Sealing framework behind vapor barrier? [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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09-06-2001, 06:17 PM
I'm working on a tub/shower rebuild and really want it to be bulletproof (this time). Have read about using either silicone caulk or cold roofing patch tar on the wood frame behind the vapor barrier. (Coming out from there, I plan to use roofing felt, ĹĒ HardieBacker, trowelable sealer, modified thinset, etc. Iíve read the posts, have Michael's book or order, and am working on Johnís book -- but, sorry, I doubt Iíll ever claim the title ďMud ManĒ.) I suppose if the seal on top of CBU holds, the seal on wood below is not required, but Iím willing to take the time just in case.
Any recommendations or comments?
-Mike Fossum (DIYer)

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Rob Z
09-06-2001, 06:49 PM
Hi Mike

You have a good start, reading MB's and JB's books.

If you are using a trowelable membrane on the surface of the hardibacker, then you can skip the stuff on the studs. If we assume the stuff works (and I've got a lot of jobs riding on that!), then no water is getting to...or through...the hardibacker.

Keep us posted on your project.

Rob Z

09-06-2001, 07:27 PM
Rob (& others)

I recently saw a waterproofing membrane on a newly constructed shower; It was applied over a wood framed shower seat. The guy that did the job did not smooth out the felt after applying the waterproofer ( asphalt cement over felt). The result was wrinkles and bubbles in the "paper". I have Michael Byrne's book as well and it doesn't comment on the final product being "smooth".

What's your advice on this? I wouldn't think the bubbled surface would be the best substrate. Also, how does the thinset adhere to the "felt" membrane?


Rob Z
09-06-2001, 07:52 PM
Hi Jason

If what you saw was roofing felt adhered to the wood substrate with asphalt gum...then that is not the same thing as a trowel applied membrane such as Laticrete 9235.

In MB book and the videos, he uses that method as a curing membrane or slip sheet below a mortar bed. The asphalt is to seal the punctures made by the fasteners holding down the felt and lath.

For a true waterproofing membrane, it's the latex in the thinset that bonds it to the rubberized surface of the waterproofing.

I had a chemist explain to me one time why latex allows stuff to bond that otherwise wouldn't bond. I don't remember the reason, and now just say "It Does It".


09-06-2001, 09:47 PM
So what about the bubbles and wrinkles in the paper?

Does this make the substrate inferior? It seems like the tile would be bonded to a portion of loose paper. If the section of the loose paper is sufficient in size ( relative to the tile size) I don't see how the job would last


Rob Z
09-06-2001, 11:04 PM
The bubbles and wrinkles are a no-go. Definate problems.

09-07-2001, 08:26 PM
Hi Rob,

I have a similar post under another topic but I believe it is relevant here as well.

You say you have a lot of jobs riding on the troweled sealer ( laticrete 9235) and therefore sealing the studs/frameowrk should be an issue. If that's the case, the felt shouldn't be needed either..Right?

Help me out here...I know the 9235 is probably high dollar but worth every penny if it is truly "waterproof"

Do you use the 9235 on the floors as well? seems to make sense


Rob Z
09-07-2001, 09:06 PM
Jason and Mike

Yes, the 9235 is supposed to be completely waterproof. You can use it to build fountains, tubs, and other water-holding vessels. It definately eliminates the need for any vapor barrier behind the cement board or mortar.

I have used it on shower floors, under the tile, in addition to the pan liner under the mud.

Cost: I buy in bulk, and get a good discount. The material cost to waterproof a standard tub surround is probably $60, which includes throwaway paint roller, disposable gloves, etc.

I don't use it on mud floors because of the drying time and not being able to walk on it for the second coat.

For waterproofing a mud floor in a bathroom , I use Schluter ditra with kerdi at the seams and coves. I'm doing one tomorrow in a bathroom that is really getting all the bells and whistles. 30+ grand in a 5 x 9.5 bath, getting photographed for some fru-fru magazine that the designer caters to.


09-07-2001, 09:33 PM

Better dress up nice for the photographers. How about posting a picture when it's done. Didn't know you could get 30K in a 5X9 bath.

By the way, Custom's version of the waterproofer / anti-fracture membrane goes for $50 a gallon ; what about the Laticrete?


Rob Z
09-07-2001, 09:37 PM

They won't taking pics of my ugly mug.

The laticrete plus fabric is about the same, when bought in bulk.

John Bridge
09-08-2001, 11:40 AM

If you're around when the photogs arrive you can ask them for copies of the out-takes. Otherwise, get out your brownie and make sure we get a look at that.


I can easily pack more than thirty grand into a small bath. Hell, some of the faucets and fixtures cost that much. I once was working on a double bath vanity that had the faucets mounted on the deck. I asked for the fixtures so that I could make sure I had the through-deck holes right. The builder just laughed and said I'd have to go by the spec sheet. Seems the faucets had portions that were pure gold.

Sorry I got off track again, Rob. Maybe you'll have to ban me from the shallow end.