Help! A couple of years ago we had a professionally fitted woodburner. The chimney breast plaster cracked and the company accepted responsibility. It has taken 3 visits to rectify the problem by fitting stone slips and they said all we had to do was rub down the plaster where it was joined. Having done this it is still a mess where they have used a silicone filler, on the new stone slip, on top of wet plaster. The plaster has tiny air holes in it.
I don't want them back again and thought I would fill the rough area myself but don't know what to use as it is not large enough to plaster. Can anyone recommend a heat-proof filler which can be sanded smooth?