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White spots on aluminum scaffolding when stored under cover

I kept my aluminum scaffolding outside on the grass for one year and the surface stayed bright - no signs of corrosion. Then I finally got around to dismantling it and put small parts in a shed, and larger parts under a lean-to. Now after one winter I see all the surfaces are covered in white spot corrosion, with the parts in the shed much worse than those under the lean-to. I guess oiling them will help, but I would really like to know why the corrosion started. The humidity levels in the shed are probably higher than outside, although it is well-ventilated. I store other things in there, including other metals, and some bags of concrete. However all these are out of direct contact with the aluminum parts, and the bags are sealed.

Any suggestions?

Andrew Murray
consumer/homeowner - Roskilde, Denmark
2007

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Are you sure they are aluminum not galvanized? I'm familiar with this problem on galvanized parts where good ventilation is required because the carbon dioxide in the air is a necessary part of building the corrosion resistant skin. If the aluminum parts are not anodized, and depend instead on a natural oxide protection, ventilation may be necessary.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2007

The components are definitely aluminum. But they could have a natural finish.

Andrew Murray
- Roskilde, Denmark
2007

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Try to wash it with 3% borax [affil links] solution,then you can paint it with 2 gm tannic acid [on eBay or Amazon]/1,8 gm phosphoric acid/1 lit water solution(very diluted iron rust converter [on eBay or Amazon] ,but according to some expired US patents it can be used as simple conversion coating for aluminum).When dry you must clearcoat it(or oil or wax)!Hope it helps and good luck!

Goran Budija
- Cerovski vrh Croatia
2007

Solution pH must be between 4-8(!Good luck!

Goran Budija
- Cerovski vrh Croatia
2007