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Unread 08-06-2020, 06:38 PM   #1
mouseandcat
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waterproofing of shower/tub surround (amateur)

Hi all, wondering if I can get feed back on the bathrub/shower surround part of my bathroom remodel. I have read quite a bit of advice about waterproofing the area and thought I could ask for peoples' experience and guidance.

Background
- 'long' shower wall (https://i.imgur.com/If66TyV.jpg)
- home built in 1943
- 2x4 studs (nominal)
- i demolished all walls in bathroom down to studs
- i have no prior experience with construction/diy work but am learning (went so far as to buy plywood and cement board to practice tiling)

steps
- check that studs are 'in plane'
- check for squareness of the studs around the tub
- fill with insulation/something to dampen sound (the shower wall shares a wall with our bedroom)
- fill in 'layers' (going from outermost to innermost relative to the tub/shower)
adjacent room's drywall
2x4 stud
inslation of some sort (sound proof for adjacent room)
<---water proof layer--->
mortar
tile + grout

My research leads me to consider these options for my waterproof layer
(a) cement board (e.g. durock, hardiebacker) + roll on water proofing (e.g. redguard, truguard)
(b) drywall or cement board + kerdi membrane
(c) kerdi board + kerdi bands

I gather that kerdi products require some level of practice/experience. Hanging cementboard and slathering on redguard seems pretty straight forward. Cementboard + redguard seems to be much more forgiving for 'sloppiness'. I worry about using the right amount of mortar and all the mortar for the kerdi strips being level.

I'm leaning towards cementboard + kerdi membrane. Seems like a compromise for price and takes into account my experience (or lack thereof). Cementboard + redguard seems to be by far the cheapest option.

I have a couple of questions regarding my options:
(1) Is there a difference in longevity of water proofing among the 3 different methods?
(2) Is cement board + redguard just as waterproof as kerdi's products?
(3) Are there any products that allow for re-tiling in the event I need to cut out a section of the tiled area around shower/tub (such as if there was a leak or poor tiling)


edit1: clarify 'layers'
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Unread 08-06-2020, 09:13 PM   #2
jadnashua
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Properly installed tile will tend to damage the cbu if you try to remove one, regardless of what's underneath. You'll have a better chance of repairing the area with only roofing felt (tar paper) or plastic behind the cbu than one applied on top of it. If that were a shower pan, it would be more of an issue than on a wall.

Liquid applied stuff is prone to thin spots, runs, pinholes, any of which can compromise the end result. It must be installed in two coats, each in the proper wet film thickness. It's not hard to check, but you do need a wet film thickness gauge (they're cheap) and know how to use it properly. If your coat isn't within limits, you need to adjust your technique. In this case, thicker isn't better.

IMHO, once you understand installing a sheet membrane, it's not hard, but you do need to mix your thinset properly. Don't try to do large sheets, as spreading thinset is an art, and getting that done, then embedding the membrane in it when it's large isn't going to go well. Seams aren't an issue if your thinset isn't too thick, or you don't let it dry out on the wall before you try to embed it (wipe down the wall before spreading the thinset, and don't try to do too big of an area at once).
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Unread 08-07-2020, 10:07 AM   #3
mouseandcat
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> Properly installed tile will tend to damage the cbu if you try to remove one, regardless of what's underneath. You'll have a better chance of repairing the area with only roofing felt (tar paper) or plastic behind the cbu than one applied on top of it. If that were a shower pan, it would be more of an issue than on a wall.

got it, so i should not try to pick my layers to be able to make a significant repair. just a thought i had, if there was one backing better than the other for repairs, that would be one thing to sway my decision

> Liquid applied stuff is prone to thin spots, runs, pinholes, any of which can compromise the end result. It must be installed in two coats, each in the proper wet film thickness. It's not hard to check, but you do need a wet film thickness gauge (they're cheap) and know how to use it properly. If your coat isn't within limits, you need to adjust your technique. In this case, thicker isn't better.

why wouldn't thicker be at least as good as a proper wet flim thickness (2 or 3 applications)? My intuition tells me more layers be able to hide things like pinholes or thin spots?

> IMHO, once you understand installing a sheet membrane, it's not hard, but you do need to mix your thinset properly. Don't try to do large sheets, as spreading thinset is an art, and getting that done, then embedding the membrane in it when it's large isn't going to go well. Seams aren't an issue if your thinset isn't too thick, or you don't let it dry out on the wall before you try to embed it (wipe down the wall before spreading the thinset, and don't try to do too big of an area at once).

well i can't practice with kerdi membrane, that stuff is pricey. any suggestions on how i can practice installing sheet membrane? any cheaper alternatives to work with? maybe like a 3mil plastic sheet?
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Unread 08-07-2020, 06:14 PM   #4
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Liquid waterproofing materials need to properly dry prior to adding the second layer. When it's thicker than design (that's actually hard to obtain, you usually end up with it too thin!), it doesn't tend to dry properly. Plus, the stuff is slightly rubbery, and extra thickness isn't good for stability. People do successfully use the liquid stuff. Too thin, and it tends to not self-level.

The keys to properly installing Kerdi are properly mixing the thinset, dampening the wall so the thinset stays the proper consistency, and after you think you've got it, pull back a corner to check the coverage...it should have a uniform coating on both the membrane and the surface underneath, and if not, adjust your technique! Worst case, pull it off, scrape off the wall, and wash off the thinset from the membrane. It will come off if it hasn't started to cure (you've probably got at least an hour before that starts to any significant amount).
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Unread 08-08-2020, 12:06 AM   #5
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Mouse said, "Hanging cementboard and slathering on redguard seems pretty straight forward".

It really is pretty simple. Pinholes are not a problem when two even coats are used. It's more critical if you're making a shower pan out of it but for walls it's much easier and cheaper than Kerdi.

As far as repairs go, you'll damage Kerdi just as much or more than you will CBU.
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Unread 08-08-2020, 08:25 AM   #6
mouseandcat
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Quote:
Liquid waterproofing materials need to properly dry prior to adding the second layer. When it's thicker than design (that's actually hard to obtain, you usually end up with it too thin!), it doesn't tend to dry properly. Plus, the stuff is slightly rubbery, and extra thickness isn't good for stability. People do successfully use the liquid stuff. Too thin, and it tends to not self-level.
ok, every time i jump onto this forum i learn something new. i haven't priced out the kerdi membrane route for my shower/tub surround. once i do that i'll make a decision on the cement board or the membrane.

Quote:
The keys to properly installing Kerdi are properly mixing the thinset, dampening the wall so the thinset stays the proper consistency, and after you think you've got it, pull back a corner to check the coverage...it should have a uniform coating on both the membrane and the surface underneath, and if not, adjust your technique! Worst case, pull it off, scrape off the wall, and wash off the thinset from the membrane. It will come off if it hasn't started to cure (you've probably got at least an hour before that starts to any significant amount).
the thing that makes me lean towards the membrane is that i can use this opportunity to learn the product and method. but given that this is the first time i have ever done anything like this, another part of me says stick with the 'fundamentals' first. we plan on creating a full bath in the basement, so maybe i can practice with the membrane at that point?
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Unread 08-08-2020, 08:30 AM   #7
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Quote:
It really is pretty simple. Pinholes are not a problem when two even coats are used. It's more critical if you're making a shower pan out of it but for walls it's much easier and cheaper than Kerdi.
would three layers be too many layers, even if they are 'perfect' layers? perhaps too thick of a non-solid substrate for the mortar + tile?

Quote:
As far as repairs go, you'll damage Kerdi just as much or more than you will CBU.
assuming i go with cement board + 2 perfect layers of redguard, if a few tiles break (or fall off somehow) can i chip away at the mortar underneath and put in new tile? perhaps scrape off the redguard in that area as well and reapply another 2 layers of redguard? is that even possible? best practice for a small repair?
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Unread 08-08-2020, 08:53 AM   #8
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I've slapped 4 coats on before, I just make sure the coats aren't too thick and are dry before applying the next coat. The new formula membranes set much faster than they did just a few years ago.

For tub surround walls, either system will work fine and you can avoid the feared pinholes with the membrane. You'll find that hanging the Kerdi will be much more difficult than hanging CBU and applying the membrane. Again, it's much more critical on a shower floor than walls.

Repairs can be made over both materials. Even if you had to paint on new membrane or patch the Kerdi, it can be done. Again, it's not a shower floor. I've tore out tons of CBU tub surrounds that were 30 years old and didn't have any waterproofing at all. The last one was used twice a day for years. I advise some sort of moisture barrier but very few I tear out has one.

But, if you're wanting to practice with the Kerdi on this bathroom, this would be a good time to do it.
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Unread 08-08-2020, 04:05 PM   #9
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FWIW, if you decide to use Kerdi, forget the cbu, and just use drywall...cheaper to buy, bigger sheets so fewer seams, and it works. Some cbu panels (Hardiebacker is notorious for it) will suck a lot of moisture out of the thinset, making it stiff and really difficult to embed the membrane. If you use that with RedGard, you have to do a watered down coat to 'prime' the cbu, so it will accept the material properly when you do the next two...so, a watered down coat, then two 'normal' thickness coats. Don't really try three or more 'normal' coats. Talk to their tech support people.

Drywall is lots cheaper per sqft than cbu, and you can use regular screws. If you go with cbu and a liquid applied waterproofing, you have to tape the seams, fill with thinset, let it all cure, then paint on the two coats of waterproofing material. The smallest container of RedGard is over $160 for enough to do a typical shower. Throw in the cost of the cbu, screws, and tape, and Kerdi doesn't look bad at all.
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Unread 08-09-2020, 05:52 AM   #10
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I have to disagree with extreme prejudice.
I had to pull apart a 10' custom shower because the builder used sheetrock under membrane. It was completely saturated, rooted the framing, filled the wall with mold, and leaked constantly into the kitchen below. The moisture de laminated the membrane from the rock. It was a complete nightmare in a house less than 8 years old.

The difference in price between sheetrock and cement board is nothing, especially in relation to the cost of your remodel, and cement is available in multiple sizes by me.

I am a builder in nj, and have never had a callback with my bathrooms. Do whatever you choose, but my method is as follows.

In NJ, we don't use plastic in the walls, it used to be common in previous decades, and even required by inspectors in certain cases, but the result was mold in every wall. The theory being that the wall assembly needs to be able to dissipate moisture, and plastic just traps it.

Install 2x6 wood blocking/ stud on the flat as a nailer to install glass door later on.

I use pipe insulation on water lines, roxul batts in the wall. Roxul can handle moisture without losing performance, and in a shower you only need half a bag.

Set tub in bed of sand mix.

If you want over kill, you could use shower liner on floor.

Cement board with all seams properly taped and sealed with thinset, just like drywall, except using the proper tape.

Use pre formed shower niche. Located based on shower tile to be used, so tile lines line up with edge.

Silicone tub flange behind cement board.

Then install redquard according to instructions.

Thinset(not glue) based on tile size, back butter entire tile. Grout, then use appropriate color matching silicone in corners and edge between tile and tub.

Allow proper drying time for every step that needs it, do not rush. Having a fan in the room is helpful for piece of mind.

Treat the floor like a boat, no leaks. Seal everything, and try to locate toilet water supply on the wall instead of the floor.

Also, installing tile border instead of wood base trim can help water proof the edges of the room, but depends on your style and budget.

Haven't used kerdi, just confirm that if you install it, the warranty is valid. I know they were signing guys up to be certified installers.

Kerdi costs a lot more by me, the idea being that anyone could install it, so you save labor on a tile guy, especially if you're paying him to set mud pans in a shower since homeowners typically can't do that on their own. But for me, the price gap was so huge that it was never worth it. Not to say that it might not make sense for you, because it may. But 3 walls over a tub is super straight forward.

Good luck.

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Unread 08-09-2020, 07:46 AM   #11
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If you want to save time and make the work a little bit easier you could consider using the Kerdi board panels. It’s only a little more expensive than using the membrane and is much easier to work with. I am a diy guy doing my second project and the added cost was worth how much easier it made the job.
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Unread 08-09-2020, 08:59 AM   #12
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mykcuz, the reason the 8 year old shower failed wasn't because there was sheetrock behind the tiles. Sure, it made things worse when it leaked but it failed because the membrane (you didn't say which membrane) was installed incorrectly or maybe the wrong membrane was used. The shower would have still failed and rotted the framing if cement board would have been used.

Like you, I'm not a fan of sheetrock behind my tile walls but there are thousands of Kerdi showers out there that are holding up well. There are many acceptable systems and methods and they all fail when not installed correctly. The shower you mentioned was not done right, that's why it failed. The sheetrock made things worse but didn't cause the leak.
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Unread 08-09-2020, 09:08 AM   #13
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Respectfully, you did not inspect the shower, and cannot make absolute determinations about it. However, in my opinion sheetrock is not a product that belongs in moist/ shower environments, and for the negligible price difference there's just no reason to justify it.

Home depot online pricing.
4x8 green board- $15 or $0.47/sqft
3x5 durarock - $10 or $0.67 /sqft

We're talking about 4 boards in a 3'x6' shower tub, or $40 vs $60. It costs $20 to not have powdered gypsum and paper in a shower?

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Unread 08-09-2020, 02:25 PM   #14
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Quote:
Originally Posted by mykcuz
Respectfully, you did not inspect the shower, and cannot make absolute determinations about it. However, in my opinion sheetrock is not a product that belongs in moist/ shower environments, and for the negligible price difference there's just no reason to justify it.
Would you complain about drywall on your ceiling failing because the roof leaked? What about next to windows or doorways?

It's not all that hard to build a shower right, regardless of the method you use, but it does need to be done right, or you'll have problems.

If that shower had been built using cbu instead of drywall, the studs and everything would have been damaged as well.
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Unread 08-09-2020, 08:08 PM   #15
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Quote:
Originally Posted by mykcuz
However, in my opinion sheetrock is not a product that belongs in moist/ shower environments, and for the negligible price difference there's just no reason to justify it.
I agree with you and I always encourage people to install cement board behind Kerdi but, the fact is, that Schluter will warranty drywall behind their membrane so it's not wrong to install it that way.
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