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Community and Q&A

Flatten Old T&G Subfloor

pjpfeiff | Posted in General Questions on

I’m putting a bathroom on an uneven wooden tongue & groove subfloor.  The floor is both sloped (~3/4″ over 8 ft) and otherwise uneven (has local highs and lows).  There also is not a lot of headroom to spare, so I would prefer to raise it as little as possible.

What is the easiest way to flatten this subfloor?  I don’t mind if the overall slope remains, I just want it flat enough to accommodate the finish floor (probably vinyl plank).  Some thoughts I had:
(1) Put down a new layer of 1/2″ plywood. (Easy, but I imagine most of the unevenness would remain).
(2) Use a self-leveling underlayment.  Anyone have experience for the kinds not requiring lath (e.g. Ardex GS-4)?
(3) Lay out of grid of screws adjusted to proper heights to use as a screed for a for a mortar or other non-self-leveling compound.
(4) Tear out the old subfloor, sister up 2x4s with the joists to make a planar framing surface.

Which of those would be the easiest (and also get the job done)?  Does anyone have better ideas?

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  1. quinnowen | | #1

    I face this type of floor a lot in older properties. Since you are not intending to tile the floor I wouldn't be overly concerned about the strength of the existing floor (if you were tiling any give in the floor would likely cause cracked tiles/grout). Therefore I would go over the t&g with something like Zip Advantech 7/8" subfloor generously glued down with their Subfloor Adhesive which expands slightly and should fill any modest gaps created. This should get you a flat, but not level, subfloor off which to work.

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