Is a primer necessary?

Hello,

in 6-8 weeks we can start laying tiles and wallpapering in our house. Now I wanted to prime all ceilings, walls, and floors where tiling and wallpapering will be done with the bonding and protective primer PCI Gisogrund. Some say that it is enough to paste the walls and ceilings beforehand and that it is not necessary when laying tiles either. There is underfloor heating throughout the house, walls and ceilings will be plastered.

I would like to hear your opinion on this.

I have never heard that primer is used before tiling! I didn't do it back then either (tiles on 50 sqm are still there after 14 years :))

Just quickly googled, your paste is used for adhesive residue!