Kerdi membrane install question.

[pete c]

I am building a walk in shower. the Sheetrock is up, time to start putting up the Kerdi.

In demo video, they band all corners and lay sheets cut to each wall. Is there any reason I can't use single sheets to go around corners? I understand placing each sheet will be a bit more work, but, it would seem to me that fewer seams is better and also saves a little material. I was wondering if maybe it had to do with the thin set setting up very quickly, allowing little time to fuss with the kerdi.

Or maybe Schluter likes selling Kerdi Band!

[jadnashua]

It's much easier to use smaller sheets than to try to go around a corner. While Kerdi-Band is thinner and makes for a smaller buildup, you can use a band of the Kerdi material...it would depend somewhat on the tile you used whether that would be an issue. The last thing you want is to have the thinset skinning over before you get the last but up. Depending on the wall width, I've also not cut it, run the edge of the sheet around the corner instead of using the band material.

[johnfrwhipple]

Why are you using sheet rock? I would advise you to use cement board in your primary wet zones. Sheet rock or drywall has no business in shower renovation.

Drywall has no business in your shower.

If you want to use drywall why not use Ardex 8+9 over top instead of Kerdi? Then you don't need to struggle with learning to install sheet membranes. Also then you don't have to waste a day trying to find a thinset company that will recommend a thinset to use over drywall in a wet zone.

• Ardex 8+9 is approved over drywall just like Kerdi (if your silly enough to go that route).
  
• Ardex 8+9 is easier to install than Kerdi.
  
• You can flood test your shower faster with Ardex 8+9.
  
• Ardex 8+9 is less expensive than Kerdi.
  
• Ardex 8+9 can easily be applied to the back side (off backer board) a little if you want.

Or you can remove the $25.00 worth of sheet rock drywall up 5'-6' in your shower buy some real backer board (concrete board) - which by the way is approved for use with Kerdi and Ardex and built the shower right.



This is a great application to increase bond strength to drywall. I would only use it in a dry zone.

If your foolish enough to follow the advice of Schluter's or Ardex's marketing teams why not go with the easier approach.

To be fair here is the Kerdi Install video.



If you watch this video listen close to how hard Kerdi is to install. Then look at the drywall. It's not even installed right. Not sure who teaches these guys how to build.

The edges of the drywall or backer board should be screwed off on 4" centres. We screw off the sheets on 6" centers in the field (middle of board).

Watch both video's and ask yourself which is the easier approach.

JW

JW

[pete c]

john, that was my thought as well, but the kerdi dealer says sheetrock is fine. i think it might have to do with the cement board sucking the moisture out of the thinset too quickly.

[johnfrwhipple]

john, that was my thought as well, but the kerdi dealer says sheetrock is fine. i think it might have to do with the cement board sucking the moisture out of the thinset too quickly.

The dealer is selling Kerdi Membrane.

I leave concrete board outside here in vancouver. It gets wet and then drys. Drywall does not hold up well outside. It gets wet and falls apart.

Drywall has no business in a shower. We use concrete board all the time. Never once had a problem. Using drywall with Kerdi is more of a "Sales Tool".

Drywall has no place in your shower renovation.

JW

[jadnashua]

If you install Kerdi properly, the drywall stays as dry as it does in any room. A failure of your plumbing, while always possible, could damage it. But, a failure of your plumbing in any area of the house is problematic. Just do it right, and it should outlast the house.

[johnfrwhipple]

Really Jim? You want to debate the drywall issue again with Kerdi?

Drywall has no business in your shower.

If you want to use drywall why not use Ardex 8+9 over top instead of Kerdi? Then you don't need to struggle with learning to install sheet membranes. Also then you don't have to waste a day trying to find a thinset company that will recommend a thinset to use over drywall in a wet zone.

• Ardex 8+9 is approved over drywall just like Kerdi (if your silly enough to go that route).
  
• Ardex 8+9 is easier to install than Kerdi.
  
• You can flood test your shower faster with Ardex 8+9.
  
• Ardex 8+9 is less expensive than Kerdi.
  
• Ardex 8+9 can easily be applied to the back side (off backer board) a little if you want.

Or you can remove the $25.00 worth of sheet rock drywall up 5'-6' in your shower buy some real backer board (concrete board) - which by the way is approved for use with Kerdi and Ardex and built the shower right.



This is a great application to increase bond strength to drywall. I would only use it in a dry zone.

If your foolish enough to follow the advice of Schluter's or Ardex's marketing teams why not go with the easier approach.

To be fair here is the Kerdi Install video.



If you watch this video listen close to how hard Kerdi is to install. Then look at the drywall. It's not even installed right. Not sure who teaches these guys how to build.

The edges of the drywall or backer board should be screwed off on 4" centres. We screw off the sheets on 6" centers in the field (middle of board).

Watch both video's and ask yourself which is the easier approach.

JW

[jadnashua]

To be fair, almost none of the 'showers' being shown in the demos are real...they're mockup walls and floors, intended to show the application of the membrane, not the structure of the house.

[johnfrwhipple]

To be fair, almost none of the 'showers' being shown in the demos are real...they're mockup walls and floors, intended to show the application of the membrane, not the structure of the house.

Sheetrock in a demo is OK since it is not a real functioning shower. Sheet rock in a shower is a bad idea.

Do be fair - these manufactures should give there head a shake and show some proper structure. Why build a mock up and show it incomplete in the videos? Shows me that the guy building mock ups does just that - build mock ups. But the video is a How to Video - some more care should be shown I think.

Ardex is about 1/3 the price of Kerdi here in Vancouver. A unit of 8+9 in the $70.00 price point and covering nearly 100 square feet. Kerdi sells for $3.00 a square foot almost in most Home Depots.

A 100 square feet at $.70 per square foot is $70.00 - plus the cost of brush and roller (maybe $15.00)

A 100 square feet at $3.00 per square id $300.00 - Plus the cost of thin set (maybe $20.00)


So if Ardex was used in lue of Kerdi over 100 square feet you will be ahead $210.00 here in Vancouver.

I bet the Kerdi dealer did not tell the client this.

NUmber don't lie. First off drywall should not be used - BUT if you go this route to save money, why not save some money?


JW

[johnfrwhipple]

If you use Ardex 8+9 over drywall instead of Kerdi maker sure you order the right miking paddle for the Ardex 8+9.

JW

[DougB]

John,

I'm remodeling a bathroom, with an drop-in tub/shower in an alcove. I'm using cement board. Is there any advantage of using the Ardex product instead of Red Guard or Hydroban?

For the rest of the bathroom, I was planning to use regular drywall, and tile over that. Is tiling over drywall OK? Should I prime the drywall first? What do you do?

[Amish Electrician]

Pete, I don't mean to 'pile on,' but .... NO GYPSUM in the shower! Not even the green or blue stuff!

Yea, I know, various vendors make various claims. Read the fine print. There's a lot of 'maybes' in there. Murphy's Law will ensure that something goes wrong.

I'm not a plumber; I do electric work. Several of my customers are property-management firms, so I get to see plenty of remodel work. I have yet to see a any gypsum product, any tile job, survive.

So, when I do my bath, it will be cement board 100%, even on the ceiling. If nothing else, the cement board won't dent when you hit it with a mop handle. No paper or glue to feed mold, either. Skim coat it with real plaster, and it's as waterproof as steel plate.

FWIW, my walls are getting covered with FRP (fiberglass reinforced plastic) sheeting. Absolutely waterproof, with very few seams - and none of the seams are horizontal. It's that pebbly stuff you see in commercial kitchens and public restrooms.

Maybe I'm over-doing it, but the difference in materials cost is not that much. It amazes me that folks will spend a fortune on getting just the 'right tile,' yet compromise on the basic structure.

[jadnashua]

Kerdi is a waterproof membrane. When it is installed properly, once you protect it with tile, no moisture penetrates it. John is a belt and suspender kind of person. Being in a business where you never want callbacks, it has some merit if people are willing to pay for it. Schluter has paid for an independent testing of Kerdi membrane installed over drywall and it passes all industry specifications for moisture protections IF IT IS INSTALLED PROPERLY. In my 60+ years, I've never had a belt or suspender fail, and have never worn both. You either believe the manufacturer and the testing, or you don't. They do not force you to use drywall, they also list other acceptable materials, which includes cbu. You use what you feel comfortable with and local regulations require. There are thousands and thousands of Kerdi showers in use today applied over drywall that are as dry as the day they were built. If you have a leak, it's either because of poor workmanship or an accidental puncture that occurred after testing and before tile. A leak would require fixing whether it was cbu behind it or drywall whether it was through the membrane or from a plumbing leak behind it. If you don't believe a single layer waterproofer is sufficient, then you'd want cbu on your walls and especially next to your windows in all the rooms of your house, or make the walls poured concrete. A house exposed to rain driver gale and hurricane force winds is a much more hostile environment than a shower. I trust my shingles and paint on the outside of the house to protect the interior walls as I do Kerdi to protect my shower. Feel free to augment it if it makes you feel better. I've got the certification test document somewhere, but you can find a copy on-line if you look. Since the test is only valid for a few years, it gets repeated, and has always passed. Most local inspectors will allow installation to the manufacturer's instructions with that certification. Some won't, and then you do what you have to should you want to use that material. There are lots of choices, pick one you're comfortable with, but installed properly per the manufacturer's instructions, they all work. Some give you more margin for error than others, but if you trust your workmanship and workplace environment to not compromise it, that's somewhat irrelevant. FWIW, in the USA (don't know what the duty is to Canada), you can pick up Kerdi membrane for around $1.75/sq ft fairly easily, including on Amazon. Many places offer free ground shipping. Also, if you believe the websites selling it, list price is in the order of $1.91/sqft. Canada can have some high tariffs on things, so your pricing could vary considerably as well as shipping.

[johnfrwhipple]

Home Depot sells Kerdi for about $3.00 a square foot in Vancouver.

Centanni Tile sells Hydro Ban for about $1.00 per square foot.

Pac Rim sells Ardex for about $.95 a square foot.

Is there any advantage of using the Ardex product instead of Red Guard or Hydroban?

One of the things I like most about the Ardex 8+9 is that it is cementious. My Mapei rep told me nothing sticks better to concrete than concrete. I'm not a fan of the Mapei 315 product but the Ardex 8+9 is really good. Still fine tunning the mixing steps and getting closer to dialling in this product in my installs. I love the Ardex SK mesh for taping. Works like a drywall mesh tape and it's perforated so taping inside and outside corners is easy. Any air bubbles easily removed. I also like that Ardex 8+9 and Kerdi have such a close relationship. Ardex warranities it's installs with Kerdi where as Kerdi does not with things like Hydro Ban and Red Guard. I often find I need to use Kerdi Fix in my builds for things like tub lips, glass work, windows and the like. I do not like using sheet membranes on the walls unless it's a steam shower and do not know a better way of addressing these tough tie in points with anything other than Kerdi Fix.

Kerdi fix bites to eveything I try. Kerdi fix is designed for Kerdi and Kerdi Band. Ardex 8+9 works and is approved for use with Kerdi Band. A pretty simple system with countless options. Mixing is key. Get the right paddle and use a large bucket not a small one. I have two new mixmasters that I will test small batch testing and Ardex just sent me a "Duck Box" to test. Now I can rap up my Ardex testing and hopefully have some better data on the mixing requirements.

For the rest of the bathroom, I was planning to use regular drywall, and tile over that. Is tiling over drywall OK? Should I prime the drywall first? What do you do?




If the Drywall is not in the wet zone or above 6' in a shower (not a steamer) you can use a product call Prim Grip from Mapei as a primer. This is a slick product that preps drywall for tile and makes the surface a little rough so it takes the thinset better. If the drywall has been taped and finished it should be primed with a good drywall primer. Zissner Cover Coat is our number one choice. Once the primer has dried the Mapei Prim Grip is ideal.

A quality thin set will bite to the painted drywall just by itself. The Prim Grip just improves on this.

Each layer in the build relies on the layer before it. If the walls are dusty before priming your dead in the water. Remove any dust residue with a clean 3" paint brush and shop vac. Then prime well, use a roller (A roller creates suction and helps burn any dust left behind into the paint).

Good Luck

[Amish Electrician]

OK, Jad, I won't debate your religion with you.

"IF" is the biggest word in the language. Heck, I'd win the lotto IF I pick the right numbers. IF the Queen had balls, she'd be King.

BTDT.

So go ahead, get by with the minimum possible. I'm confident you also wear Wal-Mart $8 sneakers and drive a Yugo ... after all, they meet all the same regulations as the expensive name brands, so they must be just as good.

While you're fumbling through all that documentation ... I seem to recall seeing somewhere that there were model codes that banned drywall and greenboard from 'wet' areas, like showers- no matter what was over them. You might want to be sure ... and get the permit and inspection as well.

Everything I need to fix in my house is the direct result of someone being 'smarter' than the rule book.