Wood or metal lath or any one of the various plaster boards can be used as foundation.
Plaster for exterior walls of a chimney should be applied direct or on metal lath.
The edges of the metal lath are bound with a strip of wood nailed to the board.
metal lath and plaster or a good grade of plaster wall board is preferred.
If a fireproof cellar is wanted, cover the ceiling with metal lath and a good cement plaster.