When biomass and waste fuels are burned, alkalis and chlorine may form corrosive vapors and deposits, which can cause corrosion of boiler refractories. A lab. method for studying refractory deterioration at temps. and conditions relevant for biomass and waste fuel combustion was developed. Alumina refractory samples were exposed to a K2CO3-KCl mixt. at 800 and 1000 °C for 168 h. Different approaches to analyze alkali penetration into the refractory material were tested. The infiltration of potassium into the refractory was detd. by horizontal and vertical line scan analyses and area analyses of the sample cross section using SEM with energy-dispersive X-ray anal. A descriptive anal. of alkali infiltration mechanisms was obtained by applying Xphase spectral imaging software. Addnl., X-ray diffraction analyses of the cross section were made before and after exposure to detect new phases. The method gives detailed information on the alkali penetration and the mechanism behind it and can be used to est. and compare the performance of refractories in various biomass and waste combustion conditions.