Fireclay Firebricks

Firebricks line kilns, forges and furnaces because they stand heat that would slump or crack ordinary brick. They are refractory fireclay bound round a large share of grog. Potters' guides give about 20–40 % grog for general kiln bricks and up to 60–80 % for the hottest parts such as fireboxes; the bonding clay should be a little less refractory than the grog. Factory firebricks are fired at about 1,100–1,400 °C. Make test bricks first, fire them, and check them for cracks before making a whole batch.