Bought Composite Shower Base - Are Their Instructions Safe?

[loddie]

Hi, I'm renovating my bathroom and as part of a tub-to-shower conversion I have bought a composite stone shower base. Because it is reversible for left or right drain, it has no integrated tile flange and instead comes with a plastic flange which is screwed and siliconed in place.

My question is this - after reading the installation instructions and watching the manufacturer's installation video (linked below), I'm confused about how the tile flange is placed against, rather than below the concrete backer board. Almost every other similar shower base product I've looked into shows the tile flange placed against the studs and then the backer board comes down to just above the flange. It is my understanding that tile/grout/thinset are not waterproof, so in my mind, water that has penetrated through the grout and thinset would hit the Redgard, run down the wall and have a path to my floor. Is this accurate? Am I overestimating how much penetration there is on a vertical shower wall? I have drawn out and attached a diagram based on the installation instructions that hopefully clarifies my question.

Installation Manual: images.thdstatic.com/catalog/pdfImages/c3/c3aa4e8c-f0bf-4700-bdf8-eff15e4b1069.pdf

Installation Video: youtube.com/watch?v=Nz_plAeJFxg

You'll have to copy/paste the links since the forum doesn't allow new user to include links in posts.

[Tool Guy - Kg]

Welcome to the forum, Matt!

Before anything, let me ask how big your rough opening and how big your shower pan is.

[loddie]

Pan is 60" (plus the flanges on either side at 3/16 each) and rough opening is 60.5". If the backerboard does indeed go in first, that'd necessitate cutting the base to fit, which is allowed per the manual/video, but not something I take lightly.

[John Bridge]

Hi Matt,

I've never run into a situation where the backer board goes behind the receptor, and I certainly wouldn't do it. Maybe you can steer us onto exactly which receptor you bought, give us a link.

[loddie]

Its this model by "Castico": homedepot.com/p/CASTICO-60-in-L-x-32-in-W-x-1-125-in-H-Alcove-Composite-Shower-Pan-Base-with-Right-or-Left-Drain-in-Black-Onyx-Slate-1B2S-3260SEBO/320024547

It seems to be a fairly new release as there are no reviews out there and the installation video they posted to Youtube was posted just 2 months ago. In researching similar composite shower bases, I did find that the Randolph Morris shower bases show a similar flange-against-the-cement installation in their instructions, here's a link to PDF of one:

vintagetub.com/download/Install/shower-pan-install.pdf

And for the sake of comparison, a similar model from "Wet Style" showing the flange installed against the studs instead:

secure.img1-ag.wfcdn.com/dm/document/d24a6e02-8dac-4519-9bfe-5971131ff813/wety1092_2_installation%20&%20assembly_1.pdf

Again, sorry that all the links need to be copy/pasted, as a new member the forum blocks me from posting links to fight spam.

[John Bridge]

The shower base would go in first and the backer board brought down to it. My problem is how to make everything waterproof without getting a mess around the edge of the shower floor.

If you bought the floor at the regular price you can return it, and that is my advice. Then you can start over with a tried and true shower system.