Is it really a “double vapor barrier” when you waterproof the inside of a tub surround?
My question is in regards to the implications of applying a waterproofing membrane onto permabase which is installed on an exterior wall that already has insulation and a poly vapor barrier behind the permabase.
I am in the northeast climate, where we typically put a poly vapor barrier on the warm side of the wall. This is exactly what I did, then I hung permabase over that for my tub surround.
I also want to apply a liquid applied waterproofing membrane such as Redgard to the inside of the permabase, so that any moisture that can and will get through grout joints will not get into the permabase. I also will seal the permabase at the tub flange with 100% silicone caulking.
I am hearing that this could be a “moisture sandwich, essentially trapping any moisture that may enter the permabase as vapor.
Whoa. Is this overthinking the scenario, or is this backed up by hard evidence that this is a bad idea?
It was reccomended that I slice up the poly vapor barrier behind the permabase only and keep it in tact everywhere else if I do in fact want to install the liquid waterproofing on the inside face of the permabase. Logic here being that the liquid waterproofing is also my vapor barrier in those areas.
Please someone help me make sence of this. Slicing up the vapor barrier that I just installed and diligently taped and caulked just seems extreme to me. This can’t be the first time a tub or shower surround is also an exterior wall with a vapor barrier, so what is typically done when you want to waterproof the inside of the substrate as well?
Replies
Technically it's not good to have a double vb, but in your case I wouldn't take anything apart since the only thing between the two is cement board.
What I would do however, is not use redguard, but rather spend the extra money on a professional grade product from a tile installation supply store. Redguard has a bad reputation, even though it's rated for use a a membrane in shower enclosures. A professional grade product will cost two or three times what redguard does, but it's much more durable. I've noticed in some box stores that redguard has been replaced by other higher quality products.
Thanks for the good advice on the Redguard I am all for getting a better product even if it means shelling out a little more dough.
The extra cash pales in comparison to the effort going into this remodel so it doesn't make sense to skimp on something like that.
Any products that you would reccomend?
I've not heard any guff about Red Guard... the tile guy at JLC loves the stuff.
Most of the tile guys at jlc including the moderator don't use redguard for shower surrounds. They may use it as a crack isolation membrane, or even in less critical wet locations, but I've never heard of anyone there using it as a shower pan.
Off the top of my head I can't recall the more common products professionals use, but my tile supplier says the highest grade product they sold was laticrete hydroban at around $100/gal. It doesn't require fiberglass reinforcement in corners, bonds to pvc and is easy to use. Don't skimp on coverage and read the full installation instructions before setting your drain and for selecting a drain setup since it isn't the same as would be used with a sheet membrane.
http://www.laticrete.com/contractors/products/waterproofing.aspx
There are other products that can be used, but the installation instructions need to be read carefully - not all liquid membranes bond directly to the drain plastic and require specific configurations to meet the manufacturers specs at the most critical area - where the drain transitions and joins the membrane.
You can search the jlc site for more detailed recomendations, but a lot of guys use hydroban.
You'll see it repeated in various places, but don't skimp on the thickness - that's what gives it durability.
You'll enjoy using the stuff - it's easy to apply and easy to tile over.
The whole "double vapor
The whole "double vapor barrier" thing gets far too much play and is greatly misinterpreted. The real issue is having a vapor barrier on the "wrong" side of the insulation, whether single or double.