If your simply have "dirty Ditra"...thin smears of thinset that have little-to-no thickness to them...then it's not a problem at all.

If your bits of cured thinset are buried in the recessed grids of the Ditra...that's not a problem.

If you have cured globs of thinset that make the Ditra "bumpy" when you run your hand over the surface, or that catch the edge of a trowel when you run the trowel across the surface of the Ditra? You want to remove those globs. Anything over 1/8" thick should be removed. Or knocked down so they protrude less.

You should be able to knock them off with the edge of your trowel.

Prior to tiling, you'll want the surface of the Ditra to be relatively smooth. That way there will be nothing to interfere with your tiling. Any cured clumps of thinset over 1/8" thick that make the surface significantly bumpy? They may cause your tiles to not sit as flat as they should.

A 1/4" gap between adjacent sheets isn't a horrible thing, but there's no need to pre-fill that gap with thinset prior to tiling.

When I tile over Ditra, I first use the flat edge of my trowel to fill all the cavities in the Ditra with thinset. Then I immediately apply more thinset over the Ditra, this time using the 1/4" notched side of the trowel to cover the Ditra with ridged thinset.

Then tile. As each tile is set in place, it'll compress the 1/4" tall ridges into a continuous 1/8" thick bed of thinset between the Ditra and the tile, ensuring full coverage and a proper bond.

If the back of your tile is a waffle structure, you can back butter the tile with a thin coating or thinset prior to setting each tile.

Set your first tile, then pop it off. See what the coverage looks like between the tile and Ditra. It good, your methods are correct. If not, adjust accordingly.

Good luck!

Thanks very much for your responses - I did install the tile

As the pictures below show, I am making progress, almost done. Except the last section for the air-condition/heat register. It got really late when I got there - and I couldn't disturb my numbers with my grinding tile cutter - so I had to abandon that last tile, and will finish it up this morning. Lesson learnt: get a small tile cutter - which could have helped finish up the job.

Second lesson: never depend on your cordless drill. They never really twerk (pun intended ) when you urgently need them to - i had to search vigilantly for my corded drill to finish the diamond cuts when the cordless kept stopping along the way.

So, my questions are:

(1) When should I apply the grout - this afternoon or tomorrow - around 11.59pm would be exactly 24 hours when I completed?

(2) Secondly, do I have remove the thinset between the tiles (where I put the spacers) before applying the grout - or just apply the grout over it?

(3). Finally, is it ok to have some slight (about 1/10 of an inch) difference in height between adjoining tiles? I checked the floor level before the install and it was indeed level. Is there anything I can do during grouting to even it out.

thanks and I appreciate your constant encouragement and support..

cheers - Oyiwaa

(1) When should I apply the grout - this afternoon or tomorrow - around 11.59pm would be exactly 24 hours when I completed?

I'd give it 48 hours before grouting. Your thinset and grout bags may have waiting times, but most people grout the next day. The reason I say 48 hours is that with Ditra, the thinset can take longer to cure.

(2) Secondly, do I have remove the thinset between the tiles (where I put the spacers) before applying the grout - or just apply the grout over it?

If it has oozed up high in some places, then yes, scrape it out. What you don;t want is deep grout in some areas and a thin veneer of grout over thinset in other areas. That can lead to shadowing and blotchy grout color.

(3). Finally, is it ok to have some slight (about 1/10 of an inch) difference in height between adjoining tiles? I checked the floor level before the install and it was indeed level. Is there anything I can do during grouting to even it out.

Lippage does happen. In commercial installations, the general guideline is for maximum lippage to be no more than about 1/4th the width fo the grout joint. So if you had 1/4" grout joints, 1/16" inch of lippage is allowable. That guideline is for professional installations.

If you have significant lippage in the corner of the room, it might not be an issue. If it's in the middle of a walkway where you think you might catch and rip a toenail, then it could be a problem.

When you grout, simply fill the grout line full-depth with grout. With full joints, the grout can sort of act as a "ramp" from one tile to the next. If you were to instead rake the grout out of the joint and create a slight recess either during installation or cleaning, then you can accentuate the lippage.