Painting a Metal Roof
White Roof Cooler
Because we have a flat roof, the roof that was over half of our house was painted white. This was done to lower the summer temperature in the rooms below. It made a big difference.
On a 83 degree day, our black metal roof registered 153 F while the white roof only measured 108 F. Cool roof information.
Metal Rust Reformer
A rust converter is a chemical treatment that turns iron oxide into a more stable form such as iron tannate. The advantage of a rust converter is the treatment is less invasive and the only surface treatment needed is a cleaning of loose rust and soiling generally with a wire brush. Rust converters have wide stretching usage in conservation, they are used from the stabilization of iron based museum artifacts and collections to iron architectural elements and outdoor sculpture.
Our metal roof is made of terne metal. It had been painted over the years with a regular roof paint. Where the metal seams had bent, the paint collected as hard blocks. As you can see from Photo A, the paint had peeled off and the roof rusted. An examination showed that the metal was solid with a few small holes.
The first job was to scrape all of the loose rust, dried paint chunks, and old roof cement. The roof was power washed and a metal putty knife was used to scrape the rust and old paint. Although it isn't recommended to use a metal implement to scrape the roof, it was the only way to remove the loose rust and old paint. You have to be extremely careful not to pierce the metal. Photo B shows an area that has been scraped. During the scraping, straighten up any bent seams.
After the scraping, the roof was power washed using a house wash. If you have moss or algae wash with a chlorine solution.
In Photo C, you can see the two right panels that have been treated with metal reformer (converter). The panels on the left have had the reformer treated areas primed with Preservation Products rust inhibative base coating.
Because the old gutter supports were nailed through the roof, I removed the roof cement they were covered with and then covered them using Preservation Product's Reinforced Restoration System which includes using fiberglass embedded in the coating.
If you find any holes or weak areas, use Preservation Product's fiberglass mesh to strengthen them. See Patching a metal roof.
Metal roofs should be coated (painted) with a specially roof formulated acrylic latex which bonds tightly to metal and becomes a flexible coating 15-20 mils thick. I used Acrymax from Preservation Products.
I used three coats. The first was their basic coating (HP-1000) followed by two coats of HP-5000. These coatings have to be "slathered on" to reach the coverage rate of one gallon per 100 sq. ft. This rate was almost impossible to reach using a 3/4 inch roller.
Preservation Products offers a good description of the advantages of these acrylic roof coatings for metal roofs.
Rust-Oleum Rust Reformer (Selected as the top performer in the study above)
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