Designing Kitchens and Bathrooms - Plastic Shower Wall Surround Breaking Free

I had a contractor remodel my bath. Took out the old tile shower and base that were completely lost due to previous owners lack of maintenance. He installed new sheet rock, plastic shower base and 5 pc. plastic walls. This was all done a yr ago. The walls are gapping at the base, tearing free of the caulk. I re-caulked and w/in a week they had popped free again. All other areas are secure. I have noticed some flex in the center of the wall sheets. Looks like he was light on the glue. How can I fix this issue? Thanks for the advise.

P.S. The contractor is nowhere to be found. He did have good referals at the time.

hello money pit
Been there!! It could be not enough glue or it could be the glue it self. or some glues wont stick properly to painted surfaces. fixing the problem is tricky very carefully peel off the wall panels and with a sharp chisel perferably one about 2" wide carefully shave off the old glue from the back of the panels.(becarefull not to damage or gouge them.
Then do the same to the walls. Patch the walls where needed.
Go to your building supplier and get Franklin Braand adhesive (make sure you get the type made for tub surounds ) then reinstal your wall panels following the directions on the adhesive tube.

Good Luck