Thinsets for Schluter shower kit

[T-rev]

Hi - new poster and DIY. Sorry if these questions have been asked and answered before:

I'm installing a Schlulter shower ST & SC kit and want to make 100% sure that I'm planning the proper type of thinset for my project. I'm have concrete board on the walls and a plywood floor. I have read some conflicting guidance regarding modified and non-modified thinsets for use with Schluter Kerdi.

I will tile the floor with porcelain and the walls with ceramic. The tile for the shower tray I believe is a 2"X2" mosaic of ceramic?!

First of all, I have bought two different bags of thinset from the local Home Depot here in Western Canada; Brand names are "VERSABOND" (polymer-added) and "CUSTOMBLEND" (non-modified)

From what I understand from reading the notes on the Schluter website and instruction manuals, an unmodified thinset is recommended for used on both sides of the Kerdi. I have talked with a local contractor that claims he has installed dozens of these shower kits and uses a modified thinset exclusively. Another reference claims that a modified thinset is used between the concrete board & the Kerdi and unmodified must be used between the kerdi & the tile.

1) Does anybody know of these particular brands of thinset? I've searched through other postings and only see foreign names mentioned and don't know how they compare to what is available here.

2) Does Schluter support a modified thinset between the sub-surface wall (concrete board) and the Kerdi membrane or does it have to be an unmodified?

3) Will an unmodified thinset be strong enough bond between the shower tray and the mosaic tile?

For the walls I planned on doing exactly as Schluter recommends; unmodified thinset for the Shower Tray and Curb to floor...

Thanks in advance for any insight you can give.
Sincerely,
T-rev.

[Brian in San Diego]

T-rev,

Hello and welcome to the forum! Schluter is specific in what thinsets they want where in the application of their products. If HD is your only source for thinset then I think you are in trouble if you want to follow Schluter guidelines to the letter. Versabond is a slightly modified thinset and is a good product that is popular. I wouldn't use CustomBlend for anything...that's my opinion. Have you tried inquiring at tile shops or places where pros might buy their materials? Here are some good unmodified thinsets...Laticrete 317, Mapei Kerabond, Hydroment Ditraset and Laticrete Megabond (available at Lowes). There certainly are others, but those are a couple I am familiar with. I used Versabond to imbed my kerdi and it worked fine. I used Versabond to imbed Ditra to a concrete floor (a Schluter no-no) and it's fine.

If you haven't done so I think you should spend 10 bucks and download The Kerdi Shower Book by John Bridge...worth every penny. It'll answer many of your questions. I know what the Schluter instructions say but if I were putting down a kerdi tray over plywood or osb I would use Versabond.

Schluter says unmodified under and over kerdi.

An unmodified will have no trouble holding your tile.

It sounds like you are concerned about a warranty. If you change your mind on that you could definitely use Versabond to apply the kerdi and IMO you could set the tile with it also. It's up to you. I would use Versabond over CustomBlend warranty or no warranty.

Brian

[Rod In Georgia]

My supplier of Kerdi is recommending Laticrete 317 Floor and Wall thin set mortor. I just put up my first 2 panels yesterday and they look great this morning

[Lonnie Walker]

I am also looking to install the kerdi shower kit and talked to a Schulter rep about the thinset issues. I guess I can understand using unmodified under the kerdi, but I would think modified would be better over the kerdi, or under the tile. Schulter says the recommend unmodified because there can be issues with the modified not drying properly with the waterproof kerdi. That is all I got out of them. I will probably use the Laticrete 317.

[jadnashua]

The cement in the mortar will set without air - moisture actually enhances its strength. BUT, the modifiers need to dry. Without both actions, you never reach the design strength. Kerdi is essentially waterproof. Put a big tile on it and most of them are nearly impervious (especially some of the porcelain and all glass tile). So, it can take forever for it to fully set - literally weeks and weeks unless the tile sizes are very small allowing lots of edges. Most people rarely wait long enough to let it dry if they use a modified thinset, so things can fail. A DIY'er often works much slower than a pro would, and a lightly modified thinset can work, but a good unmodified will always work. The things that differentiate good ones from poor ones is the quantity of cement and the consistency and size of the sand...quality materials cost more as does the concrete.