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jfgrabe
Underlayment

Im going to tile my bathroom floor and the existing sub floor is 5/8 what thickness of cement board underlayment do you recommend?

HoustonRemodeler
Re: Underlayment

5/8 plywood is the bare minimum for tiling with ceramic or porcelain. If you are using a natural stone such as travertine, you'll need 1 1/4" minimum plywood.

1/4" backerboard (of any brand) will work just fine. So will Ditra.

Do your floor joists have the necessary deflection to allow for tiling? For ceramic you'll need a minimal deflection of L360 and for natural stone L720. If the floor doesn't meet the deflection requirements the tiles will pop off the floor after the grout crumbles away.

jkirk
Re: Underlayment

locally using concrete backer board doesnt have very good results.. ive seen two floors get backer board as a substrate 2 of them failed as the board is too brittle.

for plywood though houstan is correct 1 - 1/4" is the minimum thickness of a subfloor for a tile floor to do its job. this can be achieved via two layers of 5/8", or 3/4 + 1/2. any movement in the subfloor and the tiles can crack

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