There's no reason why a modified can't be used. Schluter only recommends unmodified because it's not necessary for high bond strengths or flexibility to bond Ditra to a concrete surface.

If you're going to use Mapei,I would just use a modified like Ultraflex 2. I have yet to see any supplier who stocks Ultraflex 3.

So the difference between the 2 is modified is for high bond strengths? I can get Ultraflex3 from my supplier no problem, as they supplied it to me the last time. If that's the case then I'm just going to purchase Ultraflex3 and use that to bond the Ditra to the floor and to bond the tile to the Ditra I'll use either Ultraflex 1 or 2. That should be ok right?

Paul

Modified is ok for the Ditra install but Ultraflex is a no-no for the tile over Ditra. You need an unmodified like Mapei Kerabond for the tile.

Just a note: Watch your coverage when using an unmodified mix with a porcelain tile. Make sure you have full coverage.

In some commercial applications with porcelain tile, spec will specifically call for a modified mix because of bonding concerns with the porcelain. That's mostly because some heavy floor cleaning equipment has been known to shake the tiles loose when laid with unmodified thin-set. I'm sure this won't be the case with the floors in your shop, but keep an eye on the coverage just to be safe.

When you say "heavy floor cleaning equipmenting" are you talking about buffers/waxers or cleaning chemicals?

I don't have to use porcelain but I prefer to. Thanks for the Kerabond tip. It's my first time using Ditra and I look forward to using it.

Paul

Make sure you use the notch size recommended by Schluter, or you will end up with humps and bubbles. Ditra can be extremely frustrating if you put too much thinset under it when installing.
As others on this tread have told you, cured concrete is an ideal tile substrate and does not need Ditra unless you need to use an antifracture membrane such as on young concrete or infloor heating.

Where you have that 1/8" crack in your floor, paint on a 24" wide strip of antifracture membrane like redgard or hydroban, or Aquadefence.

I assume any tile supplier would carry this anitfracture membrane? How about a Home Depot, Lowes, Rona, etc..?

Paul

There are several ways to handle situations where tile may fracture due to concrete shifting seasonally. While vertical displacement is virtually impossible to deal with, slight lateral shifting can be dealt with by using slightly flexible thinsets like Custom building products Megalite. or antifracture membrane. There is a wide variety of antifracture membranes. I have recommended the paint on ones, because for your application you already know where the cracks are and only need to isolate those areas. The paint on antifracture is the lowest profile height wise. There are also others that are peel and stick and of course Ditra, but there are height issues with those.

Yes, the box stores usually have them.