Hi I've recently had a back boiler removed exsposing a cavity in the chimeny in the front room. The brickwork inside this is conrete bricks on the bottom and red brick on all other sides, the right hand of which is extrememly uneven one brick jutting out 1/2 cm. I want to plaster it so it has clean lines and then tile it at a later date. We will eventually want to fit a wood burning stove or use it as an open fire. My query is: can I use 'normal' under plaster and then 'normal' finishing plaster to do this or do I need a special mix or type of plaster for heat resistance?