Is Decayed Particle Board For My Garden

When replacing the flooring in our house, we found rotten spots and bubbles in the particle board subfloor. How do we repair the damage before the new flooring goes down? -Lisa

Hi Lisa,

Particle board is easily damaged by moisture and water, making it a poor choice for subflooring. Unfortunately, that hasn't stopped it from being used. The only way to repair deteriorated or rotten particle board subflooring is to remove the damaged areas. Here's how to go about it.

To remove damaged sections of particle board subflooring:

Safety: Wear an approved respirator or dust mask, safety glasses, and earphones or earplugs before cutting into a particle board subfloor; and close or cover doorways and HVAC ducts to contain dust. Particle board is often made with formaldehyde glue, and cutting it generates a lot of fine dust, so it's important to protect your lungs. Safety glasses are important, too, since you may hit unseen nails while cutting through the subfloor.
Locate Floor Joists: Determine the location of the floor joists using a stud finder or by the seams in the existing subfloor.
Mark for Cutting: Use a chalk line to mark the area to be removed, making sure the end cuts are centered over floor joists.
Cut Damaged Subfloor: Set a circular saw to the proper depth, so it cuts just through the thickness of the particle board, and make the cuts.
Remove Damaged Subfloor: Use a flat pry bar to remove the damaged particle board. Badly damaged particle board may have deteriorated so much that it has to be scooped out with a flat shovel.
Remove Nails: Pull out any remaining nails in the area where the particle board has been removed.
Cut New Subfloor: Mark a piece of plywood, that's the same thickness as the particle board, to the correct size using a chalk line or straight edge; then cut it to size.
Attach New Subfloor: Attach the new plywood subflooring to the floor joists with construction adhesive and screws.

If your time and budget allow, I would remove all the particle board subflooring and replace it with plywood. But if you feel the undamaged particle board will remain in good condition, you would only have to tear out the areas that need replacing.

If you're installing tile, put a layer of cement backer board on top of the subfloor, or use a waterproof underlayment membrane, so the tile will adhere properly.

Good luck with your project,

Danny

Further Information

How to Patch a Hole in a Wood Floor from a Furnace Grate (video)
Installing Tile Over a Wood Subfloor (article)
How to Level a Subfloor (video)
Installing Cement Backer Board on a Wood Subfloor Before Tiling (video)