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Unread 09-29-2021, 08:47 PM   #1
Lala888
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Waterproofing outside of curb

Hi! I know that it’s not as good as lathe and mud, but my tile guy went the CBU route to build our shower curb. He then used fiberglass mesh tape and aquadefense to waterproof the top and sides, but left the back totally open. I’m not 100% comfortable with that.
Could I just apply a sheet membrane over this whole curb, extending onto the CBU that I plan to put on top of the plywood floor? Thanks for your help!!
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Unread 09-29-2021, 09:09 PM   #2
cx
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Welcome, Laura.

Not only is it "not as good as lath and mud," but it's wholly unacceptable. It's been said many times on these forums, but is apparently worth repeating here: There is no acceptable method of using CBU on the curb of a traditional shower receptor. None.

What your contractor has done, apparently out of ignorance of his trade, is not acceptable. His effort to waterproof the mechanical fastener penetrations through the waterpoof receptor liner simply will not work in the long term. Water will wick up into the CBU on the inside face and the top of the curb and will work its way through the holes he made in the liner.

The manufacturer of the waterproof liner, the residential building code, as well as the ceramic tile industry standards, require that no penetration be made in the waterproof liner below a line six inches above the shower floor or two inches above the top of the curb, whichever is higher.

Do you have fastener penetrations below that line at other places in the shower?

As for the outside of the curb, that would be considered outside the wet area and is not required to be waterproofed. The waterproof liner is frequently run over the curb and fastened only to that outside face. You could, if you wanted, use a direct bonded waterproofing membrane on that outside face of the curb and onto the floor if you think it would help with water that splashes out of the shower opening. It's not an industry requirement.

You are paying for a properly constructed shower. You're currently not getting one. Do you have a written contract for this shower construction?

My opinion; worth price charged.
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Unread 10-01-2021, 02:14 PM   #3
John Bridge
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Hi Laura,

I agree with what CX said. It's not acceptable. It'll leak for sure.
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Unread 10-01-2021, 03:01 PM   #4
Lala888
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Oh no!! I stupidly didn’t get a contract, and I’m a conflict-avoidant wimp. I planned to lay the tile myself, and I already paid him just to build and waterproof. I was satisfied until I started studying here to learn about how to do the tile. From what I’ve read, I at least feel good that he did the floor right (preslope then liner).

Do y’all think there’s any way I could fix the curb myself? Like put a sheet membrane and fabric corners over it?
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Unread 10-01-2021, 03:06 PM   #5
Lazarus
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If that is cement board, it can be covered with Kerdi and will be waterproof. 2x4's cannot be covered with a waterproof membrane......
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Unread 10-01-2021, 03:26 PM   #6
Davy
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I doubt you want to start over with a new pan liner so at this point I'd remove the CBU from the curb and patch the holes in the liner. Then wrap it in lath and mud it like it should have been done in the beginning. That way the top of the curb would have pitch towards the drain.
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Unread 10-01-2021, 04:25 PM   #7
Lala888
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Davy, I’m afraid I don’t have the skill to do mud myself! Laz, it’s Durock covering 2x4s and liner, “waterproofed” with Aqua Defense and fiberglass tape. Should the thinset bond to that?
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Unread 10-01-2021, 05:51 PM   #8
jadnashua
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Thinset will bond to Aquadefense, but that's not your problem!

Neither tile nor thinset nor cbu are waterproof...they're water resistant, and not (generally) damaged by being wet. The edges of the cbu are either touching or sitting in the mudbed, so they will wick moisture from that edge (and behind, as water will try to move from wet to dry areas).

In a conventional shower liner build, the liner wraps around/across the curb, then down the outside, and is only fastened on the outside. To make the cut so you can fold the liner over the curb, you must install the special curb corners.

At this point, if you can't mud the curb, you could probably remove the cbu, use the proper cement and patches of the liner material to seal the holes, then, if it's sized properly, they do sell a foam, wrap-around curb that can then be tiled. This is one possibility. https://finpan.com/products/accessories/curb-overlays/

I've not used this, so can't say how well they work. The stack of 2x4 must be per the design, otherwise, there'd be nothing to support the foam cap.
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Unread 10-01-2021, 08:13 PM   #9
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The Noble Company also makes a foam curb overlay that is intended to replace the lath and mortar of a traditional shower receptor construction. Whole lot more expensive than lath and mortar, but possibly something that will fit your need.

My opinion; worth price charged.
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Unread 10-02-2021, 09:57 AM   #10
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Used to use the overlays a decade or two ago. They work well and solve the waterproofing problem if used over 2x4's...a bit pricy and I prefer brick or block if on a slab.
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Unread 10-02-2021, 09:44 PM   #11
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Are the overlay curbs made with a pitch?
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Unread 10-02-2021, 09:53 PM   #12
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I don't think so, Davy, but the Noble instructions do tell you to install them with appropriate slope to drain. And they are meant to be mechanically fastened to the outside of the curb, so I can see pitching them shouldn't be a big problem.

But I've never actually installed one.
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Unread 10-02-2021, 09:57 PM   #13
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So, making a pitch is done how? By tilting it? Or is there enough flex in the foam to force it to slope?
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Unread 10-02-2021, 10:05 PM   #14
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I expect so. I have one in the shop and they're clearly too rigid to allow them to slope any other way. Indeed, I'm not entirely sure a fella can get a substantial slope fastening only to the outside surface and having the rest just filled with thinset mortar. I guess I should actually try it once so I'd know.

But the waterproof liner should already be properly sloped to drain, so the foam piece is actually the second waterproof surface. I still think it simpler and more effective to use lath and mortar and get vertical sides and a sloped top.
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Unread 10-02-2021, 11:54 PM   #15
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I think I'd want both waterproof surfaces to be sloped toward the drain. I agree about wrapping the curb in lath and mudding it. If the overlay is rigid then it'll be hard to pitch the top without leaning the sides.
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