Have a Merry Concrete Christmas

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

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

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

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

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

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

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

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

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

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

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

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

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.