Must admit, I wouldn’t have thought twice either
@hmtiling, and with the backing of the adhesive company I use, use cement based adhesive. They have no problem specking their products on anhydride.
In fact just completed a 50m2 floor with 1800 x 900 that was initially a failure due to incorrect prep.
It has expansion joints at the two doorways.
It also has ufh which was initialised in the correct manor and is cranked up fairly high.
It’s a good install and I have complete confidence in it.
Personally I wouldn’t have dreamt of using 5mm joints, 3mm would have been my choice.
I’m certainly not trying to butt heads with you Alan, I’m just saying what I’d of been happy with.
If it is a thin tile, then as Harry says, definitely an anti fracture mat too.
And if water proofing was necessary, I have complete confidence in a waterproof one that I use also.
Obviously expansion joints in this situation are a given, agin tho, I’d of only gone for one.
That would conform to all the relevant information that I possess, so if things in the gypsum screed world have changed, then we as a forum, need updating.