Ok, so to the temp fix we came up with, I say temporary because we just don't know how much it will help. Maybe too little, too late.
After removing all the actual broken tiles, we cleaned the areas as best we could and replaced them using the specified adhesive, Kerrabond T and isolastic two part adhesive, which does not require priming.
We then cut control joints every 5 courses, full width of the room, and added a cold joint in a colour match Silicon to lessen the impact of the joints visually.
In the areas where tiles were crunching underfoot but not broken, we opened up the joints in what we hoped was strategic points and flooded them with a very runny mix of Isolastic and Kerr bond T.
We had tried it the day before in the cloakroom and it appeared we had had some success with the idea.
How effective it will be long term is anybody's guess, but far short of a complete rip out we felt it was our best chance of giving the client some time to sort out what they want to do further down the line.
They're fully aware our efforts could be a waste of time, but it'll give them some breathing space.
It's also worth mentioning that the tiler said that expansion joints in this floor were not needed!
Another issue that we disagreed with.
Finished floor.
