"My stone fireplace goes halfway up the wall and has plaster on wire lath from the fireplace opening to the ceiling. I'd like to replace the plaster and lath with a non-combustible wallboard for a more geometric, boxy appearance. The wallboard would jut out about 5" from the wall, so there would be some corners to deal with. The building code requires no combustible material within 21" above the fireplace opening. Would Durock or a similar product be suitable? If so, what tape can be used at the corners and can some kind of compound be used to feather it in? Can the Durock be painted with flat latex wall paint to match the walls in the room?"