yet another question about vapor barriers

itsallaboutthefoodDecember 2, 2011

My contractor is using hardibacker 500 and was not going to use any kind of vapor barrier. I talked to him about putting poly behind the hardibacker or kerdi or other waterproofing on top. He prefers to tile directly on the hardibacker, so we decided on poly. However, he had some questions I could not answer:

1) Is it okay to have sheetrock, poly, hardibacker and then then thinset and tile?

2) Will putting poly behind the hardibacker negate the hardibacker guarantee since their installation instructions do not specify any kind of vapor barrier.

3) Can he use Tyvek or 15lb felt instead of poly?

4) What is poly? What exactly do you buy from Home Depot when everyone is talking about "poly"?

Thanks

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Avanti Tile & Stone

1) Seems that this would bump out the shower beyond the rest of the wall. Ditch the sheetrock, staple the barrier to the studs and then add the Hardi & tile.
2) No...without a vapor barrier, moisture can migrate to the studs causing mold.
3) 15lb felt is also fine. Build it from the bottom up, overlapping the seams.
4) Plastic sheeting, sold in rolls. Use 6mil, if they have it. Thicker is OK as well.

    Bookmark   December 3, 2011 at 11:44AM
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itsallaboutthefood

Thank you!

This is an existing bath/shower enclosure. The sheetrock is already there. The old walls had tile with like an inch of mud underneath. Our GC is putting the hardibacker over the sheet rock to bring the depth back up for thinset and tile which will have a similar profile as the old tile in that there are 1/2" bead trim pieces for the edges...it will not bump the shower beyond the rest of the wall at all.

Given this, is it okay to have the following...

sheetrock
15lb felt
hardibacker 500
thinset and tile

Thanks again!

    Bookmark   December 3, 2011 at 11:59AM
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itsallaboutthefood

When I say "bead trim pieces"...these are like 1/2" x 6" quarter round pieces to go with our 6"x6" tiles.

    Bookmark   December 3, 2011 at 12:01PM
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Avanti Tile & Stone

While I've always managed to not go over drywall with a vapor barrier sandwiched between it and Hardi, I don't see any reason why that shouldn't work. If it were my job, I'd simply Kerdi or Hydroban the drywall and tile on that.

You didn't mention if this is a shower or a tub "wrap."

    Bookmark   December 3, 2011 at 2:50PM
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itsallaboutthefood

This is a tub installed in an alcove with a shower.

    Bookmark   December 3, 2011 at 3:58PM
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Avanti Tile & Stone

OK...if the Hardi is up with no vapor barrier behind it, coat the face with two coats of Redgard from Home Depot.

Use pure silicone to seal the edges to the tub.

    Bookmark   December 4, 2011 at 12:53AM
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itsallaboutthefood

Actually, the Hardi is not up yet. And actually, the sheetrock is down too on part of the wall. The contractor is not keen about using something like Redgard (he feels it makes it difficult to tile over).

That is why I am asking him to put the felt between the sheetrock and hardibacker.

    Bookmark   December 4, 2011 at 10:42AM
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Avanti Tile & Stone

Shouldn't make any difference if he's using a good quality latex-modified morter...and I like not having the Hardi ever even get wet, as it can be with a vapor barrier behind it, however, be that as it may, tarpaper or a plastic poly liner behind the Hardi is perfectly acceptable also. Just "dealer's choice" here........

    Bookmark   December 4, 2011 at 12:24PM
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itsallaboutthefood

Thank you!

    Bookmark   December 4, 2011 at 12:57PM
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