Bare Aluminum / Galvanized Aluminum Roof Cleaning

Hi there, I have a reasonably large 850 sqm aluminum roof to clean. It cannot be confirmed to me whether the roof is galvanized aluminum or bare aluminum. It is not painted.

Which product do you recommend for this cleaning job? 0.5% SH with surfactant? Or truck style wash only / soap and brush? There is some lichen on the roof sheets, skylights and especially lichen is visible on their solar roof piping to heat their indoor pool (black rubber).

Any advice would be much appreciated.

I have a lot of experience with metal roofs but not galvanized. I remember seeing a YouTube video a while back where someone used too hot a mix on galvanized and I’m not sure if they left it on too long or it was too hot and baked right on, but the end result was that it permanently changed the color of the area of roof they did before they noticed and stopped. It’s been a long time since I saw that video but it stuck with me. Can’t find it right now unfortunately.

With that in mind here’s what I would do…

NUMBER 1 WITH A PIN IN IT IS TO SET THE PROPER EXPECTATION BEFORE THIS JOB IS STARTED. Let them know you are willing to give it a go, and will do a small area first to see how everything reacts and will proceed if both of you are happy with the outcome.

Blow off all loose debris and clean the gutters.

Clean up stuff below on the ground you blew off.

Look at plants or anything important they don’t want messed up at roof line. Keep in mind, with metal roofs the water can get rolling downhill fast enough so that it just Cascades right over the gutters so pre wet (pre during, post) everything!

Inspect the skylights. Take pictures. A lot of skylights have busted seals, and moisture. Document that before you spray on them. I inform customers that I don’t really want to test their skylight seals, so what I do is I will peel off the growth by hand as best I can, hit with a 3 percent mix, and light rinse. That way the stuff is dead, but you aren’t hammering that thing with pressure getting it off. It will fall off with time, and if not, you can rinse it again later in the season.

Wet this whole roof down with water. You want to cool it off completely, and keeping it cool is the name of the game.

Do a single row panel or two at first. Preferably on the less visible side of the roof. Use a real light solution. I’m talking house wash light. Maybe less in a pump up sprayer at first, like .5 percent. Let it dwell a few minutes and then rinse with something like an m5ds so you can adjust pressure on fly if needed, but it shouldn’t take much. Afterwards rinse rinse rinse. Let it dry and see how it compares to the rest of the roof. Either proceed or decide against it.

If you choose to proceed, work on the dry side and only work 3 or so panels at a time. Keeping room to be able to always be on dry metal. Use a brush (soft bristle deck brush) if needed but water should be good enough most of the time.


Did a galvalume roof a few weeks ago that was pretty dirty. 2 coats of hw mix about 5 min apart and about a 600psi rinse cleaned it pretty good. However both on painted and the galvalume have found that just running a soft brush over it, not scrubbing, just stick up there and pull it down, improved the results.


Looks good. Any rinse in between? Or just 2 coats 1 after the other?

just one after another, may not even be 5 min. Don’t let it dry on there and if it’s hot, pre-wet to cool it down.