I'm trying to decide on insulation interior walls of a shower for acrylic surround, and had just read that hanging a polyethylene sheeting on top of the drywall (between surround & drywall) was recommended because if moisture penetrates the surround, it stops at the sheeting and does no damage. However, at least 2 people replying on another person's similar question stated no sheeting / vapor barrier should be used. Might you change your mind about this based on them indicating it to be on top of drywall instead of behind it? https://homeguides.sfgate.com/need-moisture-barrier-building-shower-enclosure-70644.html

1 Answer 1


The article was a bit sketchy on a few details, but remained consistent in saying you need a vapor barrier. Of course installation behind the drywall (or whatever backing is used) will offer no protection to that surface.

Though it is a bit pricy, I recommend a rolled on liquid barrier such as Redguard or Aqua Defense on the backing regardless what it is. It is actually good protection that will not tear, and provides an isolation membrane under tile, if that is you final surface.

Using this type of water/ vapor barrier has saved me repair costs when there were accidents, or abuse, or just plain years of use in my rental properties. I believe it is the way to go.

  • ty so very much for the quick reply, really appreciate insight shared. I'm not tiling, will be an acrylic surround instead - no grout to worry about failing as has happened w/ shower just demo'd; but I was thinking the same until I found this video where he did a test - a seemingly very methodical and thought out process even with measurements for mil coverage; and it ended up with water filled bubbles.., ;-/ youtu.be/z-5egEwIxzk he even has a video about kerdi systems failing. i'm at loss, was up till 3am trying to find best approach. silveRboard under drywall appears to be 1 option.
    – LA Fos
    Feb 2 at 15:12
  • I watched your video, and found some basic errors were done in application. A glaring error was filling the box with water. The product is not made to be the frontline defense for a tub of water. I saw a youtube video of a guy that coated a cardboard box with redguard, filled it with water and left it on his deck for 3 weeks with no leaks ! A real world simulation would be spraying it with some water, or filling and dumping it out after a few seconds. Your shower will not be filled with water overnight. The product routinely performs it's intended purpose.
    – RMDman
    Feb 2 at 15:32
  • A liquid product over the sheathing behind your acrylic surround will be the best protection you can get in the real world, and is looked at as overkill by many in the bath remodeling trade. Forget the pseudo science, techy ,spec heavy youtube vids and sleep well .
    – RMDman
    Feb 2 at 15:38
  • so glad you gave this insight on video! i want to insulate walls; if you will, are you comfortable sharing what specific products you would use? i work fulltime job as well, & being up till 3am cannot happen again - all to probably still not be confident in what I'm using.. so far i was looking at these: 1) rockwool unfaced stone wool batt 2) then silveRboard on top/across studs 3) then drywall - except i can't find green anywhere, purple is all i can find 3) waterproof product - redguard or is there a better one? **I’m getting old, can't keep doing this kind of labor with future issues. lol
    – LA Fos
    Feb 2 at 15:59
  • to be clear are you insulating interior walls for sound deadening?
    – RMDman
    Feb 2 at 16:06

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