tiles blown on pipe boxing in bathroom

[jack1111]

merry christmas to you all.
some of the tiles in the bathroom which cover the boxing over the waste pipe and hot and cold pipes have blown, some have come unstuck and the others the grout has cracked
the bathroom has been in for 3 years without any problems, i removed some of the tiles and what i think is ply is damp, i have checked for any leaks so can only think its from the shower and the water has got underneath them somehow?
can you guys suggest the best way to sort this out, i know i need to restick them but do i need to replace the ply first or can i tile over damp? its not wet.
also how can i remove the old adhesive from the tiles? to restick them. id rather not have to buy more tiles and cut them as i dont have the cutter.
i tried to add a picture but would not allow it
any advice appreciated, nice one cheers

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[jack1111]

come on guys i need your help

 

[rjm2k]

To remove the adhesive you can soak them in water for a day or so then scrape off

 

[jack1111]

ok mate will give that a go, can i tile on to wood that is a little bit damp i know its not ideal but i dont want to replace all the ply.
can you recommend a adhesive that will be water proof and not crack as there are pipes under it and i think thermal expansion is a problem.

cheers

 

[rjm2k]

Not sure about the ply, best try let it dry to see if the issue is still there.