release wood forms from surface of concrete?

Old 04-25-08, 08:55 AM
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release wood forms from surface of concrete?

I want to set a few decorative 4" slate tiles in a small concrete slab. The tiles will not be ready for weeks, and I'd like to pour the pad now, so my plan was to cut some 4.25" squares from 1/4" plywood, and press these into the wet mix flush with the surface. After it cures, I'll glue some little handles on the back with 15 minute epoxy and pull them out, leaving cavities to glue/grout the tiles into later.

Is this a mistake? Will the wood tend to float out of the wet mix, or other basic problems?

I planned to cut the edges with a 10 bevel to let them release. How tightly will the concrete adhere to the wood, particularly the porous edge grain? I thought I might cork on a bit of paraffin. Would some other release agent be better? Will residue interfere with the later adhesion of the tiles?

Finally, how long should the concrete cure before pulling the plugs. This is in Seattle, so average temp will be 50, roughly.

Old 04-26-08, 06:44 AM
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you can do it, set them in about the time you start trowling the concrete surface, use form release on the plywood or as an alternative use heavy coating of car wax. if you can find some 1/4 plate steel it would work better. just weld a bolt or handle to it before setting.
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