Sound technical content, curated with aloha by
Ted Mooney, P.E. RET
Pine Beach, NJ
The authoritative public forum
for Metal Finishing since 1989
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Preventing electro galvanic reaction between aluminum and steel
Q. Can somebody please advise me on how to prevent the electro reaction between mild steel structures and aluminum components mounted onto such structures?
Your advise will be greatly appreciated.
DRIES GROENEWALDelectric distribution- JOHANNESBURG, GAUTENG, SOUTH AFRICA
2003
A. Hi,
What is corroding, the steel or the Aluminum? Aluminum will protect Steel locally. If the steel corrodes, pretreat and paint (or galvanize)it before assembling the Al fixtures, and use the correct nuts and bolts. If the Al corrodes (as well), you are probably working in a marine environment. Avoid cast Al and anodize or chromate and paint the fixtures. Anyhow, putting an electric insulator between the structures and fixtures could only improve the situation.
Good Luck,
Peter Piessens- Bertem, Belgium
2003
Q. Hi There
I will be fitting an aluminium downpipe 0.8 mm thick to a mild steel gutter 2.0 mm thick and would like to know if either one will react negatively. I was planning to put in rubber sock over the steel spigot will this help?
sales manager "gutters" - Cape Town
February 19, 2010
February , 2010
A. Hi, Mark. Galvanic corrosion cannot occur unless there is actual metal-to-metal contact because you need a flow of electrons for it to happen and electrons flow only through metal, not through liquids. So, if your rubber sock prevents metal-to-metal contact, you are fine.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Corrosion on beams in ceiling under garage
Q. We have a room under our garage. The ceiling is covered with insulation with what appears to be aluminium foil backing. Lately the insulation seems to be rotting away where the steel beams are and some rusty colored gritty stuff has seeped through and upon inspection, the steel beams look rusty, but not cracked. We do not have any water leaks. Is this a chemical reaction (steel touching aluminium) ? Should we remove all the insulation? If so, what would be best to replace it?
Elleen Haggerty- Pittsburgh Pennsylvania usa
October 4, 2019
A. Hi Eileen. Aluminum foil does not cause galvanic corrosion of steel, but it can help retain moisture which does lead to corrosion. The foil belongs on the "warm" side of the insulation, for example, it faces the open attic not the roof; it faces the ceiling of the living space, not the open attic; and it faces the floor of the living space, not an open crawlspace.
I don't know what kind of "room" is under a garage because I don't recall having ever seen one, and most garages are unheated spaces, so I can't say which side is warmer and whether the foil on the insulation is correct or backwards. In any case, garage floors get wet, sometimes they receive acid treatments, and chemicals are often stored ... so galvanic corrosion is the last thing I would suspect as the cause of the rusting. Under the circumstances it seems the steel beams should have been painted to deter rust. Good luck.
Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
October 2019
Q. Thanks for your quick reply! I guess I didn't give a very accurate description of our home. The garage is next to the house on the first floor and underneath it the laundry room. It is on the same level as the basement. The insulation is on the laundry room ceiling and the pink side is facing the garage floor and the foil on the insulation is facing the floor of the laundry room. So it's on the warm side. Hope this helps.
Elleen haggerty [returning]- Pittsburgh Pennsylvania usa
October 6, 2019
A. Hi Eileen. Laundry rooms, especially in a basement, are somewhat corrosion prone due to the humidity, bleach vapors, etc. Some surface rust on a steel beam is not a cause for concern, and the foil is not causing it except in as much as it may be helping to retain moisture.
If the insulation is badly deteriorating and was installed correctly, I'd bet that you once had a leak or overflow even if it's not leaking now. Kitchens or bathrooms are often over laundry rooms.
Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
October 2019
Q. I would like to replace steel windows with Aluminium windows.
Will there be any metallic reaction if I left the steel frame in the wall. it may come into contact with the aluminium frame.
- south africa
November 15, 2019
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