Builder packed with (a lot) of adhesive

Usually, adhesive gives the "maximum depth" information on the bag. Just like with any product, different brands have different tolerances or qualities etc. Personally, I would have said that 40-50mm to hold Marble is too much unless it is very specialised adhesive and states it is safe to do so. With the tiles I install, I wouldn't try to over come this issue with packing out. I would have studded (if required) and plaster boarded the wall to bring it back to level. The problem with tiling onto a plasterboard wall is that I think the maximum weight it will safely hold per square meter of tiles is only about 35KG. If you do have concerns, I would suggest trying to find the manufacturer of the adhesive to find the maximum depth and the manufacturer or supplier of the tiles to find the weight per square meter. Hope it helps

every bag of addesive has a limit to the depth...and if it was ready mixed then that will be a problem but check with the fitter what material he used then u can ring the manufacturer to find out the exact limit