Iron ore pellets are commonly sintered in a kiln insulated with bricks, which wear and need to be replaced regularly. It is desirable to increase the lifetime of those bricks. Slag/brick compatibility tests have been performed in a laboratory furnace. Slag collected from a production kiln, three commercial bricks and additions of alkali were used. Alkali dissolves the mullite in the bricks, and form the phases nepheline and kalsilite. Characterization of the microstructure showed that the degradation of the bricks was enhanced by increased temperature and amount of alkali. The slag penetration depth is more affected by increased temperature than increased dwell time.