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Unread 02-27-2008, 10:46 PM   #1
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Question Another backer board series

I have a bit of confusion about installing backer board and needs some help. My story is that I'm working to remodel a 30 year old bathroom shower/tub stall. The bathroom itself is in great condition besides being very out of style. The existing walls have drywall with some type of backer board and then tile on top. So, here are my questions:

1) The current shower/tub stall has SBU with 5/8" drywall behind it. It seems that current recommendations are to put CBU directly up against the studs(with moisture barrier). This would leave a 5/8" gap where the drywall was located. Any suggestions on how to overcome this?

2) At the edge of the shower/tub stall the wall transitions to a painted wall. The backer board or backer/drywall combo have a different thickness than the existing 5/8 drywall. Would the experts install an extra stub to force the backer->drywall transition to be located beneath the edge of the outermost tile?

3) Ditra install instructions seem to indicate the 1 1/4" required thickness that I've been reading so much about is less of a requirement with their product. I think they had something like 5/8" listed as the minimum. Is the general opinion that this 5/8" requirement is the bare minimum to make it outside the warranty? I'm just trying to understand what I'm missing. For reference, i have 2x10 studs with 16" spacing and 10' length getting a deflecto score of L / 1020. Note that I'm ok with going to 1 1/4" and plan to do so anyway.

Thanks for you help
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Unread 02-27-2008, 11:06 PM   #2
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Hi there, welcome! Gotta first name we can use? You can fur the wall out 5/8" then put the CBU on.

You can feather the edge with some thinset and tile over it

Ditra has to go over a minimum of 5/8" ply for tile and a double layer equaling 1 1/8" minimum for stone.
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Unread 02-27-2008, 11:33 PM   #3
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Thanks for the reply. My name is Jim.

I think I may have explained the first problem somewhat poorly. The existing stall is:
stud->5/8"drywall->1/2" CBU->tile/tub

If I take the drywall and CBU down and replace it with CBU only the wall thickness would effectively shrink by about 5/8". My concern is that there would then be a gap between the new tile and tub.

I haven't actually ripped out the existing tile yet(wanted a plan first). Therefore, I'm not 100% sure there would be any gap at all. The info I have on the existing drywall+CBU is from removing the spigot cover plate and peering beneath. I suppose that my answer depends on whether the drywall runs down the wall outside the tub or tub cuts into the plane of the drywall.

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Unread 02-28-2008, 10:28 AM   #4
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Another oddball question

My kitchen is just below the bathroom in question. At some point in the near future, I have a project to remove the drop ceiling in the kitchen. This will inevitably result in some banging on the joists below the bathroom to remove drop ceiling, put in new lighting and hang some new drywall. I'm thinking that this may cause some problems like loosened tiles or at least some cracked gout. Would you agree that this is a problem or am I blowing this out of proportion?

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Unread 02-28-2008, 10:45 AM   #5
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Welcome, Jim.

MMike answered your wall question here:
You can fur the wall out 5/8" then put the CBU on.
You just fur out the stud wall with wood rips or rips of plywood so your new wallboard is flush with the old. You can also scab new studs against the old to accomplish this and plumb up the wall framing if necessary.

If you're worried about serious trauma to the house when doing the tear-out below, do it before you tile. I don't generally worry much about hurting a tile installation unless I'm tearing out the other side of the tiled wall.

My opinion; worth price charged.

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