Drywall + Redgard okay for shower?

10 years ago

We are in the process of updating our master bath. My contractor has just installed the backing for the shower tile. He used USG 'Mold Tough' gypsum panels. He has been in business for 15+ years and provided several references.

However, everything I've now read online says that this product is not suitable for wet areas. He did apply Redgard (looks like three coats) over the wallboard. Will the Redgard adequately waterproof the gypsum? I'd rather not ask him to replace the drywall with durock, but if this is going to be a problem down the road, I need to address it now (before the tile is laid).

Thanks

Featured Answer

Tile Corrector

5 years ago

last modified: 5 years ago

This thread died 6 yrs ago

"I'm asking because if anyone would read specs of Greenboard ... it says clearly "This panel also qualifies as a

water-resistant backing board for ceramic tile in residential tub and shower enclosures as permitted in the National Building Code of Canada 9.29.10.4". All you need to do is use waterproof membrane like Kerdi or RedGard. Even if they fail in 20 years tiles will look ugly anyway.""

If you look CLOSE and understand what your reading from CBP redgard (as it is a bit misleading )they also say Cement based gypsum topping. That would mean USG durabond or comparable which is not pictured above.

Taken from the most recent USG greenboard spec sheet.

Avoid exposure to sustained temperatures eceeding 125 °F (52 °C). 2. Avoid exposure to excessive, repetitive or continuous moisture before, during and after installation. Eliminate sources of moisture immediately. 3. Maximum frame spacing for walls is 24 in. OC. Maximum frame spacing for ceilings is 24 in. OC for installations perpendicular to framing and 16 in. OC parallel to framing. 4. Not for use in beam fi re-rated designs. 5. Must be stored off the ground and under cover in accordance with Gypsum Association's Handling and Storage of Gypsum Panel Products (GA-801). 6. Not suitable for use as a substrate for tile in wet areas such as tubs and showers, gang showers and other areas subject to direct water exposure. 7. Use as a tile substrate is limited to tile installed according to the most current TCNA and ANSI specifi cations. Please consult with the adhesive and tile manufacturers for their recommendations for maximum size and weight parameters for use with gypsum board. 8. Not recommended for exterior soffi ts and ceilings which project upwards and away from the building proper. USG Sheetrock® Brand Mold Tough® Panels Firecode® X install and fi nish just like standard.

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Comments (16)

twilkins72
Original Author
10 years ago
Here is a picture of the Redgard.
MongoCT
10 years ago
Here are a few things you can reference:

1) The PDF for RedGard.

Reference 3), Suitable Substrates. There is no mention of any type of gypsum-based wall board being suitable. For clarification, it mentions "gypsum based cement topping" but that is gypcrete, a lightweight concrete-type mix. It is in no way related to gypsum wallboard.

2) I'm no expert on USG gypsum panels. This will probably come across as being a bit negative, but the reason is that they continually change the makeup and name of the different boards, pass them off as being suitable for certain applications, then when they fail 10 years, 25 years, or 20 years down the road, they reformulate the product, rename the panel, and start the game all over again.

I recommend you call USG and ask. I'm fairly certain that the MOLD TOUGH series is considered by the manufacturer as NOT SUITABLE for tub and shower surrounds.

If USG doesn't say that they are not suitable, but defers to TCNA standards, then they are not suitable.

In my world? It's not suitable. I'm a basics kind of guy. Cement board. Wonderboard or Durock in wet areas.

Good luck with your project.

USG contact info: for technical assistance please contact 1-800-USG4YOU (874-4968)
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With a curbless shower, I see two issues you may be facing. If he is planning on using a traditional rubber liner, a pre-slope under the liner is required. This slope is a minimum if 1/4" per foot from the drain to the farthest wall. In this case, I assume that to be the entry. I fugure that to be about 2 3/4" higher at the entry than at the drain. The rubber or vinyl liner sits on this and a FINAL mudbed is then formed over the liner. As you can see, there will be issues with no curb and how you'll terminate the slope to a feather edge at the entry. I don't see how that can be done. The other issue is with the liner itself. I see no way to attach it to a mudbed that would have to end at a feather edge. These liners are designed to go UP the vertical walls about 6-8" and nailed into place. Having built these before, scrap the liner and use the Kerdi. It's a bulletproof install, you only need ONE mudbed as the material is bonded directly to the mud and you can generally extend the Kerdi six or eight inches into the bathroom for a bit more insurance. On one hand, yes...it's a bit more cost, but realistically, it's also a shower you'll probably never need to repair or replace. The Kerdi is under $1.40 sq/ft. Their drain will run about a hundred bucks. On the other hand, you only have the cost of one mudbed, you eleminate the vinyl liner, as Kerdi is completely waterproof, you can save by using standard drywall in the shower as opposed to cement board. This is what Schluter recommends. Bottom line is that you'll pay a little more but get a far superior shower. If your tile installer isn't comfortable or familiar with Kerdi, find one that is. Here is a link that might be useful: Kerdi Shower Handbook
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Your contractor will not want to hear all this and will push back telling you that it‘ll be fine, he’s never had a call back, and he’s done it like this forever. But you should have a meeting. Ask him what all the waterproofing steps were and take notes. Post what he says here. It helps if you have more in-progress photos. Document all the notes from your meeting by summarizing and following up with an email to the contractor. If it’s not waterproofed right, no sealing or caulking that you do will change that for the long term.
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Update: The contractor has installed the dennshield as tile backer board ( I request dennshield instead of cement board in order to fulfill fire rating) The below picture shows the whole view: Joseph asked me if the walls are right angle. I tried it with a tile and could see that "no". I compare the depth of the both side of the black plastic plate of the valve. I put a 1/2 inch drywall next to the valve to simulate the condition after tile. The shower outlet below the valve is tilted to the right while the valve itself tilted to the left. Also, the grey denshield installed on the shower head side does not flush with the existing drywall on the top. One more thing, I could feel a nail lying underneath the waterproof liner of the shower pan. I asked if the nail will puncture the liner in the future, the contractor said no, as there will be mortar on top of the liner and the mortar will shape into the nail and there will be no pressure which make the nail puncture the liner. The electric outlet
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User
10 years ago
No, it's not an appropriate substrate. Just because he's been doing it that way for 15 years doesn't mean that he's been doing it right. It should be ripped out, and replaced with a cement board substrate.
StoneTech
10 years ago
If it meets ANSI 118.10 standards for a "Surface Applied Membrane," you should be good to go.(and I believe it does) Three applications ought to be adequate.
twilkins72
Original Author
10 years ago
Thank you very much for your input.

If I ask him to replace the drywall with Durock, can he do so without removing the new shower pan? The pan was done properly and floor tile has already been installed over the pan.

Another option I thought of is to request another coat of Redgard or for Kerdi to be applied over the Redgard. I'm not sure how effective this will be where the walls meet the floor, which is where I assume most problems occur.
proxus
5 years ago
Out of curiosity....Did he replaced Greenboard with Durock? I'm asking because if anyone would read specs of Greenboard ... it says clearly "This panel also qualifies as a

water-resistant backing board for ceramic tile in residential tub and shower enclosures as permitted in the National Building Code of Canada 9.29.10.4". All you need to do is use waterproof membrane like Kerdi or RedGard. Even if they fail in 20 years tiles will look ugly anyway.
proxus
5 years ago
sure but as you quoted:

"Not suitable for use as a substrate for tile in wet areas such as tubs and showers, gang showers and other areas subject to direct water exposure"

There is no direct water exposure when board is properly sealed. RedGard waterproofing is 0.6 MPa so properly applied coats shouldn't leak any water.

You could easily multi-coat as this guy did:
Mr. Memes
5 years ago
It doesn't matter after you apply the coats of regard what substrate your using. Today's gen is quick to throw the tcna handbook at you cuz they don't understand or see the real working picture.
Regards when applied correctly is a waterproof liquid membrane no air no water will pass so that being said definitely no thinset will pass either.
The only judgement here could possibly be the greenboard moving with the Weight of the tiles on it. But that’s why you have to apply even more redgard to the seams.
PRO
The Kitchen Abode Ltd.
5 years ago
"It doesn't matter after you apply the coats of regard what substrate your using."

In correct, it does matter according to building codes. Within the wet zone these types of products are not permitted to be used as a substrate to support the application of tile. Regardless of the applied waterproofing membrane the supporting backerboard must meet specific performance requirements of which a minimal level of water resistance is required amongst other requirements.
Mr. Memes
5 years ago
Well maybe I should become a kitchen designer this way I’ll automatically know all there is to know about waterproof substrates tile and how bathrooms are made.
PRO
The Kitchen Abode Ltd.
5 years ago
Maybe you should take more care in your advice and how you word things. It is inappropriate to make statements that are fundamentally incorrect and by making such it is evident that your understanding of building codes, materials and their application is severely limited.

The comment you made concerning the fact that it does not matter what type of material is utilized as a tile backer board in wet zones because the applied waterproofing prevents the tile backer board from water exposure is clear evidence that you do not understand all of the related issues and the reasoning behind the building code requirements.

This does not mean you can't express your opinion, it's just that when doing so you should be clear that it is just your opinion versus implying it as factual.
Mr. Memes
5 years ago
Your from Canada I’m from New York you can do the math. There maybe building codes for your area but in the state there next to none for redoing finishing walls with tile.
PRO
The Kitchen Abode Ltd.
5 years ago
Not sure what math I need to do.

You may not be looking at the appropriate code(s). If you are in the city of New York you will most likely need to refer to 3 codes in order to fully understand all requirements. Suggest starting with the IBC as this has been accepted by many regions as the fundamental building code for which other state and city codes are based upon.
Tile Corrector
5 years ago
last modified: 5 years ago
" It doesn't matter after you apply the coats of regard what substrate your using "

100% innacurate , not true.
User
5 years ago
I'll bet that someone doesn't even know what a mil gauge is, much less own one.

Drywall + Redgard okay for shower?

Tile Corrector

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Drywall + Redgard okay for shower?

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