I ordered the Schluter Ditra underlayment through ebay and it seemed to take a long time to arrive. But it finally did and I cut it to fit the guest bathroom and mortared it down. The Ditra might be super expensive but the unmodified mortar that it requires is the cheapest that can be bought, it was only about $7 for 50 lbs. The type of mortar is called thinset but the actual way to tell if it is the right type is if it meets the ANSI standard 118.1. I read this on the Schluter website and in the Ditra installation handbook and the description of the mortar at Home Depot includes the standard. Modified thinset is standard 118.3 or 118.4.
The Ditra is made from a stiff thin plastic grid that is backed by what they call fleece but reminds me of interfacing material.
It cut easily with a box knife. I would have used scissors if I could find them quickly but the box knife was closer to hand. The mortar is mixed by adding the dry powder to water. I used a 5 gallon bucket that I had to clean dried paint from first. After filling the bucket about a third, I added mortar until the mixture was fluid but held a notch. Fortunately I have all the tools for this job. I tiled quite a bit in Arizona and have a 1/2 inch electric drill that can easily mix concrete with a spiral metal mixer attachment and the 1/4 inch v notch trowel for laying the Ditra and a 3/8″ square notch trowel for laying the tile. So these were tools I didn’t have to purchase again.
I let the mortar sit 10 minutes and then spread a generous amount on the bathroom floor and pressed the Ditra into it with a small steel roller that I also already have on hand.
I had enough mortar left over to begin laying the full tiles on the diagonal pattern. I both spread the mortar on the Ditra and back buttered each tile as recommended in the Ditra installation instructions.
The next day I cut the rest of the tiles to fit and laid them out. It took all my work time to just cut the tiles, so it took another day to get them laid. The mortar mix was a bit less stiff this time. I like it a bit stiffer but this worked. It is supposed to be wet but firm enough to take a notch and this was.
Then it took about two hours to lay the odd shaped tiles in place. It took a little longer because where I was sloppy at the edge of the tile with mortar, I had to chip it out to lay the tiles next to the ones that were already installed. I chipped it with the box knife and vacuumed the edges before applying more mortar. Otherwise the mortar kept the new tile from laying flat against the mortared tile. I was more careful not to leave mortar at the edges for the rest of the install. I ran out of mortar towards the end and had to mix a little more.
Since I completely used one bag of mortar and needed more to do the job, I decided to wait to lay the door trim pieces. I have epoxy grout for the tile so I will have to learn to mix that accurately and apply it before we can reinstall the toilet.
I may need to ramp the tile a bit at the door and at the shower to minimize the change in levels. I left out the tiles nearest to the shower and I didn’t mortar the Ditra at the shower edge so I can place a waterproofing layer at the transition. I will have to figure out the shower tile later.