Tiles set into bitumen

[AMtek]

I recently repaired a small section of a macdonalds restaurant floor and now they have asked me to look at the floor in the kitchen section. terazzo tiles are set into what looks like bitumen, grouted with cement based grout, there are expansion joints dividing the floor into roughly 7m2 sections, the substrate is ply but i have no idea how thick, how it was fixed, if it was primed or what it is laid onto. The problems are that the oil from the fryers etc seem to be eating the grout away and working its way between the tile and bitumen and the tiles are debonding in big sections, the biggest problem however seems to be that the expansion joints fitted aren't coping and the rubber is being squashed out by up to 3mm and the whole expansion joint along with the row of tiles either side are being forced upwards forming a big ridge. I have advised that the whole floor needs scrapped and redone but not suprisingly they say that this is out of the question. I could re-lay the floor in sections on night shifts but if the substrate is no good i will be on a hiding to nothing. any ideas guys?

 

[turnip]

we always put a 3-4mm grout joint between the tiles and the expansion piece, is the current installation done like this? or the movement joint piece could be over a ply joint, maybe the plyboards were close butted and have heaved together over time (oil/moisture absorption), this might also explain the tenting, seems like a lot of stress on this floor anyway. I was mulling over mcd's at westminster cathedral, the floor there seems to be epoxy black grout in the kitchen area with 150x150 dorsets, big fat joints.
anyway, remedial works: larger grout joints, smaller tiles, joint against the movent piece, if the existing plyboards cant be removed and are close butted, get a 3-4mm joint cut into where they meet to allow for future expansion. best I can come up with.......