducing admixture, accelerating admixture, fibers, and color.
3) Your own recipe - With a little knowledge you can make your own.

The important aspects are workability (to get it in the forms), strength (to get it out of the forms and installed), low shrinkage (to prevent unwanted cracks), and low air content (to give a nice surface).

For the sink I developed my own mixture. Since it had very intricate shapes I replaced the coarse aggregate (gravel) with the same volume of sand. So the sink is actually mortar and not concrete, but for most people it is a fine line. Here is the testing summary for about 15 mixes I did. To speed up the process I was placing most of the iterations based on 1-day strength. *Remember concrete gets hard from a chemical reaction process called hydration. This process goes on forever. However, the majority of strength is gained in the first 28-days. Since the goal was to remove forms after 24 hrs, that's when I tested strength.

Testing Summary of 15 mixes:
Mixture 1 was standard Quikcrete proportions with sand instead of gravel, which contains about 540lbs of cement/cubic yard of concrete (pcy). The water-to-cement ratio (w/c) was 0.45. Lower water-to-cement generally means higher strength. I also included a deair-entraining admixture to make sure the surface didn't get holes.
1-day strength 2361 psi (pounds per square inch)
4-day strength 3393 psi
7-day strength 4570 psi (typical concrete is 4000 psi at 28-days so this is pretty good)

Mixture 2 took mixture 1 and increased the cement to 900 pcy, while lowering to w/c 0.30 with a high-range water reducing admixture (HRWR). It takes some special chemicals to lower the w/c while still maintaining workability.
1-day strength 7484 psi
4-day 8457 psi
7-day 10,582 psi (high strength concrete)

Mixture 3 maintained 900 lbs total cementitous, but substituted 15% metakaolin clay for cement. MKC is a fine white processed clay that lowers the permeability and lightens the color. This mixture also included a latex polymer to lower shrinkage and increase tensile strength. The flexural strength was improved by adding polypropylene fibers (think Easter grass) and cellulose fibers (think paper mache).
1-day strength 6391 psi
1-day tensile strength 793 psi

The ultimate mixture had good workability and strength with low permeability and shrinkage. Platinum color was added to give the sink a brighter concrete color.

Sink Inspiration

2009-02-20T06:08:00.000-08:00

Every project has to have some inspiration to start. The following are a collection of pictures borrowed from various internet sites (Buddy Rhodes, Cheng) that inspired my design for the seemingly strange looking concrete sink.

This vanity was the model for the one I built under the sink, from Kerf. Our vanity originally started floating from the wall. After handling the 4-inch concrete sink, the resident structural engineer strongly suggested I provide some legs. Our vanity turned out very similar to the far one in the picture, six drawers that will be finished shortly with walnut panels.

A two faucet concrete sink draining to a single drain. Due to space constraints and storage issues, we needed two faucets but could only fit in one drain.

Since the sink will be pretty much all sink and no countertop, this sliding piece over the trough inspired me to try and integrate some removable flat countertop sections.

I originally thought about having solid top pieces, the slotted top in this picture changed my mind. Our drawer fronts will be walnut and the removable top will have several slotted pieces for extra flat space.

Concrete Mold Construction

2009-02-11T06:02:00.000-08:00

We love concrete because it perfectly reproduces the form you put it in. However, that means the mold needs to be solid and smooth because grinding hardened concrete is much more difficult than fixing a poorly fitting mold. Below is a concrete design created by raised sections attached to the forms at the Portland Cement Association (PCA) headquarters.

Things to think about when putting together a mold.

1. Mold material should be rigid - When the mold (and whatever you have the mold sitting on) is constructed it needs to support the weight of the fresh concrete. If the selected mold material is not rigid enough there is a risk it may deflect when full of concrete and create a wavy surface. At standard weight concrete weight of 150 lbs/cubic foot and a 1 foot by 1 foot section that is 2 inches thick will weigh 25 lbs.

2. Mold surface should be smooth - Since the concrete will reproduce any imperfections the inside of the mold should be as smooth as possible. This is best done by using a laminated particle board or rigid plastic that have uniform surface texture and smoothness.

3. Mold materials should be easy to work with - Ideally special tools should not be required to create the mold. Particle board or plastic molds can be easily built using a circular saw and drill.

4. Material should be impermeable - Concrete contains water, when wood absorbs water it swells. Egyptians would place a small wood wedge in a stone crack then pour water over the wood. The small piece would swell and crack the large stone pieces. Concrete shrinks when it cures and wood swells when wet so to prevent unwanted cracks, make sure any wood in the mold is sealed. This is especially important if you have a wooden section inside your concrete such as a sink opening.

5. Mold should be designed so it can be disassembled when full of concrete - Remember, the mold will be filled with concrete. Construction of the mold should be done in reverse to allow deconstruction once the concrete is hard.

Commonly used materials include:

- Melamine (laminated particle board available at Home Depot or any other home improvement store),

- Plywood or particle board painted with exterior paint to prevent moisture penetration, or

- Extruded rigid plastic sections fixed to a rigid surface with double-stick tape or screws(available through the Cheng concrete on-line store)

Unless you are building a free-standing piece such as a table, a template will have to be made so the sink or countertop fits in the space. Walls are never straight and this prevents unwanted gaps between the wall and concrete piece. The template can be pretty much anything, plywood, particle board, cardboard, or thick plastic. The template below for the sink was 1/2-inch plywood strips glued together. Be sure to label the front, back, sides, and locations of any knockouts needed for faucets or sinks. The template will be inverted for mold construction, keep track of which direction is the front to prevent misplacing the openings. In this picture the bath vanity will have two sets of faucets with handles and one central drain. Later the drain was moved from the center to the right side.

A little note on design, start with something easy first THEN get more complicated. For this sink I tried incorporating many complicated aspects at once. It turned out well and will provide good learning experience for future project.

This mold construction is a pretty standard technique used by many concrete countertop makers. The Cheng concrete countertop book is a good reference for mold design and construction.

Here is a beginning of mold construction using 3/4-inch melamine particle board. The dimensions are roughly 42-inches long, 23-inches wide, and 4-inches deep. The sides are screwed to the bottom piece and into the adjacent side pieces. This sink bottom will be flat and slope to the single drain now located on the right side. So in this picture the far side will be the front and the near side the back. The piece on the right will be the low point of the sink where the drain is located.
The nearly completed mold. The sink bottom slopes to the right side. Wooden dowels wrapped in clear tape are screwed from the underside to make the space for the faucet and handles. The larger area for the faucet connections was made by wrapping 1/4-inch foam around the dowel and covering with clear tape. Home improvement stores have a wide variety of foam that work well for concrete projects.

Any exposed wood or screw heads get covered with clear tape. Joints and any wood to wood connections get sealed with silicone caulk to prevent moisture soaking into the wood. A dark colored silicone is easy to see on the white melamine.

Notice there is no rebar or wire reinforcement in this particular piece. Concrete is it's biggest volume when fresh and shrinks when it cures. Therefore concrete cracks. Cracking can be controlled by using a good concrete recipe and limiting the size of our pieces. The main purpose of reinforcement in concrete is to provide strength should the concrete crack. So for large concrete pieces or those with cantilevers reinforcement is good, for little pieces with good support reinforcement is not needed.

Concrete 101

2009-02-04T10:26:00.001-08:00

Since I am a professor I can't help but include a little education before we start on a project.

Although concrete is the most used material on earth other than water, most people even many of those in the concrete industry do not understand what it is.

- Concrete is a combination of Portland Cement, water, fine aggregate (sand), and coarse aggregate (gravel).

- Portland Cement plus water forms the glue that makes concrete hard through a chemical reaction process called hydration.

This figure shows the approximate volume of each component in concrete, provided by the Portland Cement Association (PCA).

We often include other cementitous materials in our concrete to improve the chemical reaction process. Many times these supplementary cementitious materials (SCMs) are by-products of other processes such as coal, steel, and silicon production. Other SCMS may include certain clays, volcanic ashes, and even residual ash from burning certain plants.

For the purpose of concrete countertops we are concerned with a few aspects important to producing a nice looking project that will lasts a long time.

1. Fresh concrete workability - The fresh concrete must be fluid enough to allow the concrete to fully consolidate into our mold and not have any air gaps or other unwanted voids. Too much water and the concrete will be weak and the gravel may settle out. Too little water and we can't get the concrete to take the shape of the mold. We will achieve a balance using a good recipe (mixture proportions) with help from some concrete chemical admixtures such as water reducers.

2. Strength - It has to be strong enough for us the take off the forms, grind or polish, and transport to the final location. The finished countertop also has to be strong enough for normal uses (i.e. people leaning, little kids walking, big pots of food). Our strength comes from the proper amount of cement and water and the use of certain SCMs that improve the chemistry of the hardened concrete.

3. Permeability - You may not think concrete is permeable, notice a sidewalk when it rains. Afterward the surface may be dry, but the concrete is still dark from water absorbed into the surface. This infiltration of water is generally bad for concrete because it transports bad stuff into the concrete (like salt or toothpaste) and leaches out some of our good stuff (like our color). For countertop purposes we will limit the rate water soaks into our concrete so the surface doesn't look splotchy when someone sets a sweaty glass or toothbrush on the surface. This will be accomplished through our concrete recipe and by the application of a sealer.

4. Other secondary aspects

- Color - Color comes first from our cementitious materials and then from our aggregates through grinding. Typically cement is grey so concrete is grey. If we want to produce a color first the grey must be overcome. However, we can also get white cement to let us make more vibrant colors. If the concrete is ground, aggregates are exposed. If we seed the mold with bright colored stones before placing the concrete then those can be ground and exposed. Color can also be applied by acid stains after the concrete has hardened.

- Weight - Concrete is heavy right? Concrete weight is a combination of the items in the recipe. Regular concrete weighs around 150 lbs/cubic foot because the rocks are heavy. However we can make canoes out of concrete that floats because the aggregate is lightweight. We will make some concrete benches and patio furniture out of lightweight aggregate so it is easy to move around.

Next, the first project a concrete bathroom sink.

Let's Get Rolling

2009-02-03T06:49:00.000-08:00

This blog will detail my experiences making concrete items for the home, including concrete countertops, sinks, and other items.

I have a testing lab available along with all of the latest chemical admixtures and concrete components and will post updates on the evolution of my concrete mixtures.
Although I have lots of experience with concrete, my first attempt was a sink for my bathroom remodel.

The upcoming to do list includes:
- a concrete fireplace surround, black dry polished in-place
- a concrete desk for the office, white with 100% crushed glass aggregate
- some patio furniture, hopefully produced with lightweight aggregate

What is pervious concrete? Pervious concrete is concrete designed with interconnected voids so water goes through it without running off. It is used to reduce stormwater produced in urban areas, recharge groundwater, reduce the urban heat island, and creates quieter safer pavements. Typical infiltration rate is 500-2,000 inches per hour. Compared to making this stuff, countertops are a breeze.

If anyone has suggestions on projects or topics they would like to see, let me know.