Green/Cement Board Overlapping Tub Flange vs Leaving Gap Between Board and Flange

[johnfrwhipple]

I'm confused but not frustrated. You have a lot of good information here and I just need to sort it out. For example the picture of the tub with Noble TS and Aqua Defense surprised me. I would have thought the Noble TS (installed per Noble's spec's) is a waterproofing membrane by itself. I wouldn't have thought to add the Aqua Defense on top of it. Also the Aqua Defense I'm aware of is made by Mapei. I'm not questioning your work, but I don't have the knowledge to do that.

What I'm looking to do is build a tub/shower surround that will give me years of worry free use. As for the backer board choice, I don't really care. I'm doing this for my home and the difference in cost of Durock vs DensShield vs Hardiebacker vs drywall will not have a big impact on the budget. Also, the time required to cut and fit the backer board is also not important. Being the homeowner gives me those options. What is important is that it not leak for the next twenty years (at least).

Originally I planned to use 15# roofing felt and cement backer board. But replacing the felt behind the backer board with a waterproofing membrane on the front seems like a better approach in theory. I have to depend on you to tell me if in practice it really is better. And if it is better, then what are good systems to use? There are those who prefer the Kerdi membrane. (I wasn't considering Kerdiboard.) Is Kerdi head and shoulders above the rest? If so, I'll use it. But are there others that are just as good? As you say, you do things above industry standards and that's what I'm wanting as well.

Also, after the tub/shower surround, the next project is a walk-in shower. I would like to use the same waterproofing system on it.

Kerdi Board in a word - "Sucks". If you want to stay with a single system then you should be looking at Kerdi over cement board with Kerdi Fix.

This approach will give you the piece of mind on using one system only but will net you the smallest warranty in the industry to my knowledge. 5 Years.

Remember the key step in my system is the sealing of the bottom flange to the backer boards waterproofing.

You might look into Wedi's system. I have yet to try them but they make a backer board similar to Kerdi Board and also have a sealant similar to Kerdi Fix. I'm not sure if the Wedi Board bows or flexes as much as Kerdi Board.

The biggest single problem with Kerdi Board is doing a repair later if need be or durning the installation. You can't bang the tiles off the wall with a hammer without risk of damaging the board below the tile not in question.....

If you want Kerdi Board - make it yourself with cement board and then Kerdi.

Now if you want to double the five year warranty when using Kerdi to a ten hyear warranty AND use modified thinsets* (much much better) then use Ardex Setting Materials X5 or X77 I believe with KErdi. Ardex makes a product called 8+9 which we recently embraced and are using on three projects as we speak. Ardex makes a product called SK Mesh which is similar to Kerdi Band. I would imagine it could be set to the tub's flange with 8+9


* Call Ardex to get the product details on the ten year Kerdi Warranty. You need to use the right products and grout from Ardex as well.

[CF]

Now I'm adding to the confusion. I am NOT interested in using Kerdiboard or Wedi at this time.

Is there a way to compare the durability of the waterproofing systems from Kerdi, Nobel, Laticrete, Mapei and Ardex? For example, how do the sheet waterproofing membranes from Kerdi and Noble compare to the liquid applied systems from Laticrete, Mapei and Ardex?

As you say, the hardest part is the connection of the tub to the backer board. The Kerdi installation instructions show Kerdi-Band bridging the backer board to the tub. Thin set was troweled on to the backerboard and a bead of Kerdi-Fix on the tub flange. Then the Kerdi-Band was pressed into both of them. Your first picture in post #3 looks exactly like that. Your picture in post #5 shows another example with Hydro Ban liquid coating on the backer board and Kerdi-Fix at the tub flange. In this case did you fill the gap between the backer board and tub using Kerdi-Fix only? There doesn't appear to be a sheet membrane between the tub and backer board. I'm assuming the Kerdi-Fix is the dark grey material in the picture.

Thanks for your help. This is very informative.

[johnfrwhipple]

Now I'm adding to the confusion. I am NOT interested in using Kerdiboard or Wedi at this time.

Is there a way to compare the durability of the waterproofing systems from Kerdi, Nobel, Laticrete, Mapei and Ardex? For example, how do the sheet waterproofing membranes from Kerdi and Noble compare to the liquid applied systems from Laticrete, Mapei and Ardex?

As you say, the hardest part is the connection of the tub to the backer board. The Kerdi installation instructions show Kerdi-Band bridging the backer board to the tub. Thin set was troweled on to the backerboard and a bead of Kerdi-Fix on the tub flange. Then the Kerdi-Band was pressed into both of them. Your first picture in post #3 looks exactly like that. Your picture in post #5 shows another example with Hydro Ban liquid coating on the backer board and Kerdi-Fix at the tub flange. In this case did you fill the gap between the backer board and tub using Kerdi-Fix only? There doesn't appear to be a sheet membrane between the tub and backer board. I'm assuming the Kerdi-Fix is the dark grey material in the picture.

Thanks for your help. This is very informative.

Is there a way to compare the durability of the waterproofing systems from Kerdi, Nobel, Laticrete, Mapei and Ardex? For example, how do the sheet waterproofing membranes from Kerdi and Noble compare to the liquid applied systems from Laticrete, Mapei and Ardex?

Sheet Membranes are better but harder to apply. They offer up more strength in the inside corners and change of planes. Between Noble and Kerdi - Noble wins every time in my book. Thicker. Better.

As you say, the hardest part is the connection of the tub to the backer board.

So true. This is not only hard there is no detail offered up by the TTMAC or the TCNA that I like.

The Kerdi installation instructions show Kerdi-Band bridging the backer board to the tub. Thin set was troweled on to the backerboard and a bead of Kerdi-Fix on the tub flange. Then the Kerdi-Band was pressed into both of them. Your first picture in post #3 looks exactly like that.

That is what I did. I also ensure that the Kerdi fix filled the slight gap between the Kerdi Board and the shower pan.

Your picture in post #5 shows another example with Hydro Ban liquid coating on the backer board and Kerdi-Fix at the tub flange. In this case did you fill the gap between the backer board and tub using Kerdi-Fix only?

When I arrived to this job the boarding was done for me. I used Hydro Ban to coat the underside of the backer board after I blew the dust away. I used three coats to get up under the backer board and used a small trowel to help. Once dry I then filled the space with Kerdi Fix (Grey). This approach is not approved by Laticrete or Schluter. It would be easier to just skip this step and call it a day. That is juts not my style.
There doesn't appear to be a sheet membrane between the tub and backer board. I'm assuming the Kerdi-Fix is the dark grey material in the picture.

Thanks for your help. This is very informative.

Hopefully you are getting less confused!

[CF]

Thanks again for your help. The confusion is much improved. For the sheet membranes, Noble appears to be the easiest for the DIYer to buy. The have an online store at noblecompany.com. Home Depot can get Schluter-Kerdi but I don't think they stock it.

Is there a durability advantage to using cement backer board vs. fiber cement (Hardie) or gypsum backer board (DensShield or drywall)? The cost difference is not that significant. If somehow the membrane failed would the cement backerboard help or hurt or make no difference?

For the Noble sheet membranes, do you prefer the Noble TS or the Noble Wall Seal for wall applications? The Wall Seal is 0.025" thick and Kerdi is 0.008".

Is there still a debate as to whether Kerdi should be installed with modified thin-set vs non-modified thinset? Their instructions still call for non-modified thinset.

Is there a problem with the membrane seams telegraphing through to the tile? Does that affect whether you install the sheet membrane vertically or horizontally (shingle style)?

[johnfrwhipple]

Thanks again for your help. The confusion is much improved. For the sheet membranes, Noble appears to be the easiest for the DIYer to buy. The have an online store at noblecompany.com. Home Depot can get Schluter-Kerdi but I don't think they stock it.

Is there a durability advantage to using cement backer board vs. fiber cement (Hardie) or gypsum backer board (DensShield or drywall)? The cost difference is not that significant. If somehow the membrane failed would the cement backerboard help or hurt or make no difference?

For the Noble sheet membranes, do you prefer the Noble TS or the Noble Wall Seal for wall applications? The Wall Seal is 0.025" thick which is about the same as Kerdi (I think).

Is there still a debate as to whether Kerdi should be installed with modified thin-set vs non-modified thinset? Their instructions still call for non-modified thinset.

Is there a problem with the membrane seams telegraphing through to the tile? Does that affect whether you install the sheet membrane vertically or horizontally (shingle style)?

I just installed my first little bit of Noble Wall Seal a few weeks back. It is way thinner than Noble Seal TS and still thicker than Kerdi. You can install it if this shower is not a steamer with Noble Company's Noble Bond XT I think it's called. Or you can install it with any kind of thin set.

How long do you have to do the waterproofing and tile job? If you in a rush then working with a rapid setting thin-set would be the smartest.

Noble Seals it's sheets together with Noble Sealant 150 NOT Thin-set. As for lapping and overlapping it does not matter.

Most wall tile is 3/8" thick. Most times thin-set thickness is 1/4" (max allowed by thin sets). This gives you a 1/4" wiggle room behind the tile. One, two or even three plys will not project further off the wall than that.

Working with a sheet membrane is much harder than a liquid or cementious membrane like Ardex 8+9 or Laticrete's Hydro Ban. Get a helper and install smaller sections.

I do not like the composite backer boarders so much. We use Hardi on occasion but prefer plain cement board or the eco friendly backer board called Green EBoard. Lately I have noticed that the Green EBoard is not being made like it used to - before you could install it rough side out but now it appears to be only the smooth side that should be installed out.

Once you board your job you should give it a good clean, vacumm and then a skim or scratch coat of a good thin set. Backer boards suck the moisture out of thinset quickly - this pre-step extends the working time you get (especially if you use a modified thin-set as both your scratch coat and setting material for the sheet membrane)

If you want some more tips on installing Noble email one of these two techs.

Eric Edelmayer <eric@noblecompany.com>

Richard Maurer <richard@noblecompany.com>

Eric and Richard are very helpful guys and most times one of the two is at head office.

JW

[Freddie]

Hi John,

Not so keen on using drywall or Denshield (which has a layer of drywall) in the shower even with topical coverage...just in case. Cement board seems the obvious and proven alternative with hydroban on top. I will have a vapour barrier behind the cement board. Should water get into the cement board it's not getting into the wall. Now the question is where will that water go if the bottom of the backerboard is sealed at the base / at the junction to the shower acrylic base? Looks like it will run down the backer board and collect at the bottom with no place to drain to.

Would it make sense to just not seal the bottom of the backerboard with hydroban , nor silicone the gap between the tile and the shower pan so that water candrain into the shower pan?

[jadnashua]

Don't use a topical waterproofer with a vapor barrier behind the sheet goods...one or the other, not both.

[johnfrwhipple]

Hi John,

Not so keen on using drywall or Denshield (which has a layer of drywall) in the shower even with topical coverage...just in case. Cement board seems the obvious and proven alternative with hydroban on top. I will have a vapour barrier behind the cement board. Should water get into the cement board it's not getting into the wall. Now the question is where will that water go if the bottom of the backerboard is sealed at the base / at the junction to the shower acrylic base? Looks like it will run down the backer board and collect at the bottom with no place to drain to.

Would it make sense to just not seal the bottom of the backerboard with hydroban , nor silicone the gap between the tile and the shower pan so that water candrain into the shower pan?

Hi Freddie.

We like to take our concrete board or GreenEBoard (not for steamers) out a little past where they need to be and then skim and tape them like drywall. What little water that can migrate either side can wick and evaporate on these edges. We also like to only waterproof to the height of the shower head or 6' off of grade roughly. This leaves more room for evaporation and wicking up.

The connection point from the tub to the backer board is key. Kerdi Fix and Kerdi Band work great. You might pre- coat your cement board with the fleece to get a nice application of Hydro Ban on the bottom and then Kerdi FIx that.

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