I am in the process of installing 3/8" engineered hardwood. There were vinyl tiles glued to 3/8" particle board which was nailed to 3/4" plywood. I have ripped up the tiles and particle board and plan to put down another 3/4" plywood subfloor prior to the hardwood (hardwood to be stapled to the plywood).

My question is: what is the best way to secure the 2 layers of plywood? I've been thinking to use flooring adhesive (called something like PL400 found at HD in a caulking type tube) to glue the two layers of plywood, and then use 2 1/2" or 3" deck screws to attach both layers of plywood to the joists. I would then use smaller screws (1 1/2") through-out the "field" of plywood to make sure it's nice and tight. I want to, as best I can, avoid squeaking. The previous flooring squeaked like crazy. They only used nails (and not too many) on the particle board/plywood (remove the old nails when I can?). Does my plan of attack sound good? Or is there a better way?

Also, the current plwood was laid perpendicular to the joists (16" OC). A few sheets have a bit of "give" in places, others don't (house is 40 years old). Should I replace the boards with a little give? And, should I lay the second layer of plywood in the same direction (perpendicular to the joists) or should I switch direction so that one plywood layer is perpendicular and one parallel. The hardwood would be laid perpendicular.

Thanks a lot for any suggestions!

Tom

Screw down the existing plywood, good.

Then screw down the top layer. You can glue it or use felt paper between.