I am putting a new floor in the basement with 1/2″ styrofoam then a 1/2″ plywood on top. The plywood will be screwed (through the styrofoam) to the concrete floor. What should the spacing be for the concrete screws? We will then place another 1/2″ plywood to the first on.
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I would get a foam gun and use enerfoam or other polyurethene foam as a glue and forget about the crete screws myself. you only need to weight it in place for about 20 minutes while it kicks. Then glue and screw the two plies of plywood together with both axis of seams alternating to avoid double joints edit - use the glue foam to stick the foam sheets down too
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Edited 12/13/2008 6:20 pm ET by Piffin
You don't need to hold the strip in place for 20 Minutes. Like a subfloor glue, lay down the spray foam, put the strip/foam sheet in place and peel it right back up. Let teh air get to it for about 3-4 minutes and place it back in place. Sticks like contact cement.
If you just squish it in place and hold it in position, it takes a while for it to cure/stick.
FWIW...