Repairing a Damaged Pressboard Subfloor

Slide a nail puller's head under one of the nails holding the damaged area of the pressboard subfloor against the floor joists, using a hammer to force the puller's head between the subfloor and the nail's head. Pull the nail out of the subfloor, using the nail puller for leverage. Repeat this procedure for each nail on both sides of the pressboard's damaged area. Pressboard installers place nails every 6 to 8 inches along the center of each floor joist.

Cut the pressboard subfloor along the floor joists with a circular saw, using the nail holes in the pressboard as a cutting guide.

Place a framing square on the subfloor between the damaged pressboard's two floor truss cuts. Position the framing square at one end of the floor joist cuts and draw a pencil line between the two floor joist cuts, using the framing square as a guide. Repeat this procedure at the other end of the floor joist cuts.

Cut the pressboard subfloor between the floor joist cuts at one end of the damaged area with the circular saw, using the pencil line as a guide. Repeat this at the other end of the damaged area.

Lift the section of damaged pressboard subfloor from the floor joists and set the damaged pressboard on a new sheet of pressboard. Trace the outline of the damaged pressboard on the new sheet's surface, using a pencil. Discard the old pressboard.

Cut the new pressboard with the circular saw, following the old pressboard's outline.

Run a 3/8-inch-wide bead of construction adhesive across the top of both floor trusses, using a caulking gun to apply the adhesive. The construction adhesive will prevent the pressboard patch from squeaking when walked on.

Set the cut piece of pressboard in its spot on the subfloor. Step on the pressboard patch, forcing its sides into the construction adhesive. The excess adhesive will fill the gap between the pressboard patch and the subfloor.

Secure the pressboard patch to the floor trusses with 1-1/2-inch coarse-thread drywall screws, using an electric drill to tighten the screws. Place a screw every 6 to 8 inches along both trusses.