tile and substrate flex?

10 years ago

This is somewhat of a cross post but we have more practical tilers in the bathroom forum than kitchen (not to imply that kitchen backsplashes are merely decorative, but they don't see much actual wear...).

Anyway, I'm preparing to tile a kitchen counter overhang that has a little bit of flex. Currently it's 3/4 plywood installed by the cabinet maker. This is his
SOP for granite prep (although I don't know how that could actually work out). It's supported on 2 sides by cabinets. The unsupported
length is 9' x 15" deep.

I'll have to put another sheet of plywood (or is there something better?) on top to clear cabinet doors and hopefully stiffen it up some. Is an uncoupling membrane what I'd need on top of that? Could that be adequate? I don't know how much flex something like Ditra can absorb.

I know a post is what I really need but I'm not doing that. :)

Thanks!

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Comments (5)

weedyacres
10 years ago
last modified: 10 years ago
I found a tutorial online that recommends using 1/2" cement board as an underlayment.

The flex would worry me. I'd stiffen it more before tiling. Ditra doesn't absorb flex so much as decouple the wood from the tile when the wood flexes.
Fori thanked weedyacres
PRO
Creative Tile Eastern CT
10 years ago
Neither Ditra or cement board will eliminate flex. Another layer of 3/4" glued & screwed may work. That's a lot of overhang. If the braces are flexing don't tile it.
Fori thanked Creative Tile Eastern CT
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Fori
Original Author
10 years ago
Thanks all!

I know Ditra doesn't stop flex, just thought it might help reduce cracking from the flex that I fail to eliminate if that makes sense. :)

There is a space about 8" tall above the cabinet doors under the counter which should allow for placement of a sturdy corbel or something at the end. Couldn't hurt, right? (Especially since I have no plans to ever sit there. ha!)

Anyway, do I want a decoupling membrane over my second piece of plywood? Or can I skip it if I get everything nice and firm? It's supposed to be a dry area but it is a kitchen...
PRO
Creative Tile Eastern CT
10 years ago
Uncoupler not needed but won't hurt. If you go over the plywood use a quality modified thinset such as Laticrete #254
Fori thanked Creative Tile Eastern CT
Fori
Original Author
10 years ago
Thanks!