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Plywood Subfloor Repair

Getting Back on Solid Ground by Replacing OSB or Plywood

Replacing rotton plywood or OSB Subflooring

If your home has a basement or is built off the ground with post-and-pier supports, you probably have some plywood subflooring.

Moisture Leads to Plywood Subfloor Repairs

The usual culprit causing rotted plywood subflooring is water damage. Given that fact, you would expect it in your kitchen or bathroom. Do you find yourself in this unlucky position? How about repairing your plywood subflooring yourself?

Tool and Material List

Pry bar (for old tack strips if you have them)
Chalk line
Hammer
Tape measure
Utility knife
Circular saw
Chisel
Screws and/or nails
Plywood as needed
Wood putty

Remove the Current Finish Floor

In most cases the whole subfloor doesn’t need repair, only limited areas. To determine this you will have to remove your current finish floor, whether it’s sheet vinyl, carpet, or something else. It’s a great time for remodeling anyhow.

If carpet is what you have and it still has some life left, you can undo it from the tack strip and roll it up to reuse. If not, just get rid of it and the padding.

Important Step: Get Your Homeowner’s Insurance Agent Involved

Prior to doing anything further, give your homeowner’s insurance agent a call to review your situation and file an insurance claim. If you’re covered and you do the repair yourself, you’ll save all the labor costs that will they’ll pay you for.

Take Note of your Damage and Prep the Area

Now take a look at your plywood subfloor. Make a note of which areas need repair. Do a visual inspection and poke it with something sharp to test for mushy spots.

Plywood is an engineered wood product that holds up well, but too much moisture will break it down.

Everytime you find a spot, mark it with spray paint. When you've found all the bad spots that need repair, strike chalk lines so you’ll know where to cut.

The Good Old 3-4-5 Rule

Keep two things in mind: the spots marked off must be square. Use the 3-4-5 rule to ensure this. Secondly, any cut you make parallel to a floor joist must be down the nearest joist’s center line. Strike your chalk line centered on the existing nail heads.

Cut Out the Damaged Subfloor

Use an electrical circular saw to remove the damaged spots. Prior to cutting, look at the underside of your subfloor if you can, from the basement, to prevent cutting through electrical wiring or plumbing.

Set your blade cutting depth just one 1/8 inch deeper than the damaged plywood subfloor.

When you close in on a wall you’ll find that the bottom plate of your circular saw will prevent you from reaching the wall. It’s time to use your hammer and chisel.

As an alternative to hammer and chisel, an effective power tool is one of the new oscillating tools like the Rockwell SoniCrafter, Dremel Multi-Max, or Fein MultiMaster.

Replace the Damaged Plywood

Now that the bad plywood is gone you can install the new. There are two things to consider: the thickness of the existing plywood and the amount of new plywood you’ll need to buy. Plywood is sold in 4’ X 8’ sheets so you’ll need to buy a little extra to account for scrap.

When you get the new plywood home the rest is easy: taking measurements, cutting the sheets, and installing them. Drywall screws with coarse threads are good for this project.

But before you lay any plywood on the floor joists, lay down a bead of construction adhesive on the joists. Use a green building product like Bostik Home Heavy Duty Construction Adhesive.

It’s developed especially for subfloors, stair treads, and decks. Back in the day, the subfloor was simply nailed down. But the nails would soon work loose and cause squeeks. When you’re done, putty the gaps.

In years past, plywood subfloors were nailed down. The problem is that after a few years, the nails would work loose. What a pain to have to pull carpet or other finish floor to stop the squeeks! The thing to do now is to apply glue and to use screws rather than nails.

You might need to scrape or sand your old subfloor. Now it’s time to install the new finish floor and install baseboards... but that’s another project!