Commercial ceramic candle filters were exposed to harsh environments to determine the effects of alkali and steam on their long-term durability. Ceramic candle filters are composed of relatively coarse aggregates fixed by a ceramic bond. The filters studied include a clay-bonded, granular aluminosilicate candle and three types of clay-bonded, granular SiC candles. The alkali, steam, and steam-alkali corrosion of these commercial ceramic candle filters was examined at temperatures ranging from 450 to 1225°C and pressures up to 1000 psi. Results indicate that the aluminosilicate candle filters perform better than filters made from granular SiC. The SiC filters show binder degradation in steam as well as in alkali-containing environments at temperatures as low as 700°C, with oxidation of the SiC occurring in the steam environments at higher temperatures. Sodium and potassium contaminants in the steam atmospheres accelerate the degradation of both types of filter material.