Grout coming out and crackling noise under some tiles

[Ajax123]

This is a question so go easy.
If the floor is primed correctly then in theory it shouldn’t matter if you use cementitous adhesive over gypsum based as the primer is separating the adhesive from the substrate. Am I mistaken?

The only issue with this system is that but leaves little room for error. You are correct in that if done properly it will work. If on the other hand it us not then it is prone to failure. If using cement based adhesive I would recommend a water based epoxy primer

 

[Dumbo]

I haven't done yet, but I was pricing a large floor a few months back that had a lot of hairline cracks in it and I priced for uncoupling in that instance. Incidentally my caution more than likely made me too expensive as I didn't get the job but I wasn't going to risk it and tile directly to that particular screed, not worth it.

I'm with you .
If I lose a job so what .
Customers want to cut corners on the. Price then expect you to put it right if it goes wrong