Too late to switch to kerdi?

Discussion in 'Shower & Bathtub Forum & Blog' started by Luke_l, Jun 10, 2013.

  1. Luke_l

    Luke_l New Member

    Jun 10, 2013
    So I am finishing my basement, and decided to try something new. Every time I tackle something around the house, I like to challenge myself somewhat. In this project, it was my first tile shower. While browsing Home Depot, I saw the price of kerdi, and I saw the price of a PVC liner and said to myself "it can't be that hard"... 2 liners, many hours of frustration, and 2 failed leak tests later... I don't know what to do. Here's what I have:
    -nice pre slope mortar bed
    -installed flange for non-kerdi drain
    -enough cement board for all the shower walls
    -wooden curb

    At this point, can I finish off with the kerdi membrane? What I'm thinking is:
    -rip out the old membrane
    -install cement board right down to preslope
    -put down rest of mortar base up to the top of the drain flange (plugging weep holes which will be rendered unnecessary)
    -install kerdi membrane over floor, up the cement board a few feet, and over wooden curb

    Only concerns are:
    -can I make due with the currently installed drain?
    -do I need to fully install membrane over entire tiling area (since tile + cement board isn't "waterproof" and water could get behind cement board)?

    Is a better option for me to install a liquid membrane instead of the pvc one and then finish as per a pvc membrane?

  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Sep 2, 2004
    Retired Systems engineer for defense industry.
    New England
    Schluter makes a conversion take the top of the clamping drain off, then add KerdiFix and bolt the conversion piece to the existing drain, then you can install the Kerdi Membrane. You need to cover the wooden curb with some CBU before you can put Kerdi over it - it is not designed nor will it bond properly long-term to wood. The preslope must come up properly to mate with their conversion drain's flange. You really should use the Kerdi to at least the height of the showerhead. Because CBU will absorb LOTS of moisture from the thinset, use a wet sponge to both clean the dust off it, and to add some moisture so it does not suck the moisture out of the thinset. Otherwise, it is very hard to get the membrane to stick properly. The thinset mixing instructions often have a small range of water to add...when installing Kerdi, use the maximum they allow. It should be closer to mayonnaise verses peanut butter consistency, but should still hold a notch and not run. If you get at least a 2" overlap of seams, and bed it properly in the thinset, it is waterproof. I'm biased...I like having a membrane surface waterproofing system verses a liquid. For a first timer, I think it's too hard to ensure you get the proper thickness without pinholes when applying a liquid. Too thin, it doesn't work...too thick, it has problems, too.
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