Patent ID: 8039048

Claim:
A process for producing algae-resistant roofing shingles, the process comprising producing algae-resistant roofing granules, and adhering the granules to a shingle stock material, the algae-resistant roofing granules being produced by a process comprising: (a) providing inert base particles; (b) forming first intermediate particles by coating the inert base particles with a first mixture including; at least one algaecidal material, and a void-forming material, the void-forming material releasing gaseous material at temperatures above 90 degrees C., and having an average particle size no larger than 2 mm, to form a first layer on the inert base particles; c) forming second intermediate particles by coating the first intermediate particles with a second mixture including a coloring material and not including a void-forming material; and (d) heating the second intermediate particles to decompose the void-forming material and form pores in the first layer to produce the roofing granules.