| There are a *LOT* of jack-leg hacks in the construction/remodeling
| trades. When you have your floors redone, make sure they use
| Schluter-DITRA uncoupling membrane.
|
| http://www.schluter.com/6_1_ditra.aspx

I happen to be going to a job this week where that
method was used. 6 months ago. Grout is cracking
and at least one tile is loose. I don't know whether
the job was done right, but I find it hard to believe
there's any good reason to float a tile floor on a
sheet of plastic when it can be done with time-
tested thinset on concrete board.

In this case he thinks the subfloor is concrete.
So what are you recommending? That he should maybe
fill in the loose gaps with sand mix, then float a
plastic-sheet-job and raise the whole floor by 1/2"
to 3/4"? That doesn't sound like a plan to me.

There may be hacks in the construction trade,
but it doesn't help that new, untested, "high
tech" replacement methods keep being cooked
up to replace doing things the right way.