Designing Kitchens and Bathrooms - Tiling a Crack

I hate to ask a redundant question, but I've been reading posts for 30 minutes and can't find a clear answer. We are tiling our kitchen and have a reasonable sized crack running across the floor. I've read that ditra is the way to take care of this, but since we've already laid a number of tiles (a few a night for several nights) it's a little late for that since it's too thick. Is there another thinner product that does the same thing without throwing our thinset levels off? What about the roll-on/spread on/spray on stuff? I was looking at a product called Red Gard. Will this get the job done? Just spread it in and around the crack and thinset and tile over it? Don't assume I know anything because I don't. I can use all the help I can get. Thanks for any help you can provide.

I don't want to rain on your parade, but you did lay down cbu (concrete backer unerlayment) prior to beginning the laying of the tile, right? Where is the crack running from/to. Is is a normal seam? Are you laying it on concrete? Can you post a couple of pix on a site such as photobucket.com and give us the url?

madman - hey I like that name.

Give us a better description of the crack. How long is it, how wide is it? Is one side of the crack higher than the other (raised up). How old is the slab? Is there any other cracking?

I know you think its too late but ditra or some other isolation membrane is a good idea for any slab.

We are tiling on concrete.

The slab is 21 years old. There are no other cracks and given the age of the slab, it seems reasonable to not expect any more. The crack is level from one side to the other (neither side is higher) and is essentially not measurable as to how far apart it is. It's about 6 feet long most of which is under our refrigerator which is why we didn't see it before.

I can do pics later tonight, but not at this point in time.

We are 30+ tiles into this and I'm not seeing how we can just go back rip those up and lay down an isolation membrane and it not be an out-of-control amount of work. My hope is to cover over just the crack and move on.

Does this help explain?

Sounds like a hairline crack. If the slab is that old hopefully not much more movement. I like to use noble cis for this. Its thinner (1/16") than ditra and does the job. It may still be to thick for your situation though. Youll know that better than me. You could probably get away with using redgard as well. For either of these, you need to cover the slab with the membrane at least a full tile to the left and right of the tile that spans the crack (essentially 3 tiles). Which ever you decide, read the instructions before you use it. If you have other questions after that let us know. Good luck madman.:)

That's why I asked if it was concrete. Being a carpenter, my brain immediately went to a subfloor without cbu. HJ has you on the right track.

More questions for followup. Should I have a preference regarding a liquid like redgard vs. some kind of sheet that I lay over top? Is one better than the other? Is the answer go with both? Thanks for your help. You guys are awesome.

If you can afford the height, the sheet membrane would be better. One or the other, not both.:)