Drywall + Redgard okay for shower?

twilkins72June 8, 2013

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).


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Here is a picture of the Redgard.

    Bookmark   June 8, 2013 at 1:04PM
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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)

    Bookmark   June 8, 2013 at 3:27PM
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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.

    Bookmark   June 8, 2013 at 8:21PM
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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.

    Bookmark   June 8, 2013 at 9:24PM
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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.

    Bookmark   June 9, 2013 at 12:16PM
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