hi rustylt2...
My advise is to remove the old tiles and make good the walls...tiling onto tiles isnt the best method.....you should never use P.V.A. to prime walls....always use a suitable primer...i use bal prime APD and bal bond SBR follow intructions on the bottle......
Here's the reason why not to use p.v.a......................
http://www.tilersforums.co.uk/tiling...s-primers.html