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Ditra & Kerdi Band

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11K views 16 replies 6 participants last post by  PootyTang  
P
#1 ·
I know that Schluter recommends Kerdi Band for sealing the seams on Ditra for waterproofing. I have never used Kerdi Band for this but had a question. If the Kerdi band is bonded to the Ditra with thinset, then won't water just go under the Kerdi Band through the thinset it was bonded with? I mean there is a smaller layer of thinset between the Ditra and the Kerdi Band but thinset nonetheless. I don't see how it could stop water any better than the thinset under the tiles could.
 
T
#2 ·
I just over lap the fabric by 2” in most cases.

Surface area and the dimples in the fleece——the thin set pressed between the 2 membranes has an exceedingly small exposed edge, if you look at the fleece you’ll see that the fleece is dimpled, the mortar mechanically bonds the pieces together, the edges of the dimples act as small dams.

Tom
 
P
#4 ·
Hi Tom, you said mortar will not stick to Ditra, that's where I don't see how the thin layer of thinset between the Ditra and the Kerdi Band could possibly stop water. If it did stick, or another adhesive was under the Kerdi Band I would understand, but I just don't see it. Probably a case of it works good enough, and if there was enough of a flood it probably wouldn't matter anyway. But I just think it gives a lot of folks a false sense of security.
 
T
#5 ·
If you look at Schulters logo it is a series of dovetails. The bond to Ditra is mechanical.

I’ve done wet rooms with Kerdi band on seams and Kerdi lapped 2.5” from wall to floor. Flooded the room, no water loss/leak for up to as long as 48 hours. These rooms have wall mount toilets with no floor penetrations.

Tom
 
P
#6 ·
I'm not sure we're talking about the same thing. I am talking two sheets of Ditra butted next to each other on the floor - then over that seam a strip of Kerdi Band is bedded in thinset. Now if the bathroom floods, the water will wick through the grout, through the tile thinset, and finally try to get under the Kerdi Band. The only thing keeping it from getting under the Kerdi and into the Ditra seam is thinset !!! And the whole point of seaming is because the thinset below the tiles is not waterproof. So we are using thinset (non waterproof) to secure a waterproof seam tape, just doesn't make sense.
 
T
#11 ·
My third post does refer to Ditra on a floor with 5” band over the floor seams and sealing the wall to the floor. Doorways are sealed for the test with Kerdi board. I also flood test zero entry showers the same way.

Strata Mat has vents in it, avoid using it if you need a waterproof floor.

Tom
 
F
#7 ·
I've done a few dozen Kerdi showers. You should tell them that you found the flaw in their system. Class Action them. Or just accept that if you follow their requirements, you'll be covered by some type of warranty. 50 posts and you haven't figured this stuff out?.
Educate yourself about the project you are doing. I think that is the rule. Don't ask questions here that are best asked of manufacturers of a product. Just sayin'

Btw that bit of advice is tree-fiddy.
 
F
#8 ·
Thinset does not prevent water intrusion. If it did, every tile job would be waterproof. Every basement foundation would be waterproof just because it's thinset of sorts. Learn your product.
.chances are you won't look like a DIY'er asking us to solve your problems. That's why ( as much as I love reading the posts here ) others answer thread questions just like I would. So I keep my mouth shut unless someone hasn't beat me to the answer.

Learn your product, you won't need to ask folks that can't warranty your install.
 
P
#9 ·
Few, I appreciate the comment, but have to say it's about the dumbest thing I have ever heard. Do you honestly think the manufacturer is going to say ANYTHING except that the product works perfectly? I think guys actually using products and learning about them and sharing that with others on sites like this is a great way to learn. So I still would appreciate it if you could explain to me how thinset as a bonding agent for the Kerdi could be waterproof. If you don't know, just say so. I totally understand that most guys just want to get the job done, and when guys like me ask questions they just say that's the way it's done. And that's okay, whatever gets you through the day. But when you throw out crap like just class action them, and use the warranty when it fails is not at all helpful.
 
C
#12 ·
The ditra mat itself is waterproof. Kerdi band over ditra protects against water leaks at the seam. It is not meant to be used for a shower floor that is constantly flooded, that's what kerdi is for. Even if water wicked far enough under the band and got into the seam, it would be able to dry out due to the free space under the mat. If your floor is really going to see that much water, then you should treat it as a shower and use kerdi (or a similar waterproof membrane) and install a drain. In addition, there is a big difference between water spilled on a surface such as a plumbing leak or the conditions in a shower vs. water with head pressure which is how schluter tests their products.
 
B
#14 ·
I can't remember if the Ditra fleece layer is comparable to the Kerdi fleece layer, but I wonder if you would not in fact be better off with a band of Kerdi on the underside of the joint in the Ditra. Given the impervious plastic layer of the Ditra, the fleece might be very different. Don't have a piece with me today to look at. Also, a bit of a pain to install Kerdi underneath it that way, but I understand the fleece to fleece bond with thinset more than the fleece sitting 3/16" above the waterproof level of the Ditra with nothing but thinset in between.

However, I think CarpenterRN has the right idea, it's not meant to stop water with head pressure, just contain water long enough that it has a greater chance of drying to the interior rather than making its way to the subfloor. After all the water isn't flowing through the thinset, it's just seeping, so as long as there isn't a hose turned on it, it's a race between gravity pulling it down and drying action pulling it up.

Overthinking this for sure, use Kerdi for truly wet applications and Ditra for the containing drip and bathtub spillage applications. But an interesting side topic if anyone gets downtime with their Schluter rep.
 
P
#15 ·
Carpenter RN and Nickko, thank you, I understand what you are saying. I guess my confusion stems from the fact that the actual Schluter company videos demonstrate using Kerdi Band with thinset over Ditra on a bathroom floor (not a shower). And in their videos, they use the term "waterproofing", not just water resistant. So if like you guys are saying that it just slows down water penetration and gives it time to dry out, then fair enough, but again I think the perception out there is that it actually waterproofs the bathroom floor. Seems that even with the seams and no Kerdi Band the Ditra would be sufficient for everyday bathroom use, splashing, dripping, etc.
 
N
#16 ·
Yes ditra with no kerdi band would be sufficient for an everyday use bathroom. Before Schluter people used cement board which is not waterproof. I have never used the kerdi band with Ditra. I know someone who did once and he ended up pulling it off because it made a hump.
 
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