Ive just knocked out an old fireplace and want to quickly cover it over. Im back to the brick around where it was and was thinking of cutting a piece if plywood to fix over the whole thing (screwing it to the wall) Is it possible to then apply a thin amount of ready mixed plaster over this to meet the originalplaster around the edge? Id then eventually think about paining it over with emulsion in a few weeks when the plasters dry. It doesnt have to be a very exact job, we just need to cover over the gaping whole and exposed brickword for now!