Can I Use Any Thin Set With Kerdi? The ICC-ES Evaluation Report On Kerdi Says You Can

[johnfrwhipple]

Thanks Jim.

So the primer is used for self leveling applications over concrete and plywood subfloors. I thought Dale was suggesting the "Ad-mix" products that make a non-modified thin set "Modified". I'm trying out a bunch of my stock here in Vancouver to see what works best.



Here is a current fireplace build i'm working on.

You can see the Hardie Backer installed around the fireplace. The dust from Hardi Backer is not good for you so keep it clean and where a mask. Working with a mask sucks all day. I like to clean the Hardie backer and then prime it with a diluted "Ad-Mix". Here you can see a mix one part Grani Rapid liquid and 4 parts water. We set the Italian Marble with Grani Rapid so all liquids are compatible.
Less dust and a killer bond. With any fireplace build heat and expansion are issues. For this reason a S2 thinset is ideal in my book. The best of the best - Mapei's Grani Rapid.

My first test was the "Ad-mix" from Mapei for Grani Rapid. This stuff is sticky and I thought I would start with the best and work down from there. I would think that the product from Mapei would great priming drywall for thinset. I would also think that then using Grani Rapid would make the best bond. Likewise using the "Ad-Mix" from Laticrete for their 317 floor and wall dry set mortar as a primer and then a batch of 317 with the ad-mix must be considerable stronger than just dry set.





Here I tested Grani Rapid "Ad-mix" over plywood. I do a lot of custom drywall work when building my features and have always had access to a product called "Guardz" - it is since stop selling locally and this discussion of latex primers over drywall spiked my curousity about a thin set "ad-mix" and Guardz being one in the same. Both are watery products. Both are sticky on the hands. Both are milky white. Hmmmm.

The following day the mesh tape was so-so. I ripped it out.

The waterproofing mat or fleece with the Grani was pretty good - but not perfect. I ripped it out. I think soaking this product in the ad-mix and giving it two days to cure might just work.

The hands down winner was the paper drywall tape. The stuff was stuck like a mother and even 100 grit sand paper had a hard time removing it. I then set regular corner beads inside and outside over the Grani Admix.



I love the inside and outside "Pro Beads" - these install just with "Joint Compound" which is a regular drywall compound with some glue. The glue makes it stick better and bite harder - just like modified thin set does compared to non-modified thin set.



Last week I did call my local reps and asked about Kerdi over drywall. My Mapei rep did not recommend one particular primer for use with Kerdi but did tell me that drywall in a shower is not acceptable. I did ask my Laticrete rep what they recommend for use with Kerdi over drywall and he recommended not using drywall in the shower. Hmmmm.

Seems for the most part here in Vancouver anyone in the business recommends anything but drywall in the shower. Even Dale mentions that Kerdi is acceptable over other backer boards and that is why they list them. Dale does not recommend drywall for shower curbs as well.


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Jim I'll pick up some self levelling primer and put it head to head against Grani Rapid from Mapei.

Maybe I'll set a shelf on top of the Kerdi and see which holds more weight.

JW

[jadnashua]

Remember, concrete products are at their rated strength after 28-days. The required shear strength of the bond to Kerdi is 50psi, but it tests out at 75psi. Real uses don't have huge cantelevered loads, only shear. On a tiled wall, any local load is shared by the adjacent tile since they are tied together with grout on a vertical load (shear), but a much less tenacious situation in tension.

I haven't received any official response from anyone yet, but it appears that the primer should provide all implied requirements - it's laytex based to prevent moisture migration and it is compatible to concrete based bonding to anchor the thinset. We'll see what the makers really think.

Best practice is to not use drywall mud in an area that is going to be tiled, regardless of what is going over it, Kerdi, or just tile (say in a backsplash).

[johnfrwhipple]

Remember, concrete products are at their rated strength after 28-days. The required shear strength of the bond to Kerdi is 50psi, but it tests out at 75psi. Real uses don't have huge cantelevered loads, only shear. On a tiled wall, any local load is shared by the adjacent tile since they are tied together with grout on a vertical load (shear), but a much less tenacious situation in tension.

I haven't received any official response from anyone yet, but it appears that the primer should provide all implied requirements - it's laytex based to prevent moisture migration and it is compatible to concrete based bonding to anchor the thinset. We'll see what the makers really think.

Best practice is to not use drywall mud in an area that is going to be tiled, regardless of what is going over it, Kerdi, or just tile (say in a backsplash).

This info will help with Denshield installs as well. Many drywall crews get the job of boarding a shower and so many times we show up and the drywaller has mudded out the Denshield.

With Denshield we normally just wet the area if the priming is not allready done and scrape away the drywall compound. With drywall and mud this weakens the paper and we do not do this. With Denshield it has never been a problem.

I like the "Ad-Mix primer" over the substrate therory. "Ad-Mix" over any substrate increases bond strength and slows the absorbotion of liquid out of the setting material into the backer board.

This use of "Ad-Mix" might also make the installation of Kerdi, Dal Seal and Noble Seal TS easier over any substrate. Especially if a dyrset mortar is being used.

[pitterpat]

1st, Schluter says that drywall is ok, look here, http://www.schluter.com/media/ShowerHandbook.pdf Schluter Shower Handbook, pg 7.

2nd, no primer and no drywall mud. If it bubbles, flakes or peels off then your Kerdi loses it's bond and no waterproofing. Also if the drywallers have been sanding in the area then you need to brush down then wipe down the drywall in the area that the Kerdi will be installed with a damp cloth to get rid of all of the drywall dust. Dust means there is a chance of poor Kerdi adhesion.

[johnfrwhipple]

Pat did you know that the Kerdi handbook says to use a latex primer over drywall in the Q&A section?

What primer do you use?

I see Jim helped you out seven years ago. Jim has over 6,000 posts on John's site and you over 2,000 posts. Have you come to shed light on installs or to help out you buddy from the John Bridge site?

http://www.johnbridge.com/vbulletin/...ad.php?t=18293

Pat is this where you first met Jim? So you have been building showers for seven years in Indianapolis? Have you worked for Christopher Wright from Wrightworks?

Seven years ago you asked this on the John Bridge tile forum "Removing ceramic tile from concrete floor

--------------------------------------------------------------------------------

I've searched the forum and read some of the demo threads. My question is this:
1. For a small bathroom floor 4 x 5 is it worth renting the demo hammer? (Bosch)
2. How much mess does it make? I already made a huge mess and feel guilty

3. And will it take up the mortar enough to have depth to pour SLC? There is black mastic or thinset(?) under the tile. Who ever did this tile job did not ck to see if the 12 x 12's were adhering. One of the tiles I took up whole and it did not have a speck of adhesive on it.

TKS, Pat " http://www.johnbridge.com/vbulletin/...ad.php?t=16105

Pretty clear to me from this post you are learning as you go. That's OK. But seven years later you are going to school me on building showers? My demo hammer is a dewalt 1" it's older than your question.

[jadnashua]

The point is, don't use drywall compound on the nails/screws or seams when using Kerdi. If you do, then you should treat it as specified. The way you write it, you imply that it is required all the time, and this is patently false. this is all part of being professional...following the manufacturer's instructions and the approved method, whatever system you choose.

[johnfrwhipple]

The point is, don't use drywall compound on the nails/screws or seams when using Kerdi. If you do, then you should treat it as specified. The way you write it, you imply that it is required all the time, and this is patently false. this is all part of being professional...following the manufacturer's instructions and the approved method, whatever system you choose.

Jim the manufacture has no specification for dry wall compound. Do you not find it odd they do not specify an exact product? Some Advice I got from the NTCA was anytime you do a project with drywall in a shower is to document the process and get the manufacture involved.

As the biggest Kerdi pusher I know Jim you don't even know what primer to suggest and are scrambling to find a answer.

I would think that in the future I will specify removing any drywall that is covered with drywall compound and replacing it with drywall with no drywall compound. This way you will have no warranty issues and by doing so be following all the manufactures guidelines.

The Kerdi Handbook in the Q&A section recommends a latex primer. Which one Jim?

JW

[jadnashua]

If you're doing this yourself, don't use drywall compound. If it ends up there, then search out the necessary fixes to your mistakes. If it was only over screws/nails, I wouldn't worry about it, as if it did get soft, it would reharden and the areas around it would bond well with the thinset. I'd only worry about it if it was a large area like say a seam where it could be as much as 12" across with the mud and likely thicker than over just a screw hole dimple. Primer over drywall is for a mistake in the installation, it should not be the primary issue during an install.

[johnfrwhipple]

If you're doing this yourself, don't use drywall compound. If it ends up there, then search out the necessary fixes to your mistakes....

Jim your the local Kerdi expert and you don't even know the answer. That's funny.

I spoke to the top Schluter rep and he wouldn't even give me a specific product.

Here is my question to Dale.

John "Can you sent me sent me list of recommended primers for priming drywall to be covered with Kerdi?"

And Dale's response to me:

Dale "We sot like to be proprietary but both Custom and Mapie have latex primers that would be suitable. They may indicate for use only in dry areas which once the Kerdi is applied the drywall will never see a drop of water."

So I guess it is on me to figure it out??? Doesn't give me a warm fuzzy feeling inside.

Remember Jim when I asked my Mapei rep he did not recommend drywall in showers. So I guess it is all on Custom to save the day. I'll call them this week and speak with my rep Dave Shirley and ask him which latex primer they recommend to prime drywall for a Schluter Kerdi install.

I think if any drywall compound is used it is best to just rip it out and put up fresh board. That way your safe and covered by the Schluter warranty - otherwise you can send Schluter an email stating the product you wish to use and let them answer yes or no.

I will submit my test results to Schluter and once done ask permission to use the product I find to work the best. Until then I think the only safe thing to do is rip out any drywall that has drywall compound on it.

Right Jim? Hell if you don't know what to use and you have been selling Kerdi for seven years who does? Maybe John Bridge knows. Jim did you ask John Bridge? Did you ask CX? What did they say?




If your using drywall and Kerdi remember that in Vancouver it is not allowed. The TTMAC does not endorse it. The NTCA does not endorse it. The TCNA removed it from their current spec book. The ANSI does not endorse it. The Gypsum association does not endorse it. And the most amazing point is that Schluter has no recommended product they can edorse with any mudded out drywall surface. Makes you wonder if this is such a good idea???

[jadnashua]

I have to ask, as you indicated you've installed Kerdi for years, what did you do in these circumstances when drywall mud was there? My training said not to use it, I haven't, and therefore haven't run into that situation. I never claim to know all the answers...I do know how to do it per the manufacturer's instructions, and that's the way I've done it. That's also the way I guide people...the way the manufacturer says they've tested it and it works.

The TCNA handbook never calls out specific products, only classes of products, but I see under Shower Receptors method B422-11, which appears to be the same as B422-09, which appears to be the same as B422-07, depending on which year's book you're looking at. You don't have to be a rocket scientist to infer they're talking about Kerdi in that method of approved, tested install.

[johnfrwhipple]

I have to ask, as you indicated you've installed Kerdi for years, what did you do in these circumstances when drywall mud was there? My training said not to use it, I haven't, and therefore haven't run into that situation. I never claim to know all the answers...I do know how to do it per the manufacturer's instructions, and that's the way I've done it. That's also the way I guide people...the way the manufacturer says they've tested it and it works.

The TCNA handbook never calls out specific products, only classes of products, but I see under Shower Receptors method B422-11, which appears to be the same as B422-09, which appears to be the same as B422-07, depending on which year's book you're looking at. You don't have to be a rocket scientist to infer they're talking about Kerdi in that method of approved, tested install.

Jim I never had to deal with drywall compound before when I was installing Kerdi. For the most part back then I was a Custom Boy doing Red Guard and Wonder Board and leaving my clients with the reciepts and a 25 year warranty. Then read about Kerdi online and took the course. After that I offered Kerdi or Red Guard. Since I never trusted a thin set seem from day one I always Red Guarded my seams - I wish I knew Schluter doesn't warranty that install back when I did it.

Now in Vancouver you need a Schluter Workshop Card to install Kerdi. No drywall.

I always used cement board or Hardie Board. Loads of Denshield and now my preference is Green EBoard, Super Panel (concrete board) or Hardi Board.

These debates with you have shed the light onto the drywall compound. The fact you push drywall on people to sell Kerdi has ramped up my efforts to show people what a poor building practice this is.

Jim I'm sure in your perfect world drywall is OK. But construction should offer up a little fudge factor. A perfect kerdi shower might not leak, but it could easly rot out from the back side. No one is perfect. This is why we test shower pans. If we could test walls we would.

To promote the use of drywall just to sell a product is reckless. Do you not want to help people build a better bathroom. I'm trying to reduce landfill waste. I have three little girls. It would be nice if construction was not disposable. It would be nice if my kids don't have to deal with your garbage and your kids not to deal with mine.

It would be nice if things whee built to last.

It would be nice if you are going to push Kerdi on every thread you stop promoting drywall as a sales method. Your part of the problem I'm fighting. I'm 44. I build showers every week. I'm not going no where.

I have help so many people build their own showers. Through emails. Through web pages. Right here on Terry's sight and others.

The new DIYer wants to build better. They are tired of paying top dollar for Shit.

JW

[jadnashua]

They specify at LEAST a 2" overlap of the seams to account for minor errors to protect the SYSTEM. The narrowest Kerdi-band is 5" (you can get wider, if you wish), so you've got to be a little careful with your seams, but if you can put up wallpaper, with a little practice, you can put up Kerdi. Use whichever approved backer that makes you feel comfortable. With any product, if you don't maintain at least some level of craftsmanship, it could fail. Personally, the thinner material is a plus: it's easier to see if it is embedded properly and minimizes buildup. Plus, it folds easier to get squarer corners. Any surface membrane is a step up from a conventional shower and provides more flexibility in design and options. Kerdi is only one of those available. It happens to be one I've used and been trained on, and found to be functional.

[johnfrwhipple]

What does your post have to do with this thread.

You asked about drywall compound and now are talking about overlapping seams???

Thinner is not better.

Thinner is cheaper.

Thinner is lighter.

Thinner makes for smaller rolls.

Thinner rolls pack tighter in containers.

You mention with a little practice you can get the hang of it. That is for sure. Learning Kerdi I did rip out a lot of product those first few installs.

My biggest mistake was cleaning the product before tiling. In the handbook it says you can install and tile right away. We did our second project with Kerdi and set all the Kerdi day one. Took me 8 hours with a helper to do a 4'x4' shower and a 4'x3' landing area. Next day I go to set the floor tile and bring out the shop vacum and suck the Kerdi right off the floor. Turns out I'm told by local rep I didn't let the thin set set up long enough or the setting material was bad. Now correct me if I'm wrong but you are suppose to check coverage rates when tiling. When you pull a tile up it creates suction. This scares the BJesus out of me with dryset mortar and a membrane. Bond breaker. Bond Breaker. Bond Breaker.

That is one of the things I love about rapid setting thin set for these membrane installs. The next day you can clean up the place and not worry about sucking up the Kerdi in the shop vac hose.

Now we learn that Kerdi needs a latex primer over drywall compound. Again Jim if you are around any jobsite the use of drywall compound is everywhere. Here in lies the difference between you and I. I work for a living and you type for fun. I promote all products that I have success with and you promote just one. You never even worked in this industry but you pass yourself off as the local expert.

Your a salesman Jim. And doing a dis service to many with your short sighted promotion of one product a few of your retired buddies love.

How many showers have you built again. It is four right. Any pictures of your work. Any pictures of your redguard work you can share. Any insight other than reposted Kerdi manual stuff. To tell people a little practice is needed is crazy.

Just practice on your shower. Maybe you do it right. Maybe it holds water. Maybe it won't fail. Maybe people should look harder into who is giving out the information they are reading online.

[johnfrwhipple]

Yesterday I called on Custom Building Products (1 800 272 8786) and spoke to Tom in the Technical Help Department. Tom was very helpful and answered all my questions.

I asked Tom what 'latex primer' Custom Building Products recommends for priming drywall compound before installing Kerdi membrane. Tom said first that Custom Does not recommend drywall in a shower so he could recommend nothing. I told Tom that I was told by Dale Kempster at Schluter that Custom and Mapei both have primers that can work but I was not sure which one to use.

Tom explained to me that most of the primers are 25% solids and 75% water. He said that the water can reaactived the drywall compound and cause a bond breaker scenerio.

Tom went on to explain that he has seen commercial projects in his travels that the contractor made a mistake of having the dywall skimmed out and all the drywall needed to be removed. Tom said not to use white drywall, regular drywall, green drywall or purple drywall in a shower. He went on to say why not use our cement board and redguard and you will get a 25 year warranty. Good point Tom.

So todate Mapei, Laticrete and Custom Building Products all have told me not to use drywall in a shower.

The NTCA, TCNA, ANSI and TTMAC do not want drywall in a shower.

Vancouver building inspectors do not want drywall in a shower

But Schluter recommends drywall in a shower. By drywall they mean just the drywall but not the drywall compound. If the drywall has compound on it your screwed because there is no product that Schluter can recommend for you.

What do you do???

I thought about asking a paint expert and I picked up some 'latex primer' from my paint supplier. My old go to "Guardz" product no longer available to me so I'll try out a few more.

Now you have to ask yourself I think why Schluter and Jim here on Terry's site recommend drywall at all. If no one else wants it in the shower (including the Gypsum org itself) why do they promote it? Could it be because it is easy. Cheap. Fast. Is that not what you want to hear when searching the proper way to build a shower.

When your at the box store do you want to hear that you need a diamond wheel and 4" angle grinder to cut the cement board. Or do you want to hear that with this product you can just use drywall and cut it with a pocket knife? So by endorsing and promoting drywall are you selling a system that is good for your home or are you selling against every other product since no one else will endorse or warranty it? If you use drywall in your shower know the risks and ask Schluter (in writing) to tell you exactly what products to use to install it.

You see the thinset companies do not list Gypsum in shower locations as an acceptable backer. And Schluter does not make a primer they recommend. In fact both companies they recommended as a primer source said to me "No".

Hmmm.

[jadnashua]

Commercial verses DIY'er often run into different things. A DIY'er, if he's smart, reads the instructions. If so, and this is a remodel, there's no drywall mud in his shower because he put it up. If he installs things right, the shower doesn't leak, the drywall stays dry, everything works. Over drywall, unprimed, no mud, assuming you wait the 24-hours they recommend when doing a flood test, the sheet is adhered pretty well and probably better than with a modified. Yes, a modified has better initial tack and ultimate strength, but if it isn't embedded into the fleece well, it could easily end up being weaker than a proper dryset installed properly. And, where you're talking about TONS of pull required to break the bond with either dryset or modified, why not use a dryset? When installing the Kerdi, they recommend you peel back some to verify that it is properly embedded into the thinset. A dryset flows better than the sticker modified thinsets and gets into the fleece better rather than just sticking to its surface. If you verify this as you go, the stuff is quite tenacious. Just like you can peel tape off if you pull it at a steep angle, you have lots more trouble pulling it off in tension. you can tell if you have a good bond by looking at the membrane.

When the membrane is sandwiched between two rigid surfaces, the backer material and the tile, it is protected and thickness is somewhat irrelevant. Goretex (TM) is very thin, but works, and you never see it as a surface treatment. It really isn't very hard to protect it during construction - you'd want to protect any membrane, either painted on or sheet, and what you do for one will work for the other. And, it's quite easy to do most of the walls and tile before you even start to lay the pan. Leave the last row or two out at the bottom, and you can install the pan, install the membrane with the required overlaps, and there's little opportunity to drop tools on it or mess it up while working on the walls since they're already done!

The TCNA does list gypsum board as an acceptable backer material in the TCNA handbook in the section where they describe sheet membrane shower construction.

If it took you that long to do your first shower with Kerdi, I feel sorry for you. It really isn't that hard. Some research beforehand should have prepared you to do it right the first time in much less time. The video in the box with the drain also available on-line is pretty good if you can't get a class. It took me about the first sheet to get the hang of it, and the rest was easy, and for a type A personality, that's saying something! I've mellowed some as I have aged.

ANY system takes a little practice. I think it's tougher to paint on nice, even layers of waterproofing, achieving the required min/max thickensses without getting some pooling or drips that can come back to haunt you when you get ready to set your tile; or, get more buildup in a corner. Thicker sheet membranes also have buildup issues.

Drywall is stong enough, stable enough, and easily workable for the majority of walls in homes installed in the USA and probably Canada. They hold tile quite well in dry areas, and, if kept dry by a properly installed membrane, do an equally good job in wet areas (therefore, not really wet). If using a different backer makes you feel safer, use it, but it works, has worked, and will continue to work, when installed properly.

All of those people have a liability problem you've talked to, and I fully agree - drywall should not be in a wet area. The main issue is, if you install a Kerdi shower properly, the drywall is NOT in a wet area. There will always be a yahoo that never reads instructions, slaps something together, then blames it on the product. If your shower leaks, regardless of the material it is made out of, you'll likely have problems. It's just a function of time and severity.

With non-setting drywall mud, it doesn't magically fall off the wall if it gets wetted - well, maybe if you used a high volume or pressure hose, that's not the same as brushing or rolling some onto it. Even if the sealer contains some water, once it dries, everything drys out, and then protects the stuff underlying it from getting wet again. You should not cover the primer until it has properly cured - again, read the instructions on how long to wait after installing. Fail that, just like anything, the results are unpredictable.