Mapei thinset and shower waterproofing
I am putting in a large shower in a basement. The motor shower pan with liner is already done. I am getting ready to hang to 1/2″ Durock, but when I went to pick up cement tape and thinset for the joints, I noticed a product by the Mapei company that used flexible mesh over the entire cement board application (not just the joints), and some kind of flexible water proofing mix that was “skimmed” over the entire meshed cement board surface.
I can only assume this is some sort of epoxy or polymer modified thinset that acts as an additional layer of water proofing.
Has anyone heard of this product? Is it just overkill for a shower application, and if so, should I stick with more familiar water based thinset and fiberglass typed seams?
Grout, thinset, mortar, and durock, are all wonderful things. But none of them is waterproof.
The liner in the pan is the waterproof layer for the base and the bottom few inches of the walls. But you need something that keeps water that hits the walls, from going through them.
Waterproofing for the walls can be done in a few ways. You can put 6-mil plastic behind the durock, and lap the bottom edge of the plastic over the front of the pan liner. You can do the same with builders felt. In either case, be very careful to not rip the barrier while covering it.
Or, you could use Schluter's Kerdi product. It's great stuff, and a lot easier to work with than you might think.
Also, there's a tile-specific forum that has tons of great information, over at http://www.johnbridge.com
I won't be laughing at the lies when I'm gone,
And I can't question how or when or why when I'm gone;
I can't live proud enough to die when I'm gone,
So I guess I'll have to do it while I'm here. (Phil Ochs)
Most every company has a topical waterproofing membrane. If you have a vapor barrier behind the cement board, you don't need another barrier on the cement board.
So with a vapor barrier behind your cement board, just use mesh tape and thinset on the cement board joints, and tile away.
If you don't have a vapor barrier behind the cement board, then go with one of the many topical membranes out there.
Personally, I prefer sheet membranes like Kerdi over roll-on or trowel-on membranes. The roll and trowel membranes often need mesh reinforcement, plus you need to be aware that there are mil thickness requirements to get the required level of protection that you need, and while applying the membranes, it's common to get entrapped air that can cause pinholes during the curing process. Not a big deal, but these things do need to be considered. Plus not all of the waterproofing barriers are necessarily vapor barriers.
Here's a Kerdi Shower I did a while ago. It'll fill you in on most things you need to know to use the product.
Thanks for the replies. Part of my confusion comes from the article in Taunton's book. I can't remember if it's Renovating a Bathroom or Tiling, but the article describes only using a vapor barrier if the author is doing a steam shower. Otherwise he hangs Durock directly on the studs (and lets the wall "breath", thus avoiding mold growth on tar paper.
This is in a basement, right? Basements are generally cool, and might have moisture levels above those in the main house due to the basement being below-grade.What I would not want is for warm moist air from the shower being driven into a wall assembly, where it could cool and condense.Elsewhere in the basement I'd use an insulation that is vapor permeable. But in the bathroom I'd want to contain the moisture within the bath and then use mechanical ventilation to move it where I want.My opinion.