Preferred Kerdi Shower Wall Material

[jadnashua]

Been said lots of time, but the real problem with modifiers are those that are required to dry to become stable...the cement will cure after being wetted, regardless, but the modifier is wrapped around the cement when it's mixed right, and can remain soft until it dries out. Latex modified mortars need to dry to become stable, and that just doesn't happen quickly between a modern porcelain tile and a waterproof membrane as that moisture needs to either permeate the nearly impervious membrane, or the tile, but more readily, through the grout joints that might be filled with an epoxy grout which, itself is fairly impermeable. It can take literally months.

Otherwise, if the modifier doesn't need to dry, it should work. Only the thinset manufacturer knows for sure. It's not the amount of modifier, it's how it plays out in the whole mix if it stays wet for a long time.

I put in a moisture sensitive stone tile over Kerdi in my shower with Versabond, and it took nearly two weeks for the color to change back, but they were well stuck! A good porcelain could easily take months to fully dry out all the way across the tile, and if it wasn't stable until that happened, it could be a big problem. Moisture content and stability may or may not be directly related depending on the modifier used.

[bcs001]

I appreciate the technical details on how modifiers cure and the use of impermeable materials used for waterproofing. This has me rethinking my choice of mortar under these large size tiles. I’ve been reading past threads about using non-modified thin/medium set adhesives and the lack of widespread industry acceptance on their use over Kerdi.

At this point, I’m just needing to make a choice for this project and if using the Schluter brand mortar is the safest option, I will that. Or, if there is an easier/better performing option, I’d like to find out about it and then make a decision this week while I gather up the rest of the tools and parts I’ll need to complete this project.

[bcs001]

I went ahead and ordered the 3/8 slant notch trowel for this project but was driving home the other day and the thought struck me that the concept of having the notches of adhesive fall over on the adjacent grooves on walls will require combing only horizontally and only with the notch slant leaning downward.

Is this a correct assumption and I’ll need to practice my left hand combing technique in parts of the shower?

[cx]

I've never actually tried one of those slant-notch trowels on a wall, Bruce, but I see no reason it wouldn't work in any orientation if your pookey is mixed correctly. You still want to trowel in one direction rather than in swirls, though.

Don't think the trowel cares which hand you use.

My opinion; worth price charged.

[bcs001]

I've spent some time here searching for an acceptable medium bed mortar to use over Kerdi that will cure/dry in 7-10 days before grout. After reading the potential concerns about really long dry times using a modified mortar like Mapei Ultraflex LFT, I am back to seek a little more advice before deciding.

I've looked for Mapei Kerabond and Ditraset but they are not available in my area. I can get Schluter All-Set from a tile big box store nearby and the Mapei Uncoupling Membrane medium bed. There's a big price difference between the two but on a shower project that's not much of a consideration.

I'll be working with a 3/8 slant notch trowel if that in anyway enters into the mortar suggestions.

[jadnashua]

The critical thing that needs to dry is a modifier that is not stable until that happens. Most sold today are stable while still wet. Some of the rapid set ones can be grouted in hours, and they certainly aren't dry by then. It's more critical on a floor where you may be walking or moving furniture than on a wall.

[cx]

Bruce, there are no "medium bed" mortars in the ceramic tile industry. The mortars that previously were called medium bed and now properly called Large & Heavy Tile (LHT) mortars.

I have not yet tried the Schluter All-Set mortar, but would recommend it rather than the MAPEI Uncoupling Membrane mortar.

My opinion; worth price charged.

[bcs001]

I wanted to finish this thread out by posting final results. Overall I was satisfied with the end result and using Kerdi did seem better/easier than the traditional dryset pan, CBU walls and redgard waterproofing I used in my previous projects.

Thanks for the advice along the way.

[Igman]

Congratulations, Bruce! Looks fantastic!