Hello every body. I've been our of tiling business for years just start a mear to work in it again and trying to take bigger jobs step by step, all has change a lot and I'm trying learn as quick as I can. The question, I have to tile 40 sqm aprox porcelain tiles, not know size yet but nothing not to big at the moment, on top of an old concrete that looks paint in black ( bitum?) On top of probably 20mm jakoboard , my questions , how to deal with this "paint ", looks thin, decoupling membrane on top of the jakoboard ? Joint for contraction? Thanks in advance ! One never have to stop learning !