Tile Project Prep - Subfloor Issues

[eafd1996]

I am about to start a new tile project that involves taking over part of my garage and first floor which are situated on a concrete slab.

I need to make up about an 1 1/2" difference between where one room ends and this 10'x10' area begins.
I orginally had someone come in and float in concrete to bring the subfloor of the two areas to the same height. My wife orginally wanted to install tile in the two areas, but then decided to make one area wood and one area(the new area) tile. So now I have this subfloor height issue I have to deal with before installing the floor tile. I can't possibly make up the different all in thinset, but some advice on making up the difference would be appreciated.

I was thinking about just setting in a layer of Durock to make up some height but then after reading here and the Durock website I realized that was not acceptable.

Here are the facts:
Area 10'x10'
The tile are 17"x17" porcelain tile.
The subfloor (new concrete) area has some minor cracking issues.

My plan of action:
1. Redguard or install some anti-cracking membrane(recommendations?) over all or just the cracking areas of the present concrete.
2. Deck mud the difference in height(with a slurry of thinset on the base of the existing slab) using the advice posted on this website.
3. Install Ditra
4. Install tile.

Like I said any recommendations would be greatly appreciated.

[bbcamp]

Your plan is fine, except you don't need or want the Redgard. Bond the mud to the slab with thinset, then use a membrane on top of the mud. This presumes that the cracks do not have any vertical displacement. Ditra would not be the best choice for a membrane if the cracks are wider than 1/8". Use a membrane that is rated as an antifracture membrane, such as Noble's CIS. You will need to map out where the cracks are so you can install soft joints over them.

[eafd1996]

Thanks but what do you mean by soft joint? Is that where I install the anti-fracture membrane?

About the the Noble CIS installation...I guess you can install it with modified thinset? The primer and adhesive they sell seem like a lot of money.

[bbcamp]

Soft joint is a grout line with a urethane sealant in it instead of grout. It allows the tiles to move a little if the slab does.

Noble has a pretty good idea how much their products are worth. However, while any modified thinset conforming to ANSI A118.4 is acceptable, don't cheap out or else you could be wasting your time and money.

[eafd1996]

Last one...hopefully.

How much height should I leave for the installation of 17"x17" tile and the Noble CIS membrane(thinset joints included). I was thinking about using a 1/2"x1/2"x1/2" trowel for the tile.

That should leave me with the correct deck mud depth.

[bbcamp]

CIS is about 1/16" thick. A 1/2 x 1/2 square notch trowel will leave about 1/4" of thinset after you beat in the tile. Your tile should be about 3/8" thick, but verify that.