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Unread 01-22-2021, 01:15 PM   #1
Shail
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SOS! help with Redgard and Cement board please

Hello,

I am a homeowner and do not have much knowledge. I am renovating my master bath. I insisted my contractor to use cement backerboard and redgard over it for shower walls. He was reluctant at first but agreed. He wanted to do it his way, which was no cement board or even if cement board, no redgard because he thinks the cement board is waterproof. I have had several leakages from upstairs master bath and we have been doing band aids for a long time before deciding to renovate. As imagined, the wood, floor all was rotten. He did a good job putting in new floor, laying cement on top of it.

But here is the problem, he wants to do things his way and apparently is not familiar with the use of redgard. I want to take every precaution to not cause another leak now. I sent him several links, manufacturer instructions on use of redgard, coating thickness, several videos. He is unhappy I am asking him to do this and yesterday he applied first coat of redgard (and I think it is not thick enough) that extended on the drywall above cement board all the way to the ceiling. When I noticed, I told him it is not to be used on drywall. Now he is saying why I did not tell him earlier. I thought he should know better. FYI - I am tiling all the way up to the ceiling. But since cement backerboard ends few inches above shower head, I think the redgard should also end there.

Questions:
1. Should he have hung cement board too all the way up to the ceiling?
2. Now that cement board ends many inches short of ceiling, should he not have applied Redgard all the way up?
3. Will there be any other vapor barrier behind the drywall portion as my tiles will go all the way up? I asked him not to put in plastic sheet behind cement board to avoid creating vapor sandwich.
4. What should he do now for the already applied Redgard over drywall part?
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Unread 01-22-2021, 02:04 PM   #2
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Welcome, Shail.

Let's start with the bottom. How did your tile contractor build the shower receptor? That's the waterproof basin at the bottom of the shower, sometimes referred to as the shower pan.

Photos would be very helpful here.

1. Not necessarily. The CBU is required in the wet area of the shower, but that technically ends just above the pipe for the shower head. Drywall above that is fine.

2. While Custom does not (I don't think) list gypsum drywall as a suitable backing material for RedGard, from my personal experience I don't think it will do any harm in your application. See my warranty information below.

3. If he had properly installed a moisture barrier behind the CBU such that it draped over the receptor liner (presuming a traditional shower construction), there would be no need for the RedGard. But you were correct to eliminate the moisture barrier if you planned to use the direct bonded waterproofing membrane (your RedGard) on the inside face of the walls.

The small area above the shower head is not likely to suffer significantly from having both a moisture barrier and a waterproof membrane, but you're correct again that you should not do both as a rule.

4. I would be inclined to let him complete the tiling as is. While it may not be technically correct, it sounds like your most viable option given the obvious problem of an uninformed contractor.

Biggest question is how was the receptor built.

My opinion; worth price charged.
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Unread 01-22-2021, 02:51 PM   #3
Shail
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Added some pictures. For receptor, he says he used mortar and plastic sheet. I couldn’t be present when he did the shower pan. So just taking his word for it as I am kind of loosing my trust in him. It’s too late to make any drastic changes now though in the middle of the project when the budget has already gone above initial estimate. I was having thoughts of ending the contract with him and finding someone else.
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Unread 01-22-2021, 05:13 PM   #4
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You're right, the Redgard is too thin. It needs to be credit card thickness.
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Unread 01-22-2021, 07:04 PM   #5
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Quote:
Originally Posted by Shail
For receptor, he says he used mortar and plastic sheet.
I'm more than a bit concerned about that, Shail. And I really can't tell much about what you've got from the photos.

I can't tell what the blue is around the edge. Looks like blue masking tape, but I can't figure why it would be there.

And I can't tell if you have curbs on those two open sides. Looks like there is some form there, but doesn't seem to tie into the walls at all.

Have you any photos from a little earlier in the construction? Or perhaps you can tell us what we're looking at there.

My opinion; worth price charged.
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Unread 01-22-2021, 10:04 PM   #6
Shail
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Yes that is masking tape. He has covered the shower pan with a cardboard and taped probably to protect from dust and debris. It’s a dual threshold dreamline slimline acrylic shower pan. The flanges are secured to the studs behind the backer board with screws.

Tried taking some close up pictures if this helps.

Now that it looks the redgard coat is too thin, how difficult will it be for an inexperienced person like me to apply one or two additional coats such that the wall is ready for tiling when he returns in 2 days? This is only first coat by the way. But I still feel it’s too thin.
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Last edited by Shail; 01-23-2021 at 08:48 AM.
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Unread 01-22-2021, 10:07 PM   #7
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Here are the additional pictures
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Unread 01-23-2021, 09:37 AM   #8
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Shail, the problem with your adding more RedGard to the walls is that once you do that, or anything else in regards to that shower, any subsequent problem or failure with the installation, will be your fault.

You can certainly add the RedGard if you want, but getting the required thickness is not as simple as painting the bedroom wall. Custom unfortunately no longer publishes the required thickness for each coat, but their requirement for coverage of 110 square feet per gallon per coat should be close to their previous requirement of a minimum of 20 wet mils. It's a lot more material than you'd normally apply when painting.

Should require the better part of two gallons to do those two walls.

My opinion; worth price charged.
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Unread 01-23-2021, 10:59 AM   #9
Shail
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The chart on the bucket says 1 gallon covers 55 sq ft if used as waterproofing membrane. That must be fir two coats then because their website says 110 sq ft per gallon each coat. My area till ceiling is just about that size 56 sq ft. or slightly more than that. And I am anyway not applying any additional coats on the drywall part of few inches above the backer board. So I think 1 bucket should be sufficient. I will just need two additional coats now because of the first being so thin.

Thank you for your professional advice here.
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Last edited by Shail; 01-23-2021 at 11:22 AM.
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