If the uneven floor is due to floor joists that have warped or twisted over time or were incorrectly installed the only way to level the floor is to remove the subflooring and shim the joists.
Floor with low spot wood.
An underlayment is a thin layer of material sandwiched between two other materials.
Mix the compound as directed on the package then pour it onto the low spots in the floor.
Use a mixture designed for wood subfloors.
Use deck screws or ring shank nails set into the floor joists to secure loose or squeaking pieces of wood subfloor material.
It s used to help insulate absorb sound and reduce wear on your floor.
Fill cracks or major voids with wood putty or a self leveling compound.
If you are nailing the hardwood floor in place choose cementitious leveling compound that you can nail through.
Use builder s felt or shingles stapled to the floor to fill small low spots if you.