Sunday, December 2, 2012

Buffon Project Progress

The Buffon project is just about finished. Once everything is in place I will get the completed pictures.
Here is the setup for the island pour. The island is 44 inches by 12 feet. It was cast off site and carried into place.
 A cell phone shot after finishing the pour. The hollow spot in the back is the section over the cabinet, the rest is solid and overhangs.

It took 8 people but the island top is in place. The island is wrapped on both ends by solid concrete pieces. 

Tuesday, October 16, 2012

Internal Curing Concrete with Super Absorbent Polymers

In the previous post I mentioned adding a super absorbent polymer (SAP) to the mixture to improve curing and eliminate having to put plastic on the fresh concrete. I have been using SAPs for a number of years in traditional concrete and have been very happy with the results in countertops.
A little background:
Concrete gets hard through a chemical reaction called hydration. Various cement components dissolve and recombine to make concrete hard. The ultimate strength and durability is related to the cement chemistry and amount of water in the system. Lower the water-to-cement (w/c) ratio the stronger the mixture. Unfortunately the hydration products occupy a smaller volume in their hardened state than in the fresh state, so concrete shrinks. At w/c less than 0.42 this shrinkage can be significant enough to crack the concrete from within. Also at low w/c the permeability of the hydrating paste is so low that water can't get in. If you break a low w/c mixture that has been stored in water, the middle will be dry and hydration has stopped. Hey, wouldn't it be nice if we could include some extra water in the mix that the cement can use during the hydration process? Yes and in comes SAPs.
SAPs basically soak up a bunch of water, expand, and give the water back one time. They aren't like sponges and only have a single use. Since we put more water in the mix than is needed for complete cement hydration, adding a SAP to soak up the extra water will help in the long run. The other thing needed for a good SAP is a small particle size for good distribution. Baby diapers are SAPs but the polymer grains are very large and would leave big bubbles if used in concrete. The particle size of the SAP I use is designed to work well within concrete.
The version of SAP I use is called Hydromax. You can buy a 4 lb canister for about $80 which is sized for 8 cubic yards of concrete. That one container is enough for 40 or so normal sized kitchens. The dosage rate is 2 oz per 100 lbs of cementitious material in your mixture. Just throw the SAP in with the mix and proceed as normal. It will not produce any noticeable changes in the mixture. Overall these mixtures gain strength faster, have better overall strength, and less shrinkage.
One thing to note, SAPs are very fun to play with. If your kids or drunk neighbors get ahold of them you may run out from all the experiments.

Sunday, September 16, 2012

How to Avoid Bug Holes, Pin Holes, and Other Nasty Surface Imperfections in Concrete Countertops

I recently had a question about how to eliminate pin holes or what we call bug holes. Bug holes are problematic for any concrete which needs to be decorative, whether it be an architectural facade or a countertop.
What they are:
Bug holes are entrapped or entrained air pockets. Entrapped air usually comes from the placing technique when you put concrete in the mold. Entrained air is air caught up in the mixing process. The big bubbles are entrapped air. The little bubbles are usually entrained air.

What causes them:
There are really two things that cause bug holes, the placement and the mix. A third consideration is materials seeded in the surface. First, for placement the mix needs to be flowable enough that minor vibration (tapping the surface) will release the entrapped air. Some of the professionals sell and advocate vibrators. These are great but at $500+ don't make much sense. I would suggest starting at one end and pushing the air out as you progress.
Second, if the mix has lots of air in it, you will have lots of very small air bubbles. Typically high amounts of polymer/latex will cause lots of air bubbles. Various companies sell densifier or defoamer or deair-entraining admixtures to add to concrete mixtures. If you need to add these then the mix is already incorrect. I have tried several products and just have been disappointed. Deair-entrainers are materials with very high surface areas to pull out the surfactants (think soap) that cause the air. The problem is that they also reduce the workability. The integral densifiers are silane or siloxane based sealers which make the air bubbles slippery and the thought is that they escape. I have tried these products and they work much better as a sealer than an integral product unless you are looking for chloride resistance like on a bridge deck. That and a little bottle is like $75.
Third, If you put decorative aggregate on the surface of a mold there is always a small air bubble trapped between the mold and aggregate. This mold below had lots of black aggregate combined with poor consolidation to produce lots of bug holes. The amount of slurry required would turn anyone off of concrete countertops. 

How to fix them:
If your concrete is decorative then the bug holes might be interesting. Many exposed concrete building have bug holes on the face which adds texture. On your countertop the bug holes just hold food and are impossible to clean. The only way to fix bug holes is to slurry. My white concrete desk shown below had lots of glass bottles seeded into the surface. Bottles are round and unless the pieces are tiny, have a curved surface which leaves a void. All these voids need to be filled.
Step one is to lightly grind the surface to open up any holes that need filling. I like to do a wet sand with a scotch brite pad.  Notice the countertop below, a few bug holes on the top and a bunch on the side.
The next step is to slurry. Cheng and a few others sell color matched slurry. I have used Cheng's and I really liked the consistency and the color match was perfect. I could take or leave his concrete mix but the slurry was first class. That being said the consistency and application are crucial. If you look on youtube or get Cheng's DVD for slurry/finishing the consistency is something like this, very thin. This works but takes 2 or 3 coats to fill big holes. The problem is that the surface tension in something this thin will keep it from going in the little pores. You will end up just wiping it over the surface and the little holes keep showing up and laughing at you.
Here is the magic trick. I like to mix my slurry thick. Wipe down the surface so it is damp with a clean sponge and then smear the paste on with another sponge. See how it builds on the sponge, this allows you to press it in the void space. I don't care how big the bug hole is, one pass is all it takes. After you slurry there will be material built up on the surface, don't worry. Let everything sit an hour or two and come back with a wet scotch brite pad. Rub the surface down. The material will be hard enough to stay in the void but soft enough to easily be removed from the surface.
Here is a recently completed countertop placed with a light grey concrete and slurried with a dark grey. We call this honed gun metal, but it probably should be garage floor. If the slurry was color-matched then everything would be light grey. My thought is that if you want one perfect color, go with laminate.
How to eliminate them:
How to eliminate bug holes, there is no perfect way. Consolidate the concrete near the surface as best you can. For a traditional mix I like to place a 1/4 inch and then really work it in with my hands. If you are going to do more than one then GFRC is the way to go. This may be for another series but spraying a face coat eliminates 90% of the bug holes. The mix has no coarse aggregate and is pretty much just fines. The consistency should be enough to easily spray through a gun but stick to a vertical surface. Here is a test shot. Stick to the surface but if you get too much it runs. I spray mine with a normal drywall hopper gun.
If you have specific questions ask. Assuming I get a chance I will try and answer what I can.

Thursday, September 13, 2012

Buffon Residence Progress: New Frontiers in Concrete Countertops

The Buffon residence project is coming along. The project slowed up a bit in August because I was traveling and since the owner is months away from moving in, I can take it easy. The two larger test pieces are finished. I have been using the eco tuff epoxy for smaller pieces with success. When I put it on these pieces it just didn't look that great. Even with a foam roller it had bumps and the surface was very shiny. This kitchen has halogen spot lights which showed every smudge and bottle mark. So I embarked on a mission to bring the shine down. Unfortunately the epoxy is so hard the sanding is out of the question. So I ended up trying lots of difference sealers, again. Well, I found one I like which produces a satin finish, is easy to put on, and very durable. What is this amazing sealer, drumroooooool, regular old Spar Urethane. Yep, the same stuff you can buy at the hardware store. Funny, on the can it says countertops are one of the uses. It fits the bill, easy to apply, consistent texture, non-yellowing, and very hard. From here out two coats of satin urethane and a coat of wax will be the standard. It does also bring out the wet look color just like epoxy and has a higher heat rating than epoxy. Ok, that problem is solved and in a pretty easy manner.
They look very industrial, which while cool isn't really what I was going for. Part of the reason is that it was 95 plus when we placed these and the face set very quickly. Back, kind of, to the drawing board.

So what's the deal with new frontiers? Well I have been playing with a super absorbent polymer for eliminating curing on pavements and it works great. Think super duper baby diaper gel. This stuff will soak up 2000 times its weight in water and doesn't let go until the cement needs it. It eliminates plastic or water curing and generally improves all concrete properties. The stove section was placed last Friday, same mix as before but with the magic juice. It sat a couple days before stripping and flipping. Funny, this piece is 8 ft long and I flipped it by myself no problems. Below is a shot after flipping without any finishing. The texture was great, consistent, with very minimal bug holes. 

After a quick wet hand polish with a scotch brite pad. I won't even have to use the grinder/polisher on this piece. All it will take is a hand scrubbing, slurry, and a second hand scrubbing before sealing. 

Seems like this will work. Each of the remaining pieces will be completed probably one per week due to space constraints. Stay tuned. If you have questions on the specifics let me know.

Thursday, August 2, 2012

StudioBuild Buffon Residence: Part 2

The StudioBuild Buffon residence project is underway. Unfortunately the mixing paddle broke on the first spray coat and by the time we got a new one from the hardware store it had been mixed too long. I ended up shooting a face coat that was way too wet and kept clogging in the gun. We stripped the forms, polished and fill any holes, but it just wasn't perfect. So here is take two.
This is a dark grey GFRC countertop. The face coat is sprayed and the backer coat is hand packed. The face mix uses Type S mortar, portland cement, and latex from home depot/lowes. The face coat also uses black pigment from the local decorative concrete store, high range water reducer which you can get on the internet, and metakaolin clay also found on the internet. The backer mix only uses Type S mortar, portland cement, latex, glass fibers, and water reducer.
The nice thing about the GFRC mixes is that they aren't full depth so you can fill the mold with water during curing.

The fresh concrete is placed over the side of the forms and then ground off flush after 1 day.

This is not the best picture, but here is the top. The white swirls are the paste wax we used as form release. After curing wet under plastic for 7 days, it will get a light polish 400-1800 grit before sealing.

Monday, July 23, 2012

Studio Build: Buffon Residence Part 1

The next project is concrete countertops for a StudioBuild house renovation. Sorry for the bad cellphone pictures, I will get some better ones soon. The kitchen has a large run along the wall, an island with a cantilever section, and an upper section on the pass through to the living room. The mix is dark grey gfrc with a sprayed face and hand packed backer coat. 

This is the first of many molds. There are two pass through pieces with cutouts for columns. The melamine sides were glued to the base with silicone and supported with blocks tacked into the base. We will be reusing these for the full-width sections.
Yesterday we shot the first section to work out the kinks and will be getting ready for some full production soon. 

Tuesday, April 10, 2012

Concrete Updates

I have been light on posts the last couple months not because there is too little going on. It's completely the opposite, the big concrete jobs have been keeping from the little fun ones.
Here are a couple pictures of some on-going big projects.
The first full-scale photocatalytic pavement section is under construction on MO61 in St. Louis. This is cement technology originally developed as self-cleaning concrete for a white church in Rome. Since then we have learned it is also smog eating. The mainline section is two-lift smog eating concrete and we are installing photocatalytic pervious concrete shoulders too, pretty cool.

Here is an example from left to right of the self cleaning ability when submitted to sun for a couple hours a day.
I have slowly been refining the mix for shotcrete countertop panels and have a very good system in place. Other than high range water reducer, glass fibers, and metakaolin clay, everything else comes from home depot. That means for a normal kitchen countertop installation I will be in less than $200 in materials.
On a related note, a few weeks ago I received the American Concrete Institute's Walter P. Moore Jr., Faculty Achievement Award.

Thursday, February 2, 2012

You Pick the New Concrete Blog Series

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, ...)

Friday, January 27, 2012

2012 Concrete Happenings

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.