Many thanks to those who have replied. It has helped. I guess it's an area both of differing experiences / opinion and maybe a number of different ways of achieving the same thing - you can see how I could get confused.
But I will do the light grinding (glad to hear 1 mm may be more than needed) and use probably P51 as the original screeder suggested, or ask carefully why the profession that I will have tile the floor, thinks another primer is better.
I'll also have a decoupling mat and see if the tiler agrees on a gypsum based adhesive for the mat and then cement based above mat to stick
tiles with.
Can't do much more.
