FH # 141, September 2001 had an informative item on installation of PVC membranes for custom ceramic shower floors.
One item not addressed in the piece, (or in the books at the local library) is how to address the short (2 – 3 inch) vertical surface between the threshhold and the floor.
Ceramic tile would seem out of the question because installation of a cement backer board would require screwing the cement board to the threshhold 2 X 4 too near the floor. Making a one piece cement board in the shape of a U to go up the wall an either side of the door and below the threshhold would create a weak location below the threshhold that could not be brought firmly against the vertical surface invity cracks in the ceramic/backer board from use.
So what do the pro’s do with the vertical surface between the threshhold and the floor?
Anwalt
Replies
Go to the Schluter site http://www.Schluter.com and follow links (products, waterproofing, shower systems) and look for the Kerdi shower video, showing installation.
Do not download the .mpg or .wmv file. It is not the installation video. For high speed internet, do the flash video.
You will see everything you want to see about waterproofing a shower, pan, and curb.
After that, to to the John Bridge forum site, and read all the stuff there about shower membrane installations.
Edited 4/4/2006 10:26 am ET by Gene_Davis
I'm still trying to figure out how unmodified thinset (or any thinset) is a waterproof bonding agent for anything. Since there are so many folks smitten with this system, I assume it must work, but I sure wish I could see it done first. No chance of that here. Today I submitted a proposal to do two Kerdi showers, so maybe I'll be getting my feet wet soon enough.
Do what Schluter's guy did. It is a test, and one of their techs up at the NA HQ did it.
Build a little cube box with an open top out of OSB scraps, maybe a foot to the side. Using Kerdi and thinset, line it. Let things cure for a day.
Then fill it with water, and just let it sit there. Add water as required to make up for evaporation loss as time goes by.
Tell us how many years go by without seeing a leak. We are going on 6 here.
That's an impressive test. When I looked at the construction details, I thought that it wouldn't leak, but it probably wouldn't hold water if it was filled up past a seam. Sounds like it'll hold water just fine. 6 years is a long time, I didn't realize the stuff had been in use that long.
zak
I'm still trying to figure out how unmodified thinset (or any thinset) is a waterproof bonding agent for anything.
It's not. The membrane is.
DG/Builder
If the membrane is seamed, and unmodified thinset is used to fill the seam, then the thinset is the bonding agent and I would think it would have to be waterproof.
Ok David, I see your point. The answer is not real obvious, but here is how this works.
The mortar is permeable. However, the mortar is thin and sandwiched between 2 layers of membrane. Note that the mortar is not in contact with a porous or absorbent underlayment. Absent significant hydrostatic pressure, there is nothing to force the water to leave the mortar and flow into the "seam". It will saturate and that's it. If there IS significant hydrostatic pressure, it WILL leak, which is why the following on their instructions:
"When anticipating large quantities of water, an impervious adhesive, such as a waterproof mortar, an epoxy mortar, or urethane may be used"
In a conventional mortar-over-cement board situation, the cement is very absorbent and will "suck" the water from the mortar. The cement will likely be wet. But note that if you have the cement installed over tar paper or plastic with an overlap "seam", water will not flow through that seam to the studs. The physics of the situation are similar.
DG/Builder
hey buddy...last week i built a shower curb and i formed the base of the shower stall at 5 1/2 " high and at the threshold 3 1/2" inches high using 2x6 and 2x4 lumber as the forms. Then i poured a 'monolithic" curb and now King Kong can stand on the curb...and also heaven forbid the shower pan membrane leaks...it can't rot away any wood because ta-daa there is no wood and if anything the moisture makes the concrete stronger (it is a basement shower...hard to screw up) ....also i bolted the bottom plates to the top of the curb that makes up the outline of the walls of the shower stall...the wood framing members are 5 1/2 inches away from the shower floor....also i sloped (slightly) the formwork so that any water sitting on the sills of the curb would be coaxed into the shower pan. It's easy enough you can probably just brace your forms to your subfloor....it's fun and when it dries you will be awestruck with the strength of it.
Didn't they have a membrane shower on Fear Factor once? Nasty...