Thinset question

[SilverBullet07]

I am using CBP VersaBond To bond the ditra to plywood. Can I use the same to lay 6x12 marble to ditra? The ditra website says to use un-modified to lay tile to ditra. But I am reading on some posts that it can be used. So I’m a little confused.

I thought ditra to plywood ANSI 118.11
Tile to ditra ANSI 118.1

I am having trouble finding a white 118.1 cbp thinset to use and if I can use the Versabond they have it in white.

[HouseOfJoe]

You want modified for the ditra to plywood, that's Schluter's recommendation, so you're good with the Versabond there.

Schluter says they want unmodified for the tile to the ditra, but I've been told by a couple of the pros around here that Versabond was going to work just fine for my ditra heat application.

The reasoning I've heard from CX and others is that Schluter knows that some modified thinsets (Versabond among them) will work just fine with their products, but they don't want to be in a position to have to test each and every modified thinset out there, so they play it safe and say to use only unmodified thinset.

Mine has been down for a week now. I see no issues. But I've given it a week before I grout *just* to be sure. The issue is the thinset's ability to cure. Modified has to have air to do that, and it can't get air through the ditra, and probably can't get it through the tile (depending on what you have) so it has to get it from the perimeter of the tile.

[John Bridge]

VersaBond will work fine over Ditra.

[Kman]

If you want to speed the dry time a little, pre-fill all the cavities in Ditra the day before setting the tile.

You'll still need to skim the surface of the Ditra to burn in a layer mortar to the dried mortar on the mat, but with the mortar in the mat already dry, the dry time of the bond coat will be shorter.

[jadnashua]

The issue is, there are at least four different materials that can be used as modifiers for thinsets (and also vary in quantities), and manufacturers can and do change their configurations on occasion. Those that use latex as a modifier are problematic. Most do not need to dry to achieve stability and strength. Since Ditra is impervious and a modern porcelain is very close to it, any that needs to dry to become stable can take literally months to dry out. The cement cures at the same rate, whether is is damp or dry, but until the whole mix is stable, the crystals that cement grows can shatter, weakening its bond. Schluter does make a modified that they know will work. It's a liability and testing thing they do not want to deal with when they say to use an A118.1 mortar on top of Ditra. They know that WILL work, as well as their modified. You need a quality A118.1 product to work well. SOme of the price leader, cheap, ones are literally, mostly coarse sand with a little cement in the mix. A premium mix will have fine sand and more cement that will spread and flow better, and with the higher cement content, make a stronger bond.

[SilverBullet07]

Thanks everyone. I’ll use the Versabond since I already have it for the ditra.