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How much subfloor 'dip' is acceptable?

9235 Views 3 Replies 3 Participants Last post by  RDS
Sorry if this has been covered in other threads -- I can't find it.

In my bathroom, currently under DIY remodel, I've got new 3/4" plywood on top of 16" o.c. 2x10 joists, with the longest unsupported joist span only 5 feet. (Not sure if any of that is relevant to my question but I thought I'd throw it in there.)

Running a long level over the finished subfloor I see there are a couple of spots where it dips 1/8". I'm wondering if that's enough to worry about. I'm planning to put in 12x12 ceramic tile.

My plumber has offered to do the tile floor and said he'd do a 'mud job', which I gather would obviate any need to worry about the dips.

But I'm also thinking of trying it myself, with 1/2" Durock as underlayment. (I know, everyone likes Kerdi, but I need the height and I've used it before, though only on walls.) If I go that route, are 1/8" dips enough of a problem that I'd have to get out the self-leveling compound and fix it before putting in the underlayment, or would the mortar in which I (gather I'm supposed to) embed the underlayment deal with that amount of 'dip' adequately?

I'm probably being exessively anal but I want to make sure. After all this work I'll kill myself if the tile cracks because of voids under the underlayment.

Thanks for help.
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The industry spec for in-plane floors is: "Within 1/4" in 10 ft. AND 1/16" in 12" of the required plane. Since you know you have an 1/8" valley, why not fix it?

Your subfloor framing is very good and 3/4" ply is good enough for tiles. Remember 1/2" Durock does nothing extra for the floor's strength. You could end up at close to the same height, but have a better floor if you add 3/8" ply, then 1/4" cement backer. Or if you could find Ditra, use it instead of the board and have an even better floor.

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