I'm tearing down an old house and ran into something curious .... I know that's what killed the cat :eek::p Anyway, on the oldest part of the house the subfloor is oak with 3-4 layers of linoleum, then 4x4 sheets of plywood. In 1 room each plywood sheet has 2 holes cut in it, approximately 2"x5" filled with the cut out plywood [attached with 2 nails] That plywood was covered with linoleum and then waffle padding and carpet. Anyone know why the plywood keys would have been used?

Hey all.. Installed some 5/8" plywood over old plank subfloor. Obeyed the 1/8" gap rule. Had some unexpected drying shrinkage but nothing too bad. In my hall however, there is one gap that opened up to 1/4" or more smack dab in the middle of the hallway (running across). I plan on putting carpet in there, so what should I use to fill that gap? I trolled around but never found a real answer. Someone said floor leveling compound, and immediately someone else said it's too brittle and will crumble over time. Someone else said just caulk it, but wouldn't that still allow a little divot to form across the hall in the carpet over time? I'm tempted to just cut a 1/4" shim of plywood to stick in there, but figured I'd ask you guys first and see what a 'pro' might do in this situation. Also it would be nice to know proper procedure for this type of thing if it happens in different areas down the line. I really, really do not want to unscrew a whole piece, re-lay the felt, and set another one if something else can be done. (and if there is a good answer, please let me know if it would work for both under carpet and under hardwood... for future reference) Thanks guys! Brian