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Unread 03-19-2021, 02:09 PM   #1
wisegirl99
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Proper way to waterproof shower

We are remodeling our shower, and have questions about waterproofing:

1. I have seen videos where people are putting the paintable waterproof membrane over their entire finished cement pan, even though there is a PVC liner under the pan. I was planning on doing this as well until I read online that this would create a "mold sandwich". Would it be fine to paint the membrane on the walls and down to the pan, covering the pan about 10 inches or so around the outside perimeter? That way if water seeps down into the cement that doesn't have the membrane, it can make its way to the weep holes. What do you recommend?

2. In setting the cement board on the walls, I have seen several videos where they say not to let the bottom of the cement board touch the pan, and to leave a 1" gap from the bottom of the cement board. Then to tile the floor, pushing the tile underneath the gap. After grouting, there will be about a 1/2" gap left at the bottom. Do you advise doing this? In the Starrtile videos on youtube, he says to use a paintbrush and apply the waterproof membrane inside of the gap first, then to install your wall tile down to your floor tile. There will still be a gap behind the bottom of the wall tile. Should I apply caulk to this gap before tiling? Or should fabric be applied first, then the liquid waterproof membrane?*Thanks!



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Unread 03-19-2021, 03:40 PM   #2
Lazarus
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The only thing I could add is that StarTile violates just about everything about building showers.

Try anything with Sal DiBlasio on YouTube. Unlike the former...he actually knows what he is doing.
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Last edited by cx; 03-19-2021 at 06:47 PM.
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Unread 03-19-2021, 06:40 PM   #3
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Welcome to the forum. You will learn everything you need here.

This is where I would start:

https://www.johnbridge.com/vbulletin...ead.php?t=5434

Lots of info in the Liberry (Link above)
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Unread 03-19-2021, 08:39 PM   #4
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Quote:
Laz; The only thing I could add is that StarTile violates just about everything about building showers.

Try anything with Sal DiBlasio on YouTube. Unlike the former...he actually knows what he is doing.
I agree with Laz. Sal puts out some very informative content.

I might add Isaac Ostrom on YouTube “Tile Coach” is fantastic as well.
He is a licensed Tile installer in Cali.

Then again the guys here at JB are awesome too.
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Unread 03-19-2021, 11:22 PM   #5
jadnashua
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The only part of a shower that is required to be actually waterproof is the pan. The walls do not have to be, and haven’t been for centuries and some of them are still working fine.

I much prefer a different technique if I wanted an actual waterproof shower, and I’d use a sheet membrane rather than a liquid applied one as then, you only need to worry about the joints versus the thickness, runs, pinholes, voids of a painted on one. Noble and Schluter have been around the longest with products designed for this. Schluter has lots of videos you can binge watch to see how their system works.

If you choose to use a liquid applied waterproofing, carefully read THEIR installation procedure for building a shower. There are numerous methods of building a reliable shower outlined in the TCNA handbook (the industry bible) that is augmented by the manufacturers’ instructions and ANSI specs to fill in, along with the plumbing code.

There are two classes of CBU boards...one classified as a fiber cement board CANNOT be embedded in the pan, and must be terminated above the top of the pan...the other type of CBU can be embedded in the pan without issues, and is the easier one to use as you can pack the mud bed over the bottom edge to hold it in place without penetrating the pan liner. A surface applied sheet membrane may allow you to actually use drywall on the walls of the shower for those with the proper certifications, as they recognize the drywall is protected well enough that it should never get wet. None of the liquid applied membranes have passed that test.
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Unread 03-21-2021, 10:06 AM   #6
wisegirl99
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Cement board touching the mud pan or not?

I've read in some places to not set your cement board into the mudpan because it can cause wicking. But now I am reading in most places that if you have a PVC panliner, you should set the board into the pan when making the final mud bed. We have already finished our final mud pan But have not yet installed the cement board on the walls. We have Wonderboard Lite Cement Board. Should we install the cement board all the way down to the mud pan? Or should we keep a gap. And if we leave a gap, how do we waterproof that gap?
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Unread 03-21-2021, 10:19 AM   #7
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Hi Laurie, we've merged your two threads so that everyone can see what questions have been asked and answered for your project. We can rename the thread if you'd like.

Since you are using a true cement board you could have installed it directly into the top mud bed, which is beneficial because the top mud bed will hold the bottom of the cement board against the studs since you are not supposed to screw the cement board into the studs any lower than 3 or so inches above the top of the curb. For instance, if you curb is 2" tall as measured from the shower floor, the lowest screws for the cement board would be 5" from the shower floor.

But that ship has sailed.

Install the cement board down to within 1/8" to 1/4" of the mud bed. Because this is a mud/liner/mud shower receptor you do not need to water proof the cement board to top mud bed joint. Any water draining down the wall behind the tile will flow into the top mud bed, down to the liner, and - if pitched correctly, across the liner towards the drain.
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Unread 03-21-2021, 02:46 PM   #8
jadnashua
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As I said earlier, there are two classes of cbu boards, and the shower build methods are different, which can add to the confusion. Run the one you have down, then build your mud Ed up against it. If you have followed industry guidelines, you'll either have a moisture barrier behind it, or surface waterproofing on top of it. If wicking is a big concern, a sheet membrane method would have been a better choice. Done per industry standards, it's not a problem.
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Unread 03-21-2021, 06:23 PM   #9
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Thanks for all of the advice on here. I have a another question.. I am using quikrete stucco base coat to build my curb. After I set my cement boards, can I use this same stuff to fill in the small gaps between the cement board and the pan? (Jadnashua mentions to fill mud in the gaps) Also I noticed some areas in My Pan where the pitch isn't perfect. Can I also use the quikrete stucco to fix the pitch in my pan? Or should I use the quikrete sand topping mix that I used to make my pan to fix these corrections?

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Unread 04-02-2021, 06:53 AM   #10
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Should I use waterproof fabric when I already used fiberglass mesh tape?

We are about to apply the liquid waterproofing membrane aquadefense to our shower for waterproofing. I have already used the fiberglass mesh tape in the corners. I am wondering if I need to also use the fiberglass fabric for the liquid waterproofing on top of the mesh tape in the corners. Thanks!

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Unread 04-02-2021, 07:16 AM   #11
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Laurie, I don't think the mesh tape used for reinforcing the CBU panels is the same as that used for the AD. But, if you installed the CBU mesh tape with thinset mortar then you don't need the extra tape. Just be certain the AD completely covers the mesh taped and mortared joints.

Also, we've merged your two threads since they pertain to the same project. Having all the previously asked Q's and A's in one place helps all contributors have the big picture. We can rename your thread if you like, just let us know.
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Unread 04-02-2021, 07:42 AM   #12
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Laurie, you want to read and follow very carefully the installation instructions for that Aquadefense material. If you've not used such a product before, don't be misled into thinking it's like painting the bedroom walls. It is not.

The final minimum thickness of the dried material is 20 thousandths of an inch. That is a very thick profile for a liquid-applied product.

MAPEI says the reinforcing fabric is optional, but I'll suggest you'll have a very difficult time achieving the 20mil thickness without it.

My opinion; worth price charged.
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Unread 04-02-2021, 02:11 PM   #13
jadnashua
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My biggest gripe with painted on waterproofing material is that it's harder than you think to get a solid coat between the min/max thickness without runs or pinholes. Give ten people a roller and tell them to apply, and you'll get ten different end results because of how many times they go over a spot, how hard they press, and how much material they start out with on the roller.

Go to a paint store, or buy one online, and pickup a wet film thickness gauge as you can't really measure the end thickness after the stuff cures...you need to measure it while it is wet, thus, why they call it a wet film thickness gauge. They're cheap. They do make electronic ones that aren't, but you don't have to interpret them like you do with the cheap ones. The coating shrinks as it cures, so you need to verify the WET film thickness required. And, more is not better! Two coats, properly applied is how it was tested and certified.

https://youtu.be/bwIhWu25O2s
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Unread 04-06-2021, 09:53 AM   #14
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CX makes a great point; getting that mil thickness correct is crucial. While the reinforcing fabric is optional, (and again to CX's point) it serves very well to help ensure the mil thickness is where it needs to be, along with reinforcing the waterproofing membrane.

A wet film gauge as Jim suggested would be a great thing to have on hand when applying, to check as you go. Once dried, Aquadefense will be approximately the thickness of a credit card.

Another good tip is to roll the waterproofing membrane on in different directions for each coat. For example, if you roll the first coat North and South, roll the next one East to West (or vice versa).
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Unread 04-10-2021, 08:02 PM   #15
wisegirl99
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Back butter tile with flat size or notched side for LFT?

I am tiling a shower wall with 3/8" thick 12x24 porcelain tile. I have a 1/2" x 1/2" trowel. I know that I obviously need to use the notched trowel on the walls, but when I back butter the tile, do I use the notched side as well, or the flat side?

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