A kitchen waste pipe leaked at a joint where it passed through an exterior wall, and it's now soaked. So, now there is a tide mark of salts, about a meter high on the inside. We are still waiting for it to dry out, but do we need to hack off the old plaster/render? Or, is there a way to get rid of the salts? Would dry lining be an alternative and if so, with ordinary tapered edge plasterboard or foil backed? Any other way to deal with this?