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I would like to update the flooring in a carpeted room, replacing the carpet with hardwood. I've removed the carpet, carpet padding, and tack carpet strips.

Underneath the carpeting was OSB subflooring that has been damaged by pet urine, so I would like to replace one of the 4x8 OSB panels, and possibly another 4x4 piece.

I've removed all the screws but it the panels are glued down (I can see underneath the subfloor from my basement). I'm also not sure if this OSB floor is tongue-and-groove, and if I need to use a circular saw to cut a perimeter of the panels I would like to remove.

I don't plan to install the hardwood floor myself, but I'd like to be able to replace this subfloor if it's feasible. Currently the damaged OSB panels are level, so I'm somewhat worried about replacing them and making the floor un-level. Is it acceptable to sand / seal the OSB instead of replacing it to cover up the pet stains?

What's the best way to proceed from here? Can I cut the 4x8 piece down the middle, in-between the joists, and pull it up that way from the glued joists? Am I risking too much unleveling the floor?

  • attach a handle to the OSB .... put a 2X12, supported on blocks, across the OSB so that you can pull on the handle without standing on the OSB .... poke a few holes in the OSB using a nail so that air can get under the OSB .... stand on the 2x12 and pull up on the handle to see if the OSB will lift up a bit ... that should tell you if it is glued down ........... or tie a rope from the handle to the middle of a 2x4 and have a person on each end of the 2x4 lift up (the 2x12 would not be needed then) – jsotola Mar 26 '18 at 23:10
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    Answers go down there, @jsotola. – isherwood Mar 27 '18 at 1:44
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You can make your cuts about anywhere, but I'd avoid leaving thin strips from the edges of the existing sheets. Some tips:

  • Set your saw to depth by placing it on the edge of a new sheet and lowering the table until the blade protrudes 1/8" below the bottom of the sheet.
  • Consider cutting your replacement sheets first, then tracing them. This lets you cut for a perfect fit.
  • Cut down the centers of joists where you can to avoid needing to add backing below.
  • Cut between joists and across the joist bays where necessary. This generally isn't a problem.
  • Make extra cuts as needed to make removal easier.
  • Don't cut off the sheet you're standing on.

When you pull out the pieces to be removed you'll likely have strands of the sheets left behind, along with construction adhesive. Depending on how old and hard it all is, you'll need to either scrape or grind it away to bare joist. Lumps here will result in lumps later. A few gouges in the joists aren't a problem. A hammer and chisel can work well, as can a belt sander with a coarse-grit belt.

When you install the new sheets, use a 1/4" bead of construction adhesive at all points of contact. 2-1/2" gold screws work well. Place two-by backing under all floating joints, gluing and screwing as needed. You can't really overdo this step.

If you see any surface height issues, pull things apart and resolve them now. You don't want to have to do any sanding or grinding later. If you prepare carefully everything should remain nice and flat.

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