i repaired a blokes roof 2 yrs ago, broken tiles pointing to chimney and damaged flashing, then 6 months later when loft has had time to dry out a bit he has me skim the room out, i removed the perished plaster on the chimney breast, wall behind seemed ok, bonded and skimmed it, once the room was dry the customer painted it (the part that was originally perished was still a bit damp), 2 months later the damp has shown thru and has now spread to wall at side of chimney breast, its not bad but its staining thru, the chimney has had one of them nasty galvanised piss pots shoved on top so there is air flow, surely it should have dried out by now, 18 months since i plastered, the guy is ok about it but i am beginning to feel like i've robbed him, i cant come up with a reason, it doesnt look like rain getting in, codensation from inside the chimney maybe. should i have not used bonding in that situation.