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help please! waterproofing under acrylic base?

15 years ago

We are building a house and I've been lurking here for quite awhile. Suddenly there are some questions about our master bath walk-in shower. We bought an acrylic base b/c I didn't want to be cleaning grout in the floor. The plumbers installed it by screwing into the framing as per installation instructions. The instructions also called for a mortarbed under acrylic, which they cut corners on and only installed some thinset or something in a couple places underneath to make sure it felt solid.

Now the drywallers showed up and unbeknownst to us, put in some kind of backer board (looks like drywall but with a gray paint-like coating on it) in the shower. The tilers were supposed to be putting up the backer. Now that I'm trying to figure out what to do, the tile installer mentions that they like to put a bladder under the acrylic base that runs into the drain. ?! I never anticipated anything like that. I thought acrylic was impervious to leaking, so you just had to worry about that behind the tile. He basically agrees, but says there's nowhere for them to run their bladder into for any potential leak in the grout. Am I making sense? Can anyone help me figure out what I should really be doing at this point. any help will be greatly appreciated. Thanks!

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Comments (2)

MongoCT
15 years ago
I have to preface this by stating that I don't do acrylic bases. However...

An acrylic base does not need a membrane underneath it. What will kill an acrylic base is flexing; flexing in the tray can cause it to eventually crack, flexing around the drain can case a failure near the drain.

To prevent flexing, many manufacturer's recommend their bases be installed in a mortar bed. And as you discovered, mortar spots do not make a mortar bed.

Once the base is set in a mortar bed, normally 6-mil poly sheeting is run on the wall studs and the bottom edge of the poly goes over the flange in the acrylic base. This way any water that gets through the wall will hit the poly and not enter the framing bay.

Over the poly sheeting goes your cement backer. Either a true cement board like Wonderboard or Durock, a fibercement like Hardie, or a (cough cough, ugh) gypsum core product that has an acrylic skin on it like DenShield. If you use any type of lightweight gypsum core product, every nail or screw hole and sheet edge needs to be detailed correctly.

Then you tile over the backer board.

If you know the make and model of your acrylic base. read up ion the installation instructions. If it requires or recommends a mortar bed, then get one.

If you don't have any sort of membrane (poly or lapped tar paper) on the walls between your backer board and your framing, then the wall board needs to come down.

Yanking the acrylic base and the wallboard sounds like a huge step backwards, but it'll only cost you a few hours. But it's nothing like the horror you'll enjoy of having to demo and rebuild a leaking shower.

And for bedding the base in foam, I don't agree with that method. If it needs a bed, then mortar, not foam.

Mongo
heatherummel
Original Author
15 years ago
Mongo,
Thanks so much for answering. Somehow I missed it when you wrote.
Heather
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