There is no such thing as a waterproof adhesive, A dispersion (tub) adhesive are classed in "AA" or "B".
The AA adhesive is for the wet areas, but it doesnt mean its waterproof. it means that water will enter it, pass through it without breaking down the structure of the adhesive, thats why a tanking system should be done to protect the background.
The class B adhesive breaks down when water penertrates it therefore resulting in tile failure.
Super grip is a class B adhesive and should only be used in dry / occasionally wet areas, this is because it has acrylic compounds in.
For persistantly wet areas use AA with tanking.
Im not saying or promoting palace in any way, just saying what i use,
Leatherface, if you want to send me a pm ill let you know about bulk buying prices if your interested, but got to be a bit carefull about telling everyone on here as they dont normally supply to tradesmen, only to shops