kerdi membrane

[SILVERWOOD]

I was told to use non modified thin set with schluter kerdi membrane, such as masterblend or hydrolisis may result. I don't like non modified thin set, it's not very sticky and the open time is shorter. The first time I installed kerdi was on a shower ceiling. It was already drywalled so I bought a piece just to cover about 16sf, I applied it and the limestone over it with full flex. It does not seem to be a problem(two years and counting). Anyone else out there using kerdi, does a little bit of latex modified thin set really comprimise anything?

[David Meiland]

Re: kerdi membrane

According to John Bridge you can use Versabond, which is modified but not highly so. Apparently the highly modified materials will not cure because the membrane does not absorb any moisture, whereas typical CBU or mortar beds do. Bear in mind that you need to follow the instructions to have a warranty. I am about to do my first Kerdi install and will use Versabond because of the reasons you mention.

[JazMan]

Re: kerdi membrane

Schluter recommends using unmodified thinset to install tile over Ditra and Kerdi because of the difference on how the two types of thinsets dry. Modified thinsets require air to set up, where as unmodified will set up due to chemical reaction. This is important because once covered with tiles, Schluter feels that modified thinset may take a long time to dry since it's sandwiched between two impervious layers. It also gives Schluter a selling point of recommending the cheaper unmodified mortars for all tiles including porcelain which require modified thinset when installed over any other surface.

Because of the confussion and because they saw an apportunity, Schluter granted license for Hydroment to market Ditra Set Mortar. If available in your location I recommend it since it is just right for these types of installations and works well. So, use Ditra Set to install any tile over Ditra or Kerdi. Use whatever thinset is appropriate for the substrate to install either product to the substrate, including Ditra Set if an unmodified thinset is called for.

Jaz

[inkster]

Re: kerdi membrane

unless your planning on calling John Bridge if there is a problem ,and he's providing the warrenty who cares what someone other then the mfg. has to say..The real problem is which Mfg...The Thin Set folks say use Mod. Schluter says unmod...your caught in the middle sounds to me! I would use Elmers Glue! but like Mr. Bridge dont call me! :smile face:

[David Meiland]

Re: kerdi membrane

OK... that's real helpful...

[Kgphoto]

Re: kerdi membrane

I guess it comes down to whether or not you take the advice of someone who has worked with the product and the company and even written a book about this one subject(The Kerdi Shower book) and follow it.

I have done a only a couple of Kerdi Showers and some Denshield showers and not one of them have had any kind of failure or mold and mildew. The oldest is 10 years old. Of course I almost always install a bathrrom exhaust fan at the same time.

I used the unmodified thinset and it held everything fine and it all went without a hitch. I think I would trust John's judgment as Kerdi won't reinstall the product, just supply new and that is a pretty small part of the cost of the project, so it you have emperical data, and can get the installation details right, I say, go ahead with versabond, if you can't bring yourself to use unmodified. I would also recommend adding a fan to the mix to help it dry out between the steps. It is more important to use unmodified behind the kerdi, than under the tiles, especially if the tiles are small and there are a lot of grout lines. 12x12's I would be more inclined to use the Kerdi recommended product, but John hasn't had any problems and he does/did lots of showers.

[mbyrne]

Re: kerdi membrane

Even though John Bridge was paid by Schluter to write his book, I don't think John will pay for repairs when any of his readers don't follow SCHLUTER instructions.

Can anybody explain to me why--in light of an overwhelming number of free 800 technical service lines--most construction workers seem totally unwilling to make that free call to get advise from the horse's mouth? Can anyone also explain why-after receiving conflicting information from a non-manufacturer--most almost invariably choose to follow the unauthorized advice?

Even in court--as they go down in flames--errant construction workers still cling to the idea that "Uncle Bob" knows better than the manufacturer.

I have tried to fight the idea that the US has, is, and continues to dumb down, but I just do not know anymore.

[inkster]

Re: kerdi membrane

I AGREE WITH THAT! Not only will "Uncle Bob" or who ever not pay, neither will the MFG..If it does'nt follow their directions -no ones on the hook! Except for the installer !

[not-the-inspector]

Re: kerdi membrane

Even though John Bridge was paid by Schluter to write his book, I don't think John will pay for repairs when any of his readers don't follow SCHLUTER instructions.

Can anybody explain to me why--in light of an overwhelming number of free 800 technical service lines--most construction workers seem totally unwilling to make that free call to get advise from the horse's mouth? Can anyone also explain why-after receiving conflicting information from a non-manufacturer--most almost invariably choose to follow the unauthorized advice?

Even in court--as they go down in flames--errant construction workers still cling to the idea that "Uncle Bob" knows better than the manufacturer.

I have tried to fight the idea that the US has, is, and continues to dumb down, but I just do not know anymore.

I dont believe there will be much competition in our line of work for a long time to come from what I've seen. At least not from americans.

[Kgphoto]

Re: kerdi membrane

mbyrne,

I guess my point is that most manufacturers don't pay for repairs or not much of the total cost, with the possible exception of Custom Building products, so even if code allows green board, we don't use it. Even if unmodified is called for, if sleightly modified works a little better we do use it. Even manufacturers once called for green board, so how could they ever be wrong? (drip drip) (that was sarcasm).

I don't recommend going to uncle bob unless uncle bob has years of experience doing it right and making corrections and can revisit his sites and see the long term results of his efforts. Or "uncle bob" is John Bridge and Michael Byrne. Now if both Uncle Bob's have conflicting opinions, then ya gotta choose somehow.

[JazMan]

Re: kerdi membrane

I don't think it was necessary to bring John Bridge into this thread. John is not the "Guru" of Kerdi, Schluter is. Having said that let me mention that I respect and like John very much. I first ran into him when I joined InfoTile almost 6 years ago. Later he formed his own forum which has become an unbelievable place that I visit daily. This April I had the pleasure of speaking with him and also Dave Gobis at Coverings. John is one of the most respected tilesetter and author in our industry.

Something I don't understand though, is why Schluter eventually relented and agreed to finance his Kerdi book even though he couldn't be convinced that unmodified mortar was the best choice over their membranes. We all know that Schluter had tested for years and concluded that using modified thinsets to install tiles over Ditra and Kerdi could be problematic and were not necessary. Maybe the small controversy created more demand for both Kerdi and the book? (nahhh)

I do understand John's reasoning, I think that he has a hard time trusting unmodified thinset to set porcelain tile (me too sometimes) and feels that using a modified mortar will not hurt. So just to be on the safe side he has concluded that using a lightly fortified (cheap) thinset is what he will use. He always tell us that if you do go against Schluter's directions that you are on your own if something goes wrong. I don't think he has ever said that slightly modified works a little better, just that he doesn't think it'll hurt. What he did say recently is that he recommends using Ditra Set if available where you live. (something I have been saying since I first heard of it and then later saw at Surfaces last Feb. '06 in Las Vegas.

There are many other 'lightly modified' thinset besides VersaBond, he recommends it because it is found at all (?) HD stores and because they advertise on his site. No problem with that since there are HD store everywhere.

Jaz

[dgbldr]

Re: kerdi membrane

Jaz,

There is something a bit unclear about Schluter's motives. I can understand the concept of curing modified vs. unmodified. However, if you look at the data sheet for a membrane like Redgard, you will see they recommend modified. Why is it that a liquid membrane should cure/breathe any different than Kerdi?

I'm guessing Schluter knows that Kerdi sticks to unmodified better than it does to modified and their recommendation is based on that. And I don't doubt it.

On the other hand, when a tile manufacturer recommends modified for their tile, I don't doubt it either. So we have a conflict.

Until that conflict is resolved, I will only use tile and membrane that happen to BOTH have the same recommended thinset.

DG

[John Bridge]

Re: kerdi membrane

The debate over which thin set to use with Ditra and Kerdi rages. I don't know that it will ever go away. Since I've been brought into this, though, I would like to clarify a couple points.

First, I was not paid by Schluter to write The Kerdi Shower Book. I included Schluter in the final editing process, though, and changed a few things to suit them. The book is mine: not Schluter's, and I have posted notices to that effect.

Tile Your World (2003), on the other hand, was financed by Schluter. Their support allowed me to become a publisher, and I'll be forever grateful.

It's true I use Versa Bond in places where Schluter doesn't approve, but every time I mention it in public I remind people that Schluter doesn't like it, and that they would prefer the use of dry set mortar. So it's not exactly like I'm subverting Schluter's instructions.

Please don't respond to me here. I don't get over here often.

P.S. Who the hell is Uncle Bob? :)

[John Bridge]

Re: kerdi membrane

Sorry for the extra thead. Don't know how to work this board. :)

[mbyrne]

Re: kerdi membrane

That's alright, John--some people think I don't either!