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Unread 03-05-2007, 12:05 PM   #1
airplaneguy
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Tub surround niche questions (water proofing)

I am still in the planning phase of my tub surround rebuild. I know what I want to do and how to do it from reading all the different threads on this subject, but I am getting a little confused. I have been at this point for a couple of weeks and, quite honestly, I am scared to start! I would rather not use Kerdi on this shower, since it won't get much use over the next 6 or so years and I am already down to the studs.

I am going to install a vapor barrier behind the 1/2" CBU then tile with 6" white ceramic tiles. I really like the look of built-in niches and I would like to put in a shampoo shelf over an area for soap on the "long wall". I read in John's book how to build the niche and I very comfortable with that. I understand that I will need to Redgard the niche for water proofing, but:

Q1. How do I work in the vapor barrier behind the niche? (Do I just cut a hole in it?)

Q2. Since I am going to Redgard one area, do I have to Redgard the entire surround?

Q3. Is there something else I can use instead of redgard?

Thanks in advance for all the help!

Ben
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Unread 03-05-2007, 01:08 PM   #2
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Ben,

My 2 pesos:

Q1. You're building a frame for your niche before installing CBU, right? You can seat a separate piece of poly in there just like the rest of the wall (separate piece behind the wall poly on the top, in front of the poly on the bottom - think how you would lay shingles) however I doubt poly is necessary in a niche coated with Redguard. Reason is that the niche is probably high enough that no moisture is coming down the CBU from above, and the Redguard keeps the moisture from getting in around the niche, but that's my speculation. I'm thinking that if you have to buy a tub of Redguard anyway, why not skip the poly and coat the whole surround?

Q2 No if you poly the surround

Q3 Other than Kerdi, which you're not interested in, there's another similar product discussed here that I don't know the name of. Cost/performance/availability-wise I don't think the two coated products are any different (Redguard is at Homer's)

Since you're an airplaneguy and I'm a bikeguy, let's not race.
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Unread 03-05-2007, 02:16 PM   #3
airplaneguy
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Thanks for the quick reply, bikemike. I used to be somewhat a bike guy myself. I just work with airplanes, they won't let me drive them!

I see what you are saying about shingleing the poly. Makes sense. I am just really scared of water getting behind the CBU. I would Redgard the whole surround, but it seem pretty pricey since I got 80 sqft or so to do.

The lower niche will probably be 4"-6" above the tub so I think it will see quite a bit of water.

Thanks again!
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Unread 03-05-2007, 02:32 PM   #4
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You might cover 80ft2 with 2 gallons of redguard if you're careful - cutting it close at the correct thickness for waterproofing.

The expensive part of the project is your time, so what's another gallon of redguard? Or for about $70 you could buy a preformed waterproof niche.

Any spare redguard sitting around the airplane hangar?
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Unread 03-06-2007, 08:07 AM   #5
airplaneguy
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No redgard sitting around the hanger that I can find!

I ran across this post from tileguytodd from a few years back (2/4/04) and I think this makes sense:

"All kidding aside,the amount of moisture potential is so minimal as to be virtual moisture,non existant,ghost water etc.for that small area you and i wont worry about it in our lifetime or our kids lifetimes
you do need to seal and maintain your caulk though,OK "

I am just going to redgard the niche area and save the rest for the M.B, shower which comes next, whenever I get this project done.

Thanks for the help!

Ben
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Unread 03-06-2007, 08:25 AM   #6
Shaughnn
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Hello Ben,
Rather than building your niche from scratch, try looking at one of the pre-formed niches from Noble Products . These are blocked into place, taped and thinsetted to your Wonderboard and then the whole thing can be sealed with Redgard. The niche itself is completely waterproof, but the joint between the niche and the CBU is vulnerable.
IF using Redgard, or any of the other topical waterproofing membranes, you don't need a vapor barrier BEHIND the CBU also. Using both can trap moisture, which you don't want.
Best of luck,
Shaughnn
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Unread 03-06-2007, 09:37 AM   #7
airplaneguy
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Smile

Thanks for the quick reply shaughnn!

I have looked into the preformed niche, but I think I am going to try building one first. Should be good experience and that is what I do most of my projects for!

What I don't understand about the Vapor barrier is how much water are we talking about getting behind the CBU? Is the vapor barrier just to keep the studs dry or are we talking about a lot of water flowing down the poly back to the tub lip? If it is the later, how do we deal with the hole in the poly for the niches?

Thanks again and I promise one day to stop asking these questions!
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Unread 03-06-2007, 12:36 PM   #8
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Ben,

Your niche is low - it will likely get wet and you need it to be waterproof. Unless you are comfortable that you can build it that way yourself I would buy the preformed niche.

When the shower is in use, water enters the CBU slowly through grout lines and wicking up from the bottom and rapidly through any unintended voids such as a non-waterproof niche. If the shower is used routinely the CBU will remain moist. At a minimum mold will appear in grout and caulk lines. Worse situations include rotting lumber, subfloor, nearby drywall etc which we could debate the likelihood of this occuring in a tub surround.

Let's just skip the debate and build this thing the right way, OK? Many people here are in a worse situation, trying to work with something already half-built to non-ideal conditions. There are a lot of smart people here to help you out, and Shaughnn's an ace (just look at him with that knife and eyepatch - you going to argue with that?)

Oh, and don't underestimate the value of a good vent fan in a shower area. Good luck!
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Unread 03-06-2007, 02:05 PM   #9
airplaneguy
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bikemike-

Re-reading what I wrote I see the confusion. I will be Redgarding the niche and the surrounding areas (approx 2") and I will be using a vapor barrier behind the rest of the CBU. I wouldn't think of doing it another way!

I was looking for clarification about how much water normally gets behind tile and into the CBU? I know I am missing something. If water is getting into and behind the CBU, does a vapor barrier just protect the wood?

I know I am probably sounding incredibly dense right about now.

Ben
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Unread 03-06-2007, 02:25 PM   #10
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Ben,

The vapor barrier protects everything behind it from moisture migrating from the CBU. Water beads up on it and travels down, which is why you want the poly over the tub lip and not behind it.

Again, the amount of water depends on how much you use the shower. Think of CBU as a sponge because it will suck up and hold a lot of moisture. This moisture can promote mold/mildew growth in a shower. In another post Rob Z mentioned he demoed a shower where the CBU was wet about 3-4 feet up the wall. Vapor barrier = good.

I don't know what more can be said.
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