It's crappy job and he didn't care about it, and I'm not suprised; Think you've got bigger problems than the plaster, everything says damp - was this a carpeted larder or loo? Ventilator? So there 's a brick wedged in to support a bit of block, which has then moved when he's tried to troweled off and cracked. It's blocked and has mould so you just want to just cover it up and hide it? The plaster at floor level is crumbling, due to damp I think, you saw it was in bad shape when you took the skirting off but you let him start and expected him to clear it up and fix it for the same price. Walls and ceiling, say 3 bags and some bead maybe £20 out of the 200 and you "took a chance" - why?