FIRST SCHLUTER SHOWER KIT QUESTION
We are in the process of installing a Schluter Shower Kit. We have put 1/2 concrete board on the interior – with modified latex thin set under the concrete board on the floor.
We have installed the Kerdi shower base and rough in drain and Kerdi membrane on walls and base. We used KerdiSet (a non latex modified thin set) as the instructions say and have the bubbles out.
Here’s the question. The tile that goes on the shower base is porcelain 1 inch octagon. What I’ve seen of this unmodified thinset doesn’t impress me as being something that can hold these tile – yet they say in the directions that if you don’t use non latex modified thin set they won’t warranty it (whatever that means).
I have been a fan of modified latex thin set and have had success with it. I would like some experienced input on this so we can avoid a hard lesson. It seems like what we use under this tile on the base needs to be really tough since under it all is a dense starfoam basically.
Replies
basically they require un modified because of the amount of time it would take modified thin set to cure sandwiched between the tile and schluter system (approx 30 days). if modified thin set is used and grouted 24-36 hrs after the tile has been set, you will be locking in a considerable amount of moisture that will prevent the mortar from curing properly.
Thanks Mark
after posting this I read a good article Ditra-set Tile Adhesive Thin-set Mortar | Tile Your World that dealt with the questions I had and the reasons behind it - thanks for this additional info about set up time
one thing that had me nervous is how easy the non modified thinset cleans off bucket and tools while you can berely manage to clean the modified thinset off - also thinset on the surface next day doesn't seem that tough but it must be misleading
I'm going with the Kerdi Set
a couple more points...
Mark gave the main reason for Schluter's modified vs unmodified...that the latex additives in modified thinsets need access (so to speak) to free air to dry, whereas unmodified thinsets don't.
A couple of points...not trying to talk you in to or out of anything. Just a couple of points...
1) Schluter tends to be very conservative. Their modified versus unmodified is a blanket statement, tile size be damned. If you're using large format tile? Sure, the thinset that's 9" or 12" from the nearest grout joint might not have great access to free air. So unmodified might be the better choice. You're using 1" tile. Any latex modifiers will only be a maximum of 1/2" from the nearest grout joint. There will be no drying problems with an installation like yours.
2) There are other manufacturers who have no thinset restrictions with regards to using their sheet membranes. Are they negligent? Less caring?
3) Quality of unmodified thinset...there is a difference. Example, at the box stores, HD sells Custom brand thinset. Masterblend (I think that's the name), their unmodified, is a pretty lousy product. If you add a couple shovelfulls of portland to each bag? You get a much better product, and it's still unmodified. But other unmodifieds, like the Ditra and Kerdi Sets? Yes, they have better forumulations, meaning more portland cement in them, right out of the bag. So not all unmodifieds are the same.
My opinion? Large format tile on a floor? Without a doubt I'd heed Schluter's advice. You'd have a slower cure, and foot traffic soon after installation could cause bonds that are not fully cured to break or weaken. Walls can be a different story due to no foot traffic.
Lightly modified versus heavily modified? For standard or small mosaic tile? Personally, I've never had a negative issue with using a lightly modified thinset between Kerdi and tile. Back when Schluter's tech reps were actually knowledgeable folk, they'd agree. Lightly modified, even heavily modified, under 12" or smaller tile would not present a problem. Now that their tech reps for the most part work off a script? They follow the script. Not modified thinset.
I know it's not available in your case, but for others there is the option of usig a shower system other than Schluter, they are no where as restrictive as Schluter regarding thinset use with their membranes.
Anyhow...just a few points to ponder.
THANKS MONGO - one other question
I was wondering about the difference mosaic makes in the drying problem. I'm leaning toward using the latex modified thinset now on the floor of the shower and bathroom floor. I have had success with the modified on mosaic.
Also - I would appreciate if you would comment on this: I have always back buttered too - though I notice how much easier it looks to install without doing that I'm thinking that's extra insurance. What do you think about a thin skim coat on the back ?
Don't back butter mosaic tile; expecially the super small kind. If you do, you MUST do an exceptional job cleaning grout joints, and in the process you run the rist of distorting the tile pattern. This become even more of an issue if you install tiny mosaic tile. Keep in mind that your grout will complete the tile-to-substrate process; in other words, thinset below the tile is not the only thing holding tile in place.
However (I have not done this but see no reason why not) you could backbutter your tile and let the up-welling thinset serve as grout. It's possible that dried thinset is not quite as water resistent as true grout. Perhaps others in this forum can comment.
They key points: 1)good contact between tile, thinset and substrate 2) avoid distorting the tile pattern 3) keep grout joints clean
Mel dba
http://www.froscarpentry.com
I THINK YOU'RE RIGHT
I'm wondering
what is twixted your ears.
The overlap sequence with Kerdi membrane is a non-issue. 2" overlap with non-modified thinset period. lap it anyway you want and it will be warranteed. If you want to shingle lap it all in order to make yourself sleep better at night, then go for it.
As for your claim that Schluter does not keep abreast of thinset technology (wether American, Eurpopean, Asian, Martian, or whatever): give me a break. Care to back that claim up, Mel? There are different chemical and working properties between modified and un-modified thinset. There respectvie use is job specific. Claiming general superior performance of one over the other is like saying aluminum is far superior to steel. BTW, bubbles developing during the "curing" process is pure fantasy. We're talking about installing substrate surface waterproofing here, not baking bread. Bubbles are the result of poor trowel technique, not chemical reactions. You say you've done 2 Schluter jobs, but I wonder if you've ever successfully completed a proper surface waterproofing tile job in your life.
CALLED SCHLUTER
We got delayed again - there was a roof leak over our bathroom (not our roof BTW) and we spent yesterday shingling into the dark before snow today. But during the day I called Schluter's 800 number. They assured me the KerdiSet was the way to go. Research is too expensive for me so I'm going with the KerdiSet.
Mosaic seems to make it a different ballgame. We did 2 showers with mosaic tile on pre-formed "tile over" bases several years ago. We got these shower bases from somewhere in Florida from some ad in a magazine from some company. They were just a plastic form with some starfoam inside in the curb and about 300 each.
The directions said to set them in "bull". I called them up to see what "bull" was and they said plastic roof cement. Well what did we know so I got a 5 gallon can of plastic roof cement and we put it under. The next day or two it was still squishy. So we cleaned that up, put it back in the can. It wasn't as bad as you would think. Actually it released clean from the shower base and I think I've still got some of it left (hopefully a lifetime supply).
Then we set it in sackcrete sand mix and funneled it completely full through three 1 1/2 inch holes in the top of the curb.
We glued the mosaic tile on with an epoxy made for that sort of thing. The tile laid there all day without the epoxy setting up a bit. A friend of mine told me that some really tough epoxies take a long time to set. I was nervous about that but the next day it was really hard.
We've never had any trouble or leaks with either shower - one upstairs and one down.
I used the KerdiSet today with fiberglass tape filling and leveling the joints in the concrete board on the main bathroom floor and I'm kind of warming up to it. I glued a couple of the mosaic tile together and I'm going to test the bond tomorrow. Of couse I mixed it heaver for the floor leveling than placing the membrane and it gave me a different impression.
The Schluter technician also told me to "back butter" the tile. We plan to do that.
If you really want to warm up to Schluter products, then try Ditra-heat.