How to Fix a Damaged Subfloor Under a Carpet

Subfloors consist of either plywood attached to wooden floor joists or a poured concrete slab directly on the ground. They provide a sturdy base for the home's flooring, including carpeting. If you notice weak spots in the carpet as you walk across it, the subfloor may be damaged. If this is the case, pull back the carpet and repair the subfloor to prevent uneven carpet wear or holes in the floor from developing. The process varies, depending on the subfloor material.

Gray carpet
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You will need to pull back the carpeting to perform repairs on the subfloor.

Remove the Carpet

Step 1

Remove all furnishings from the damaged subfloor area.

Step 2

Walk to the edge of the carpet and locate the shoe molding or baseboard against the wall. Insert a pry bar under the molding and pull out the nails from the floor. Work your way down the wall to pull off the entire piece of molding. Repeat the process on the side walls or at least halfway around the room.

Step 3

Put on heavy work gloves then grasp the edge of the carpet in a corner and pull it up from the underlying tack strips.

Step 4

Fold the carpet back on itself to expose the damaged subfloor. If there is carpet pad underneath, fold it back as well.

Repair Plywood Subfloors

Step 5

Put on safety glasses and cut out the damaged area of the subfloor with a circular saw. Extend the cuts over the nearest floor joist but do not cut through the joist. Set the saw depth to only 1/4-inch or the thickness of the plywood.

Step 6

Remove the damaged portion of the subfloor and measure the length and width of the hole.

Step 7

Draw an outline of the hole on a sheet of plywood with the tape measure and a pencil. Cut out the outline with the saw then place it into the floor opening so the edges rest on the floor joists.

Step 8

Insert 1-inch wood screws through the plywood over the locations of the joists to secure it in place.

Step 9

Fold the carpet pad and carpeting back into place and secure it into the tack strips by hand. Reattach the molding to the floor with finishing nails and a hammer.

Repair Concrete Subfloors

Step 10

Scrub any cracks or chips in the floor with a wire brush to detach any loose particles and smooth down any sharp broken edges.

Step 11

Vacuum up the concrete chips and dust with a shop vac to ensure the repair site is perfectly clean.

Step 12

Open a bag of powdered self-leveling compound and pour it into a 5-gallon bucket. Mix it with water, as instructed on the packaging, until it is smooth. The compound will be a thick liquid when properly mixed.

Step 13

Pour the self-leveling compound over the damaged subfloor until the depression or crack fills up. Do not spread the material since it evens out as it sets.

Step 14

Wait until the compound dries then sand it smooth with a hand grinder equipped with a coarse-grit sanding pad.

Step 15

Vacuum the area again then fold the carpet pad and carpet back into place. Press the carpet back into the tack strips firmly then reinstall the molding with finishing nails and a hammer.