Mastik failing quickly in marble tiled shower

[scd1074]

Hi, I recently had a contractor strip out and replace all the Mastik in my shower as it had failed. It was a very poor job and not colour matched. The new contractor did a good job, or appeared tom with a matched colour (Jasmine) but less than two months on it has completely failed, coming away on all sides in the shower and at the back of the sink which doesn't get that wet. I have done some googling - I am a weak and feeble female so please don't be harsh! - and wonder if it should not be used to seal the tray to marble as it is natural and porous? But what else could be used instead? I cannot recall what type of Mastik it was but I can see that Mapei do one called Jasmine and there is suggestion that a type 1 adhesive (is their Mastik one?) should NOT be used with certain types of marble. He is coming back on Friday but it seems pointless to do the same again if it just isn't going to work. It didn't seem as if he did a bad job so I fear the same will be done again and it will happen again!