ok i bought a nicobond(i think) tanking kit for the best part of £60, i read the instructions and it says if using on porous serfaces i should prime the walls first. im slighty annoyed that after buying "the kit" i have to buy further items now, i can;t think of many walls that wouldn;t be porous anyway! if there anything else i can use pva? i did try a small section with the tanking kit but it appears to just peel off and i wouldn't like to trust tiling onto it. thanks