Metal roofs took Miami by storm about 10 years ago when a few local fabrication shops developed their own systems, had them tested and approved by the county. Until then metal was a pricey option and only seen on commercial buildings, in Coconut Grove and the Florida Keys. Almost overnight metal was competitive with the tile roofs. Metal roof cleaning in Miami was something we were not really thinking about at the time .
We did not do many metal roofs when RMI started in 2006 but it has snowballed to the point we do several per year. Through the years I’ve noticed something I did not anticipate. Some of these roofs were getting dirty – fast. Not all of them – just the painted ones. The mill-grade roofs were staying relatively clean. All this led me to an obvious conclusion. These roofs weren’t just dirty. They were stained by the same bacteria which eventually turns everything black down here – Gloeocapsa magma.
Mill-grade Galvalume sheets are produced by running a galvanized sheet through a molten bath of 55% aluminum and 45% zinc. It is the zinc which kills Geocapsa Magma spores when they contact the roof. More accurately, the PH of the surface is not conducive to bacterial growth – or algae, mold and fungus. Furthermore, with all of Miami’s flora and fauna, the biocides in the paint used for color on the metal panels are not sufficient to prevent bacterial growth.
I’ll admit, we had never done a metal roof cleaning before I got the call from a gentleman from Kendall asking a bunch of questions. He had been looking at our website and now trusted me to clean his white metal roof. So I looked at some pressure washer websites, made some calls and that was all quite inconclusive. I called the manufacturer and they sent me their suggested cleaning method – scrubbing with a soft brush and mild soap. Pressure-washing was verboten.
I tried it. Let me tell you, I could hear the bacteria laughing at me. This would take forever. My suspicions were confirmed – the manufacturer’s cleaning instructions were just another CYA exercise. I believe the #1 purpose of labels and directions is to protect the company. That’s why they advise two Advil when it takes three or four to work – for me, anyway.
So, I was on my own. This was factory painted metal, right? What could the manufacturer be afraid of? One pressure-cleaning shouldn’t hurt it. Then it hit me, “What do you preach about pressure-washing tile roofs?” Repeated cleaning damages the finish!! I can see how repeated cleaning could, mil by mil, wear through a metal roof’s finish.
We cleaned it the same way we clean tile roofs: Soak the roof with a 50/50 chlorine and water solution – don’t let it dry! Wait 5-10 minutes and pressure wash it off. I use a 2400 psi rig with a wide tip. That’s all you need. Then we spray it with a sealer/cleaner with a 3-yr warranty. Some of these new self-cleaning treatments using Nano Technology really work and are getting better. That is the last time you should have to pressure wash. When it starts getting stained again just spray it.
25 years of experience speaks for me, as do the results of this metal roof cleaning. All the negatives on the use of bleach and pressure washers will be filed right next to the manufacturer cleaning instructions.