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-   -   Backer board vs. plywood for tile underlayment (

allpraisebob 01-05-2007 05:59 AM

Backer board vs. plywood for tile underlayment
A friend of mine with virtually no experience decided to remodel the only bathroom in his house about a month ago (still an ongoing project, proving the advice that if you don't know what you are doing you are much better off hiring someone to do it!). It's a ~70 year old wood frame house so there was lots of termite damage in the joists and at least 4 layers of flooring that needed to be removed (3/4" pine t&g boards, mosaic tile, linoleum, and finally more tile) that all told was around 1.5" thick. I recommended he remove everything so weak joists could be sistered and new plywood decking be installed (3/4" t&g). I also recommended that he use 1/2" CDX plywood on top of the decking as underlayment for the new tile floor, as I felt that cement backer board might be too difficult for him to install properly. With the joists sistered and 1 1/4" of plywood for a subfloor, I can attest that everything feels very solid. Why, then, would the tile supplier make such a big deal about how he should have used backer board instead of the 1/2" ply as underlayment? Backer board doesn't improve the structural strength of the floor, and as far as I know, the only real improvement it offers over plywood is improved adhesion for the thinset. I do feel it is has merit in tub surrounds, but for floors I just don't see the benefit. Am I missing something??? I'd like to offer my friend a "third-party" opinion on this, even if it means I'm wrong and the tile lady is right.

Rehabber 01-05-2007 09:45 AM

The difference in expansion /contraction of ceramic tile and backerboard is similar. the difference between tile/plywood is larger and prone to failure. If you want the floor to last, strip to tonge and groove, screw down plywood to tonge and groove, then use unmodified thinset and screws (or some use nails) to put down backerboard on 3/4" plywood. Tape and thinset backerboard seams and then set tille:thumbup:

allpraisebob 01-06-2007 05:22 AM

Ok, that makes sense Rehabber. I suppose I will have to go to my friend's with hat in hand on this one. Still, using latex-modified thinset on the 1-1/4" of plywood that was screwed and glued (PL-200) together ought to be ok, right? It might not the best way of doing things, but it isn't so bad that the tile should be ripped up and re-done...

Rehabber 01-06-2007 07:15 AM

It's down now, With any luck it will be OK.

Bud Cline 01-07-2007 07:44 PM

That's an awful lot of work to complete start to finish in just over twenty-four hours, you guys are super. Are you two for hire?:)

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