Repairing Subfloors

A solid, securely fastened subfloor minimizes floor movement and squeaks. It also ensures that your new floor covering will last a long time.

After removing the old underlayment, inspect the subfloor for loose seams, moisture damage, cracks, and other flaws. If your subfloor is made of dimension lumber rather than plywood, you can use plywood to patch damaged sections. If the plywood patch doesn't reach the height of the subfloor, use floor leveler to raise its surface to match the surrounding area.

Floor leveler is used to fill in dips and low spots in plywood subfloors. Mix the leveler according to the manufacturers directions, adding a latex or acrylic additive for added strength.

How to Apply Floor Leveler

1. Mix the leveler according to the manufacturer's directions, then spread it onto the subfloor using a finishing trowel. Build up the leveler in thin layers to avoid overfilling the area, allowing each layer to dry before applying the next.
2. Use a straightedge to make sure the filled area Is level with the surrounding area. If necessary, apply more leveler. Allow the leveler to dry, then shave off any ridges with the edge of a trowel, or if necessary, sand it smooth.

How to Replace a Section of Subfloor

1. Use a framing square to mark a rectangle around the damage, making sure two sides of the rectangle are centered over floor joists. Remove nails along the lines, using a cat's paw. Make the cuts using a circular saw adjusted so the blade cuts through the sub- floor only. Use a chisel to complete cuts near walls.
2. Remove the damaged section, then nail two 2 x 4 blocks between the joists, centered under the cut edges for added support. If possible, end-nail the blocks from below. Otherwise, toe-nail them from above, using l0d nails.
3. Measure the cut-out section, then cut a patch to fit. Use material that's the same thickness as the original subfloor. Fasten the patch to the joists and blocks using 2' deck screws spaced about 5" apart.