Kerdi board adhesive

[Ben Bord]

Good afternoon,
After watching bunch of youtube videos I have decided to use Kerdi boards for my shower. One thing I don't understand is that they refer in those videos to unmodified thinset mortar and modified thinset mortar. After reading few previous treads it seems that modified mortar is S2 adhesive and unmodified is S1. After looking into specific products they don't typically bear this signage either. Can someone please shed little bit of light into what type of products should I use here in UK?
Thank you.
Ben

 

[bobasd]

thinset is only a powdered, cementitious adhesive that comes in bags.
some of it is modified with chemicals with claims for "water proofing"and "stickiness" - some powder is modified by adding latex liquid during the mix.
the resulting adhesive is used for tiling and backer boards.
read the instructions that c/w the boards - they will say whats needed.