Id be focused on the fact that you have movement rather than how to fix
the tile for now. Because next or eventually it will be the doorways
then the drywall, plumbing, ect.
I did this as instructed. The specific product I
used was called Pro-Red Waterproofing Membrane,
"elastomeric waterproofing & anti-fracture
membrane".
Sounds like the red membrane (looks like very thin red fabric set into
the coating while stil wet) is part of the system you left out or di I
not read it correct?

Robert A. Cibiras wrote:
I laid ceramic tile over a concrete slab - new
construction. There was a crack in the slab before
any tile was laid. I was told by a local tile guy,
to use a rubber membrane brushon coating to cover
the crack.

I did this as instructed. The specific product I
used was called Pro-Red Waterproofing Membrane,
"elastomeric waterproofing & anti-fracture
membrane". Part of the product description even
states, "reduces crack transmission in ceramic
tile or stone..."

Everything has been good for about 3 years. A
couple of months ago I noticed a cracked tile, and
put it on the "to do" list. Last week, it had
spread to include 3 tiles total. So I decide that
today is the day I will chisel the tiles out, coat
the crack with the membrane, and lay new tiles in
a day or two.

Imagine my surprise when I begin removing the
tiles and discover that they are some of the tiles
lying over the already coated crack.

So now I am essentially back to the beginning -
sort of. If the membrane didn't stop the tiles
from cracking the first time, what would make me
think a reapplication will be any different? Based
on this, can I expect the tiles along the other
25' of the defect in the slab to likewise crack
over time?

What can I use to prevent future cracks in the
secton of slab that is now exposed? What, if
anything, can I do to prevent other tiles that are
currently laying on the slab, over the membrane
coated fault line, from cracking?

Thanks for any help.