(Warning...Lengthy)

So I have a bit of a problem that I am looking to correct for future jobs.

I have successfully been making overlay tops now for about 5 years.  However I wanted to be able to offer a more traditional concrete top to my customers.  I made 3-4 samples of a new method. (new to me)  They were constructed based on how Elastocrete makes their tops.  Which is a 1/2" poured top with a 1/2" wrap down the sides.  I however did not use their products.  I used Trucrete's Slickmix, which as far as I could research sounded similar in many ways.  Self leveling, polishable after 24hrs, 7000+ psi after 30 days, fast initial set time, thicknesses from thin to thick.  Several other companies offer similar products like, Ardex SD-T, CTS Tru-set etc.

All of the samples came out great.  No problems....so I sold a bartop for a new bar being built.

It was constructed of 3 overlapping layers of 3/4" plywood via glued and screwed.  I then applied a sticky back fiberglass mesh to the plywood, followed by a troweled coat of Redgard to the height of the mesh.  That was cured overnight.  I then mixed and poured the Slickmix per instructions of 5qt water per 50lb bag.  We finished pouring about 11:30am.

The following day, which was slightly less than the 24hrs cure time, I polished and applied the first coat of primer sealer.  Let dry and applied the second coat late evening.  The next day I sanded and sealed with the third and final coat.

About a week later the owner called me and said there were a few cracks that could be seen but not felt.  I went to look at the job and it appears to be map cracks.  No crazing, just cracks mainly going from front to back of bar with an inside to outside corner crack.  My guess is shrinkage?

One step I did not do was cover with plastic as it cured overnight.

I called Trucrete for some insight and was told that there was mostly likely a chemical reaction going on between the redgard and the slickmix, and that the "outgasing" was causing the cracks and would continue to crack and literally pop.  Didn't seem logical to me, being that Redgard is used as a waterproofing membrane for shower systems that have thinset applied and the fact that Elastocrete used it with their system.  But I wouldn't know different.

Now I've seen these types of products being used on floors covering several hundred to thousands of square feet with no cracking.

Is there any thoughts to why I would be seeing this on a relatively small scale?

I have two other jobs coming up that I sold this product on, But I am really hesitant to proceed.  Again the samples came out great, So I assumed that the actual projects would be the same.

Realize this is a super long post, but am grateful for any thoughts.   

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Companies like Fishstone, Surecrete, Buddy Rhodes, Cheng... create systems that are tested and preform as expected. Trucrete is no exception, they have a system that works with their products, so when you introduce a primer (Redgard) thats not part of their line, you can only expect this to happen.

Certainly I can agree with that.  However, I am perplexed as to why the samples I made did not show signs of cracking.

When I spoke with Trucrete about using their product for countertops, they just said they hadn't personally tested it for that purpose.  Which I took as a way of waving liability.  Again another reason I did test samples.  

Brian,

My guess is shrinkage...On your small samples there wasn't the same forces of shrinkage as on the large pieces.  I'm sure there are other reasons for the cracking but thats my best guess why your smaller samples didn't crack and your larger pieces did.

Tom

Brian Sheen said:

Certainly I can agree with that.  However, I am perplexed as to why the samples I made did not show signs of cracking.

When I spoke with Trucrete about using their product for countertops, they just said they hadn't personally tested it for that purpose.  Which I took as a way of waving liability.  Again another reason I did test samples.  

Tom,

I really like the process I used on the samples and the bartop, would you have a product I could use in this manner that would perform better?

Post a couple pics of the cracking please.  I think Super-Six would be your best bet but going over wood (which expands and contracts differntly) there may be some other issues....pictures would help...Tom



Brian Sheen said:

Tom,

I really like the process I used on the samples and the bartop, would you have a product I could use in this manner that would perform better?

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