Fill cracks or major voids with wood putty or a self leveling compound.
Floor with low spot wood.
Use builder s felt or shingles stapled to the floor to fill small low spots if you.
Repair low spots in wood or concrete floors and clean them use an underlayment floor leveler or floor patch product to fix low spots in a wood or concrete subfloor.
If you are nailing the hardwood floor in place choose cementitious leveling compound that you can nail through.
An underlayment is a thin layer of material sandwiched between two other materials.
Use a mixture designed for wood subfloors.
Mix the compound as directed on the package then pour it onto the low spots in the floor.
3 set a long straightedge tool or a straight piece of 2 by 4 inch lumber.
Use deck screws or ring shank nails set into the floor joists to secure loose or squeaking pieces of wood subfloor material.