Galvanized Roof Rust

The roofs i have done have lasted a minimum of 20 years now.

Galvanized roof rust.

I have used both regular paint and roof coat on old metal roofing with pretty good results. I like the fiber in the aluminized roof coat as well as in the black nearly tar roof coat. Rust is the reaction of oxygen moisture and metal that results in reddish brown blotches. Most metal roofing is made of galvanized metal or coated to prevent rust from occurring but standing water and the heat generated by direct sunlight can wear the roof s protection away.

Rust corrodes metal and if left untreated it can cause. Galvanized metal roofs are coated with a layer of zinc that inhibits rust. Left untreated white rust corrodes the zinc and the metal underneath begins to rust exhibiting the more traditional brownish red color. Galvanized metal is coated with a layer of zinc to protect the iron or steel underneath.

But galvanized metal which exhibits a shiny adherent but rust colored stain is not truly rusting. Rather this is just a phenomenon that often occurs in galvanized materials due to intermetallic alloying of iron and zinc i understand and is not indicative of the end of the useful life of the galvanizing. Unfortunately over time this coating can fail leading to minor rust outbreaks. If the item is exposed to continually wet conditions the zinc develops a film known as white rust.