Why does drywall work in a Kerdi Shower?

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Jadnashua

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Trying to install large pieces of Kerdi should be left to experienced people...it is just too hard for the average DIY'er to key in, notch and then cover large areas with a single sheet of Kerdi before the thinset skins over. The videos on the Schluter website talk about this. Not pulling the membrane back to verify proper coverage is the main reason why a seam will leak - the thinset is either too dry initially, or it skinned over before it is covered and this prevents proper bonding. The same thing will happen with tile if you spread too much thinset out...the tile's won't bond well.
 

Patriotrider

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New member, old thread. Starting second shower with Kerdi kit. Having done a 500 sqft room addition with a roof/balcony over living area , (code inspected OK), using Advantech, Durock cement board and Ditra (waffle) membrane, covered with tile, ...its good stuff, pricey but no worries about leaks. Although drywall shower walls with Kerdi gives me a high confidence level, either way should be fine IMO. Cost nor level of effort is a concern as I’m confortable with installation hassels, but long term stability is the goal. Always spend the time and money to do it right, even if its overkill for my long term retirement home.
But for a hot shower, I am wondering if cement board expansion with hot/cold is a concern for large tiles?? Recall the Ditra was an uncoupling membrane, don’t think Kerdi is. Thanks for replies.
 
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Jadnashua

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If you look at it this way, once you have the area grouted, it tends to act as a single, large tile, regardless of whether it is lots of small ones, or one large one! The key is to follow industry standards, and allow for expansion and/or movement at all changes of plane. If you don't like to use caulk, Schluter (and some others) make engineered expansion joints specifically for this. In fact, Schluter's first products were profiles...Kerdi and Ditra came much later in the company's history. Of those that make them, IMHO, Schluter has the largest selection, but that doesn't mean others may not have one that suits you needs or desires.
 

OnlyinCali

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Love this conversation... This brings up a new question.....

Is there anything wrong with going total overkill and doing the following

1. Roofing felt on studs
2. Cement Board
3. Kerdi product or Red waterproofing paint.

This way IF water gets past its still not hurting anything.... It also allows you to use the red waterproofing paint (cheaper and easier) while still maintaining a true "backup plan". Other than a few bucks of extra cost, why WOULDN'T this be used on a home project where 100 bucks of peace of mind far outweighs future risks?
 

Jadnashua

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While both properly installed Kerdi and RedGard are waterproof, neither one is vapor proof. Adding a second moisture barrier in the stackup could trap some of that vapor, depending on temperatures, use factor, and the humidity levels.

In either case, it's best to follow the manufacturer's instructions and not try to second guess their engineers and years of field experience. Should you decide to use RedGard, do buy yourself a wet film thickness gauge and learn how to use it properly...the stuff does need to be applied between the min/max, and extra coats or thickness is not necessarily a good thing.

FWIW, most showers are built with water resistant walls, not a totally waterproof enclosure. They've worked for centuries. Having waterproofing directly beneath the tiles has some advantages. Neither tile nor grout is waterproof...some moisture will get beneath them. The less materials there that can absorb it, the quicker it can dry out. In a well-used traditional mudbed shower pan, the entire pan's upper layer (nominally at least 1" thick, probably more) is damp after a few months of use.
 

Atomic1

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Exactly, sandwiching layers of membrane is never good.


For those you DIY'ers afraid of dealing with installing large areas of kerdi membrane, I'd suggest looking into kerdi board. Is a few bucks more, but is definitely a lot easier to install and mates up to drywall very nicely.
 

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Gmc742

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We are redoing our main shower and I just gutted it. It was original. Just cheap tiles over drywall. There was absolutely no mold. I couldn't believe it. The tiles had cracks and a soap dish built into the wall had rusted and split. 4 people used it. It was 30 years old. I will be putting kerdi over drywall on the new one
 
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