How to Level a Wood Floor
Leveling the subfloor is a prerequisite for most floor covering installations, including hardwood, laminate and vinyl. Even slight humps and depressions in plywood or OSB subfloor can mar a vinyl floor and can cause all kinds of problems with hardwood and laminate -- gaps can form, and boards can squeak and even crack. The main tool you need to level a wood subfloor is a straightedge at least 6 feet long -- a straight two-by-four works well for this purpose.
Secure all the plywood or OSB sheets to the joists with 2-inch, coarse-thread screws, even if they are already nailed. Screws are more reliable than nails and won't pop out.
Vacuum the floor and look for the highest spot. Place one end of a 6-foot straightedge on that spot and, using it as a pivot, rotate the straightedge in a circle. Mark all depressions with a pencil. If a depression is more than 3/8 inches deep, mark it as such.
Move the straightedge to another high point and repeat the procedure. Continue doing this until you've covered the entire floor.
Fill depressions deeper than 3/8 inches with roofing shingles, stacking as many as necessary to bring the floor level. Drive one or two screws into them to hold them down. You don't need to screw the shingles down if you're installing a hardwood floor; the flooring cleats will hold them in place.
Use floor-leveling compound to fill shallow depressions. It comes as a powder that you mix with water; once mixed, it sets quickly. Prepare only as much as you can use in about 10 minutes, and apply it with a drywall knife. If you overfill a depression, you can sand down the compound after it sets.
Sand down high spots in the floor with a belt sander and a 60-grit belt. Use the sander to take down excess leveling compound as well as to level mismatched joints between sheets of plywood or OSB.
Vacuum the floor thoroughly before installing the underlayment for the floor covering.
- If you're installing hardwood and you have floor sanders handy, use an edger to sand down the subfloor. It works more quickly than a belt sander.
- When using leveling compound, clean your tools and bucket with water before the compound sets. If you wait until after, it becomes difficult to remove.
Chris Deziel has a bachelor's degree in physics and a master's degree in humanities. Besides having an abiding interest in popular science, Deziel has been active in the building and home design trades since 1975. As a landscape builder, he helped establish two gardening companies.
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