Staining after oxidized metal siding wash

Wall of text incoming:
I recently got a job from a return customer to wash all of his church buildings. Pretty much all of them are aluminum siding that is heavily oxidized. I started with downstreaming 50/50 and had to go over one area multiple times but I didn’t see any spotting after doing a couple of test spots so I proceeded with the rest of the wash. Entire back goes fine but I go to do the front of the main chapel and after washing with 3gal of sh in a 5 gallon bucket, I get these weird brown streaks.

I thought it was rust stains but it happened les so in a more inconspicuous are under a window but I could mostly wipe it off with my finger there which made me think it wasn’t rust(oxidized paint came off with it took but not down to metal).
Anyone have experience with this? I plan on using a brush and water first then moving on to brush and degreaser or gutter grenade then assuming it’s actually rust stains that were covered by oxidation, I was going to try oxalic.

I explained to them that it was heavily oxidized before hand and showed them what happened and they said just do what I could for it. This is my first real commercial job so I gave them a good price and also they’ve sent me a few other biggish jobs and have been great clients, don’t want to let them down now.

I’m going to be getting this Extension pole tomorrow unless anybody knows of a better one from a box store?

Thanks for any suggestions/help!

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i would try re washing with your house wash mix first…then rinse rinse rinse.

Start with that… but it does appear to be “rust stains” from the vent…also if your getting it under windows and it’s not “dirty water” it’s also probably rust stains from the flashing.

Stains may not have necessarily been there, SH is a corrosive and on old rusty metal it can remove some from the surface and then dry on the siding like you have.

Being that it’s aluminum…I would be very cautious on what you spray and brush on the siding for trying to remove them. Acids/Gutter grenade…ect has the potential to strip paint.


SIMPLE GREEN safe for alum siding? I read it is recommended for oxidized alum siding, it also has oxalic acid, which is used for rust stain removal.

Maybe it looks worse in person than in the pic, but personally, I would be inclined to tell the customer, “Due to the age and condition of the siding, this is the best I can do without risking further damage.”

At most, I would rewash with house-wash mix and rinse very carefully to avoid more weeping.

Don’t wash aluminum siding ever again. Easy.


I was extremely selective with aluminum this year. We ended up washing 1 out of 6 aluminum houses estimated 14 total out of 84 requested.I had to tell 70 people its not worth it. I’m at the point where next year, especially during the peak, I’m banning aluminum completely. its just not worth the risk. Not to mention the results are seldom as dramatic of an improvement as our customers expect.

There’s rarely any change at all! Often the “dirt & grime” is the coating so thin it’s showing the aluminum underneath. And you deal with mess like this. I washed one a couple years ago that didn’t look one bit different than before I started. Lol. Aluminum siding is awful.

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The one exception I will make is for what I call imitation vinyl. I call it that because I don’t know its actual name. Whole pieces of aluminum but with a vinyl siding pattern on the home. I’m yet to run into any trouble with it and its always cleaned up nice. We have one Saturday Ill try to remember to get before and afters and post. You would never guess its aluminum until you knock on it.

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Agreed aluminum siding is the worst. I’m pretty much done with any aluminum except for this problem spot though. Just have the metal buildings and some concrete to finish up tomorrow, will report back results, thanks!

We’ve washed two houses with this type of aluminum siding this year and they both turned out great. I got real worried after we booked them when I started reading about all the horror stories with aluminum siding.

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Never know its aluminum until you touch or knock on it
Cleans up decent though