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I am wanting to tile my master bath.

When I pulled up the old linoleum flooring, it was particle-board. I've read nightmares about tiling over particle board so I'm planning on replacing it with plywood + cement backer.

This is the 2nd story of my house and the walls are sitting on top of the particle-board. On the exterior wall, I was planning on just cutting along the length of the wall as close as I can get to it and reinforcing the new plywood from underneath between the joists (which run perpendicular to the exterior wall).

However, on the interior wall near the toilet, there has obviously been a previous leak causing damage to the flooring under the wall and causing a gap (just over a 1/4in). The level of the floor here has definitely sunk (revealed by using a level) to this point.

The other side of this wall is another toilet in another bathroom which I do not plan on renovating (yet) since it is the only other bathroom in the house.

How do I fix this?

Gap1 GapCorner crosssectionDiagram

  • So the joists for the walls are actively supported by the particleboard? Not other 2x4s? – DarthCaniac Nov 19 '14 at 16:15
  • Is the particle board acting as subfloor? Or is there a layer of 2x6s under the particle board? – wallyk Nov 19 '14 at 16:30
  • @DarthCaniac - correct (I think). I cut a hole in the flooring (to get started tearing it up) and there is no visible cross beam/flooring seam that would be underneath where this wall is. I updated the OP with a cross section diagram. I don't know for sure that the wall studs line up with the joists underneath the flooring. – kinar Nov 19 '14 at 16:35
  • @wallyk - correct - I was hoping that the particle-board was simply underlayment for the linoleum and that I would find something underneath but when I cut through it, there is nothing. It sits directly on top of the floor joists and the walls sit on top of it. – kinar Nov 19 '14 at 16:40
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I think I would jack the wall up a tiny bit (1/16 inch), enough to slide out the particle board and slide in plywood.

Given the difficulties of jacks being in the way of the work, cut the plywood so it is only 12-16 inches wide (and 8 feet long or whatever) so the jacking support can be away from the wall.

  • This makes sense. However, how do I cut the existing particle board (that is sandwiched between the wall and the joists) to allow me to pull the existing flooring out once the wall is jacked up? Additionally, the same sheet of flooring extended into the other bathroom on the other side of the wall that I REALLY don't want to deal with right now (wife would kill me if I tear up both bathrooms in our house at the same time). – kinar Nov 19 '14 at 17:54
  • Actually, now that I think about it a bit more, I should be able to cut it from the underside since there is no support between the joists on the bottom side of the flooring. Of course I won't know for sure until I tear the rest of the flooring out to see if there are pipes/drains in the way. – kinar Nov 19 '14 at 18:14
  • @kinar: Does it extend under the wall? Cut it next to the wall, and then reach underneath and cut it with a small circular saw. At the joists, you'll probably have to chisel the last nubs out. If you were going to replace the floor in the other bathroom, doing so now would make this one a lot easier. – wallyk Nov 19 '14 at 18:15
  • agreed, doing it in 1 step would make it easier but I simply don't have the option of tearing both bathrooms apart right now. The 2nd bathroom may not get touched for a couple years down the road. Additionally, the back oth other toilet (other side of the wall) is only a few inches away from the base of the wall so I don't even have an option of taking out part of it. However, that seems to be beyond the scope of this question. Answer accepted. – kinar Nov 19 '14 at 20:43

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