step two: subfloor preparation
Under finished flooring, is the subfloor. It is the solid, structural floor of the house. Basements and slab houses have concrete, while main level and additional levels often have wood subfloors. For new construction houses today OSB is used. In the past various combinations of solid wood, plywood, and particle board were often used.
“Underlayment” is a layer of plywood or particle board that is installed directly over the subfloor and gives a solid, smooth, and flat surface for a floor covering. It is optimal for glued down floorings, like sheet vinyl and glued LVT/LVP.
Floor leveling patch can be used to fill minor imperfections in the subfloor. Padded carpet installed over concrete hides the condition of the concrete slab. Concrete slabs typically require some patching to smooth out. Different flooring types have different allowances for flatness.