How to Decide between Replacing Panels or Coating Over Rust on a Metal Roof

Posted on: 14 April 2016


Metal roofing offers unbeatable reliability and longevity, but only as long as you maintain a strong and sealed coating over the surface of the metal. When the coating wears away and rust sets in, you need to act quickly before the corrosion spreads and creates serious leaks that threaten the rest of your home. Make the right decision between replacing entire panels or simply coating over rusty spots by evaluating the condition of the metal and the severity of the corrosion.

Perforation of Metal

The first and most serious issue to tackle is checking thoroughly for every area where rust has penetrated through the sheet of metal. It's easy to miss loose patches that are still covered in flakes, so let a professional equipped with thermal imaging technology and sensitive probes inspect the roof. Penetrations can't be fixed with a new coating alone, so you'll need to replace each panel that has perforations to prevent leaks. Perforations can't be reliably sealed unless they're as small as a fastener hole, since these products are only designed for fine seams and very small holes.

Amount of Rust

The amount of rust on your roof, no matter how light it is, should also determine what method you use to fix the problem. Since the corrosion residue must be sanded and washed off before any coatings can be applied, preparations for fixing a completely rusted roof may come with surprisingly high labor costs. Paying a crew of metal roof repair experts to spend two or three days just preparing the roof for recoating could drive the cost high enough to make a roof replacement a viable alternative. If the rust is completely confined to a single panel, replacing that panel is also likely to take less time than cleaning and recoating it.

Cause of Damage

Determining why your roof rusted in the first place is essential if you don't think you're responsible for fixing the damage. For example, a two-year-old roof that is already rusting is likely still under warranty. There's no reason to pay for repairs out of your pocket when the problem lies somewhere in the manufacturing process of the particular panels on your home. If it's a manufacturing defect, it's unlikely that coating alone will fix the problem. Contact the company and request replacement panels instead of just trying to cover up the premature damage out of your own pocket.

Other causes of premature roof rusting include these:

  • hail and falling branch damage that scraped away part of the original factory coating
  • use of a metal product or secondary coating designed for a very different climate
  • failure to stick to the cleaning or recoating schedule recommended by the manufacturer
  • poorly sealed openings around fasteners
  • missing bars and sealant tapes at the seams between panels.

 Coatings are only an appropriate fix if you can fix the other issues that triggered the early rusting, or the new coat won't last long at all, either.

Color of Material

How easy is it to find a coating product or a replacement roof panel that exactly matches the color of your current metal roofing? Before you assume it'd be easy, make sure to actually check what's still available on the market. Products come and go very quickly in the metal roofing industry, so you may be stuck with changing the entire color of the roof with recoating regardless of which repair method you choose. Stick with coating in the first place if the rust is light enough and you can't find matching roof panels.

Addition of Mildew

Finally, advanced algae and mildew growth on the roof's surface further complicates the repairs. These tiny organisms weaken the roof's coating and create openings where rust can develop, so it's essential to clean, preserve, and coat the entire roof if it's covered in algae and mildew. This is recommended even if you have to replace a few panels because the rust created leaking perforations or you'll be facing more rust on the other panels after just a few years.

For more information about metal roof repair, contact a service in your area.