Tile waterproofer

There is a flexible system you can use , but to be honest as long as the tiles are installed correctly there should be no need to do this as the tiling industry was without these types of products for many years before “tanking “ came along . 

There’s many things that need to be considered but if u wish just to obtain correct stuff and fit yourself then you can buy from Vera sur or u may be able to get from a paint shop . 

Pm if u want further advice , don’t forget the adhesive and grout is essential you get the right one .