Flooring Tile - Tile over Soft Concrete

Just had old tile removed from a condo unit. Underneath is wonderboard over soft conrete. Contractor says he cannot remove wonderboard without severely damaging the soft concrete, the repairs of which would be at my cost (of course!). Says wonderboard never should have been layed over the soft concrete. Says best bet is to lay new tile over existing wonderboard (which is heavily damaged from the tile removal process and has most of the old thinset still on it) and lay enough thinset/patching material over it to level it out. Do not know if I believe this or not -- I have never heard of "soft concrete" before (this is a 1970's era condo unit, middle floor). Any thoughts??

Thanks,

-- Randy

I would remove the wonderboard and fix the gyocrete with a self leveling cement compound, then tile over that. Maybe even use a crack isolation membrand like Ditra, to be "safe".