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opinions on gluing plywood to existing plank subfloor?
I've got a bathroom with a very uneven old subfloor. Its 3/4" by 6" boards, about 100 years old and cupped. There has also been rough patching done in various spots. The floor is about 8' x 8' give or take. removing/replacing the subfloor would be a giant PITA and I'm looking for a better solution.
I'd like to glue down 3/8" subfloor plywood to level and strengthen it. I'm thinking about applying subfloor adhesive with a notched trowel and pressing the new panels into it, then screwing it in place.
I'm not concerned about someone wanting to re-do the space in 20 years and cursing my name for using glue. I AM concerned about exactly half of the internet saying you shouldn't glue anything to subfloors because of expansion. I'm also concerned that the glue wouldn't do an adequate job supporting the voids over time.
Another option I'm looking into is leveling the floor with thinset or something similar, then screwing on the new panels for dimensional stability. My gut says glue would add a lot more strength though.
thoughts?
5 Answers
- 7 years ago
Glue will not support over a void, and the subfloor will continue to cup and shift over time. The person left cursing your project might be you when the plywood develops the same wave as the subfloor or the levelling compound breaks up and develops lumps and voids.
The better solution, and probably the least amount of expense and work, is replacing the subfloor. With an 8x8 room you can do it with 2 sheets of good subfloor material and be done with it without all the messing around with thinset, levelling compounds and such.
Remove 1/2 the subfloor*, check the joists to make sure they are level and not waving up and down. Apply 2x4 "sisters" to level out any sags. Then install the first sheet.
Use it as a platform and repeat the process on the other side. If you have a crawl spoace, remove the whole floor and stand on the dirt to woprk.
*Slice the boards in several places with a rotary saw set to 3/4 inch, then pry them off the joists with a pry bar. I can clear a 4x8 section in under an hour, and I'm a retired writer with tendonitis.
Source(s): Been there, done that ... several old house rehabs. - ?Lv 67 years ago
You are better off stripping the floor down to the joists. The two subfloor materials will squeak, squeal, and buckle at the seams.
It is a little more work, but it also gives you a chance to insect the joists. 100 years in a bathroom, that floor is probably water damaged. And I've seen plumbers cut half of the joist out to run the drains.
And with the additional 3/8", your doors will have to be trimmed. As well as the transition the other guy mentioned.
Take your time and do the job right. Peel up the subfloor and replace it with 3/4 T&G.
- smallbizpersonLv 77 years ago
Thin set first to fill the voids and screw the plywood to the sub-floor. Glue won't support the plywood and you will get splintering and cracking which will telegraph through to what ever floor you were planning to put on top of the plywood (tile or vinyl.)
Also, with this very thick solution, you will need transition strips (special thresholds) to avoid tripping hazards. (If you plan to sell this house, failure to have an adequate transition will be a red flag on the inspection report.)
- Anonymous7 years ago
What kind of finished floor are you putting on top.
Tar paper will stop squeeks
