Hi guys, 

I have designed some new table tops with a local mosaic artist. The artist just sent me the tops (each 200cm / 100cm) that are made out of tiles and on the back side of each there is just a 2-component glue that is slightly flexible which holds the whole thing together. Let s say they are a bit fragile now...

Overall thickness of the tiles is now about 1/2 inch now and my plan is to cast some self consolidating GFRC in the back so that overall thickness would be 1 inch. Basically ill flip the mosaic top upside down on the casting table, cut some melamine around it and cast.

I already did one top and the result is that it started warping. I have also noticed that when my GFRC mix drys it shrinks about 1mm every meter. And i guess that explains the warping. Warping happens on the longer side (200cm) as well as on the smaller side (100cm). 

I tried to water the top and added some weight on it to bring it back to flat but it just doesnt seem to work. 

These only option i have in mind for the tables to come is the following: 

- add some shims under the center of the casting table. The casting surface will have a small camber. So when the concrete dries it would still warp but will be close to flat. 

The GFRC mix i use is pretty standard. 50/50 cement and sand , w/c is 0,29 and 3 % fiber and polymer.

Could I change something in the mix to control shrinkage ? 

Would love to hear your thoughts on that one ! 


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Have you considered demolding, letting the shrinkage occur, then adding the tile? It helps to demold and set the piece on edge so the weight of the piece doesn't deflect the plain one way or another.

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