Contrary to popular belief, some aluminum alloys are subject to corrosion, as is the case with aluminum chimney chase covers.   Chase Toppers only uses high quality, high grade stainless steel and copper for our custom chase covers, crown covers, and chimney caps.   We cannot put our lifetime guarantee on an aluminum chase cover, therefore we do not sell them.   Here are some examples of the corrosion, commonly called "pitting" that affects aluminum chase covers.