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rtoni 12-15-2010 04:54 PM

cement board flex (a bit)
hi - I installed a product called PermaBase from National Gypsum - got it in 4' x 8' sheets which I cut to fit my shower walls. Framing is 2x6 16" o/c. I used concrete backer board screws to attach cement board to studs. On one sheet I trimmed 12" off the long edge (the 36" remaining covers the short wall in the shower) and the other wall is the full 4x8 sheet. So the only seam is the corner which is well supported by the additional stud / framing there (both edges of the corner screwed in every 6" all the way up). Outside edges fall on center of stud. It all went on pretty easy and seemed pretty solid. I set a level across the walls / studs before screwing in on to make sure they were true.

But - when i lean against the wall directly between 2 studs about midway up the product flexes just a tiny bit. I have to push pretty hard on it but still, what's up with this? This is a full 1/2" cement backer screwed in like crazy (every 6") fastened on a nice straight wall. There should be no give, correct?

I'm thinking if I use a large tile on the wall (one which pretty much spans the distance between studs) the tile itself will stiffen things up and I'll never get this flex - nobody will walk on the wall (at least I hope not :eek:). But a smaller tile and someone pushing on the wall in the "right spot" might cause the grout to crack or worse the tile to fall off..?

I'm ok with larger tile (that was the plan anyway) - or do I just need to take this down and put a layer of ply or gyprock or something on first? Of the few installs I've seen that's never been done. I'm surprised a 1/2" concrete backer has any movement to it at all. Not sure what to do. Thanks for any advice...

Ron6519 12-16-2010 08:26 AM

Don't worry about it. I've done dozens of bathrooms with all sizes of tile and never had an issue with the flex.

rtoni 12-16-2010 03:01 PM


Originally Posted by Ron6519 (Post 551979)
Don't worry about it. I've done dozens of bathrooms with all sizes of tile and never had an issue with the flex.

Ron - can't tell you how much that sanity check is worth. I do worry too much sometimes but the times I don't worry are the ones that seem to bite me.

This job (framing and tiling a shower) is huge for me - I'm not afraid to tackle it but with lots of questions along the way.

Thanks for the reply

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