Hello, we have just installed a galvanised corrugated roof and it is already looking like the galv is turning white/powdery in places and the metal underneath seems to be starting to show through. can we paint this without washing and is this normal to deteriorate so quickly - 2 weeks.
Generally for this age of galvanised steel on a roof we would suggest washing down with Rust-Oleum Mathys ND14 Cleaner Degreaser then Rust-Oleum Mathys 108 Surfa Etch Solution followed by Rust-Oleum Mathys Noxyde or Rust-Oleum Mathys Noxyde Pegarust.
However, it seems that the reactions being reported after just two weeks are highly unusual, this deterioration after just two weeks is definitely not normal and we would recommend seeking advice from the installers/manufacturers to gain more information of possible causes and remedies.