Level subsurface prior to floor work
One of the best techniques to assure a smooth, compatible surface when installing a laminated wood floor is to use a mortar-based interior floor leveler to even out rough or cracked wood subfloors — a number of brands recommend against floating over hardwood or parquet flooring.
A floor leveler is generally designed to adhere to plywood or concrete and can be used to patch cracks, as well as fill low spots. There are a number of brands on the market, so read manufacturers’ instructions carefully. These products are generally Portland cement-based, pourable, self-leveling underlayments.
A good floor leveler sets hard in about 30 minutes and will not shrink or crack. In preparation, all dirt, dust or loose materials from the old floor need to be removed. Wood subfloors should be securely fastened with nails or screws to reduce uneven surfaces as much as possible. Chalky concrete surfaces should be thoroughly cleaned, rinsed and dried. A good floor leveler can be used on below-grade surface, with one caution: There should be no presence of moisture or continued dampness on the concrete surface.
Floor levelers are applied like premixed concrete. You only need to add water, stir and mix to a creamy blend. Many manufacturers recommend that you wet the concrete or wood substrate before application to improve adhesion and retard suction. Then pour the mixed compound directly onto the uneven or cracked surface and spread with a steel trowel. Allow 15 to 20 minutes for the mixture to set prior to finishing with the steel trowel.
The finish can be sanded when thoroughly dry. Floor levelers are also recommended for use when laying tough floors like tile, wood and carpet to offset the impact of long-term wear on the subfloor.