Installing Durock for Shower Wall

Discussion in 'Shower & Bathtub Forum & Blog' started by MikeG, Apr 4, 2005.

  1. MikeG

    MikeG New Member

    Messages:
    55
    Location:
    District of Columbia
    Hi everyone. I'm new to the forum and it seems there is a wealth of great information here.

    I'm currently working on a masterbath remodel and I'm ready to install the cement backer (Durock) for the shower walls. It is a corner shower. The interior wall will be insulated with r-11 unfaced insulation. The exterior wall has the same insulation. My question is should I put a vapor barrier up between the insulation on the exterior or interior walls? When I called USG they seemed a little vague stating that the vapor could cause mold build up if water got behind the Durock but it was common to install the vapor barrier.

    The Durock will go up about 6' from the shower floor. I'm using green board for the last 2' of the wall on both walls. I am not installing a vapor barrier behind the green board.

    Thanks for your advice,
    Mike
  2. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    As I understand construction, a vapor barrier should be on the inside walls, to protect the insulation from moisture. Another way this is often stated is that if you are using foil-faced insulation, the foil faces the heated space. For sure, a moisture barrier material is always recommended under backerboard in the shower walls. On exterior walls, they use "house-wrap" such as tyvek, which 'breathes': it keeps moisture from entering from outside, but it allows any moisture from the inside to breathe out.
  3. SeattleSoxFan

    SeattleSoxFan In the Trades

    Messages:
    36
    Definitely!

    The cement backer board is porous and, though unharmed by water, will not prevent it from passing through. Tiles and grout is also more porous than you might think, so you should always put something behind. I'd suggest using 15# tar paper and overlap the lip of the tub (if one exists) to assure proper drainage should moisture collect back there.

    You can use other types of waterproof membranes (check out tile stores/books for suggestions), but tar paper is generally the easiest and cheapest :) Some people like to "glue" the joints with roofing cement, but if you overlap the paper properly it's probably unnecessary.

    You might check out johnbridge.com -- a frequent suggestion from this site -- for more tile oriented questions/answers.

    Oh -- you might also want to make sure you use a good PVA primer on the greenboard. It is a good idea to not put a barrier behind it, especially in a bathroom (greenboard vs. "gray" board has virtually no difference on mold). The PVA will create a vapor barrier on the interior side of the drywall -- which is the best place to keep it! Just make sure you have a decent fan and your install should stay dry last a long time.

    Good luck!
  4. SeattleSoxFan

    SeattleSoxFan In the Trades

    Messages:
    36
    Sorry Jimbo!

    You posted as I was writing my own response!

    Just have a few points/additions:

    Outside moisture is best kept outside and inside moisture best kept inside and any moisture in the walls needs to be able to escape.

    The trend for smaller builders around Seattle (a very wet environment) is actually backing away from Tyvek wrap-types back to tar paper because it allows greater breatability, and less precise installation with regards to taping, penetrations, etc. The big-guys still use it for sure, and when used correctly tend to do ok -- though all the buildings here being torn up b/c of mold problems are less than 5 years old and are all house-wrapped.

    And for interior walls, because of the newer, tighter homes, the old way of putting up faced batts or unfaced with poly causes moisture to hit and collect on the back face of the drywall, which usually just soaks it up and eventually molds... thus the benefit of PVA primers -- it moves the vapor barrier to the inside of the room, so the drywall stays dry.

    But there are countless opinions on both those issues I'd guess -- but I would definitely NOT count on faced batts as a "good-enough" vapor barrier behind the backerboard.

    There are some tile-backers that don't require (and in fact it voids their warrantees) such as dens-shield, which have a fiberous core and a vapor barrier coating, though it's still a good measure to paint a coat of membrane atop them.

    Just my opinion!
  5. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,139
    Location:
    New England
    Where you have the insulation with a vapor barrier, take a razor and put some slices in it, then put some tar paper or plastic on the studs prior to installing the cbu. The goal is to keep moisture from the studs, and, if you messed with the insulation's barrier, add one back. This will prevent any moisture from being permanently trapped between the two layers. My unprofessional opinion.
  6. MikeG

    MikeG New Member

    Messages:
    55
    Location:
    District of Columbia
    Thanks for the response everyone. Here's my plan... I will put 15# felt behind the Durock and not the green board. I was planning on taking the Durock up about 6' from the shower lip and green board the rest.

    Just to clarify the insulation is not faced so there is no vapor barrior there.

    Mike
  7. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    SeattleSox: Thanks for your input. Sometimes we tend to forget that conditions vary from place to place. It is so dry here (San Diego) that mold problems almost always stem from a plumbing leak, not building conditions. Your info about mold under Tyvek and mold on the backside of drywall is very interesting, and puts a whole new perspective on home construction.

    Thanks,
    Jim
  8. johnfrwhipple

    johnfrwhipple Bathroom Design & Build - North Vancouver, B.C.

    Messages:
    4,412
    Location:
    North Vancouver, BC
    Installing Durock for Shower Wall - using cement board to avoid the vapour sandwich

    Post(s) deleted by John Whipple
    Last edited: Mar 18, 2014
  9. johnfrwhipple

    johnfrwhipple Bathroom Design & Build - North Vancouver, B.C.

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    Location:
    North Vancouver, BC
    Durock's new Shower System

    Post(s) deleted by John Whipple
    Last edited: Mar 18, 2014
  10. johnfrwhipple

    johnfrwhipple Bathroom Design & Build - North Vancouver, B.C.

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    Location:
    North Vancouver, BC
    Vapor barrier - take a razor and put some slices in it. - Worst Online Advice of 2005

    Post(s) deleted by John Whipple
    Last edited: Mar 18, 2014
  11. John Bridge

    John Bridge Mudmeister

    Messages:
    49
    Location:
    Houston, Texas
    I'll second Jim's advice. When you are adding a moisture/vapor barrier on an outside wall it's a good idea to "defeat" the barrier on the insulation if there is one. Having two such barriers could form a "moisture sandwich" with any moisture that might somehow enter having no way to evaporate back out. I think Mike said his insulation is un-faced, so the point is moot. :)
  12. johnfrwhipple

    johnfrwhipple Bathroom Design & Build - North Vancouver, B.C.

    Messages:
    4,412
    Location:
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    Post(s) deleted by John Whipple
    Last edited: Mar 18, 2014
  13. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,139
    Location:
    New England
    Code generally requires ONE vapor barrier in a wall...where it is placed somewhat depends on whether you are heating or cooling centric. Having two can create issues...it's safer to just disable one and be careful about the one you add. John likes to twist words, and discredit anyone that disagrees with him. Regardless, what you do not want is for the wall SYSTEM to trap moisture in it...it must be able to dry out (and ideally, limit the moisture that does get in there in the first place). One, barrier, properly installed does that. Two or more, and you have potential to trap moisture in between.
  14. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,139
    Location:
    New England
    City hall will tell you you need one vapor barrier. Two in the same wall is asking for problems. John will try to poke holes in anything related to John Bridge's website, it's just his way. Get another opinion. Just like Terry doesn't dominate his site and lets others aid, this is true of nearly any help site. John Whipple wants to be the only one to provide tiling info. That's not healthy.
  15. Terry

    Terry Administrator Staff Member

    Messages:
    15,125
    Location:
    Bothell, Washington
    Let me post some items here.
    For starters, let me say that I think John Bridge knows his stuff!

    Now I'm going through and finding quotes and links on the web.

    R702.4.3 – Water-resistant gypsum board not approved on ceiling above the shower or over vapor barrier.

    IRC 06
    R702.3.8
    "Water-resistant gypsum board shall not be installed over a vapor retarder in a shower or tub compartment."

    [​IMG]


    A page on barriers.
    http://www.tigermountaintile.com/2012/08/27/shower-waterproofing-and-vapor-barriers-part-2/



    http://www.ci.newark.ca.us/images/u...dingInspection/B-5-TubShowerInstallations.pdf
    Last edited: Nov 1, 2013
  16. johnfrwhipple

    johnfrwhipple Bathroom Design & Build - North Vancouver, B.C.

    Messages:
    4,412
    Location:
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    Post(s) deleted by John Whipple
    Last edited: Mar 18, 2014
  17. johnfrwhipple

    johnfrwhipple Bathroom Design & Build - North Vancouver, B.C.

    Messages:
    4,412
    Location:
    North Vancouver, BC
    Durock vs Wonderboard Lite

    Post(s) deleted by John Whipple
    Last edited: Mar 18, 2014
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