Hello all.

I am going to be putting ¾” x 3 ¼” solid Maple in our living room, dining room and the hallway. I have pulled up the particleboard underlayment in the hall and the subfloor is FAR from being flat. In some spots there is as much as ¾” difference within a 3 foot radius. I have read on this site about using shingles and heavy roofing felt for shims. Is that my only option here?

Would it be possible to use some glue or premixed thinset in between the sub floor and the ½” plywood I am going to lay over it? I know the premixed thinset is really more like glue than concrete, so I don’t think it would crack when nailing down the wood floor. This may help fill some voids and help the underlayment remain flat.

The plan would be to spread the glue (or thinset) out and lay the new plywood over it, pressing it into the glue, but not screwing it down until the glue has time to set up.

Sorry, thinset is NOT glue but a ceramic tile adhesive that is similar to mortar. If you are adding 1/2" plywood over your subfloors, just fill those valleys in first with asphalt roofing shingles till flat. Then cover with the 1/2" CDX. That's the way I do it. Easier and neater, IMHO.