Shower wall botched

[Remedy Seeker]

My plumber had to remove some wall plaster to install a new shower tray. Instead of replastering to a flat finish he seems to have infilled the gap but not adequately then covered the patch with waterproof membrane. I can feel a void beneath the membrane and there are even surface undulations on the solid wall parts. I'm just a home owner with no plastering skills but think that this "cave" in the substrate will mean the tiles are floating on just a bit of cloth so likely to move - and give me some awful leaks longterm. Am I right? Any advice gratefully received.

 

[HERTS P&D]

Pictures would help.

Andy

 

[blup]

When you give him cup of tea this morning casually mention it, in the unlikely event he wasn’t going to finish it off properly it will be a reminder.