A vestibule block or interior furnace wall utilized in a diffusion furnace for manufacturing semi-conductors, integrated circuits and the like, and which is made of refractory or ceramic material, is treated on its surface with a suspension of fine particulate of a glass frit composition comprising an alkali earth metal alumino silicate, and is thereafter heated above the transition temperature of the alkali earth metal alumino silicate. Vestibule blocks and interior surface walls which have been treated in the above-described manner are highly abrasion resistant on their surface, generate virtually no particulate matter under conditions of ordinary use in the semi-conductor manufacturing processes, and generate significantly less particulate matter when tested in an abrasion test against vestibule blocks of the prior art.