Corrosion Issues/Help

[badtoytrd]

Well, I started to prep to paint the underside tonight and knew that I have a bit of corrosion under the rear door on my 2011 Fleet so I decided to remove the trim and have a look. AHHHHHH, worse than I thought. It appears that when FWC installed the siding they used staples (steel?) to hold the siding until the trim pieces could be installed. To make things even better they used foam tape to "waterproof" the trim and staples. These two things compounded to corrode the aluminum siding. My question is....does anyone have a good way to stop and treat aluminum corrosion? I believe I can treat this and repair before it really spreads but I am hoping someone has used a product that works and can assist. I am also posting as a warning to those of you who have not looked under your trim.

 

[ckent323]

I see that your location is VA. I wonder if road salt and water could be the real culprit here. It is my understanding that alt water alone does not corrode Aluminum because of its neutral pH. A saltwater solution can, however, be a major facilitator for galvanic or dissimilar metal corrosion, in this case between the steel staples (Zinc plated or not) and the Aluminum).
If it actually is galvanic corrosion due to salt water I think you need to get the rusted steel staples out as I believe they will continue to corrode and then seal against water (3M-4200 sealant or equivalent).

https://www.fastenal.com/content/feds/pdf/Article%20-%20Corrosion.pdf

Without the presence of salt water the Aluminum and Zinc plated steel staples should not be too much of a problem.

I live out West and had a 1984 FWC Keystone that I sold several years ago to a young fellow that planned to refurbish it. It had some water damage and mold issues (condensation and pinhole leaks in the old canvas) but it did not have severe corrosion like that.

Perhaps there is a Mechanical engineer or someone with metallurgical knowledge that will read this who knows more than I do about what might be happening.

Craig



https://www.fastenal.com/content/feds/pdf/Article%20-%20Corrosion.pdf

 

[badtoytrd]

Craig,

Thanks for the response. Yes, I am in VA and am the 3rd owner of the camper. I personally have removed the camper over the winter but I can't speak for the other owners. From what I have seen while completing maintenance, they were not as particular as I am.

I completely agree that the main issue is caused by the staples and I spent about 2 hours tonight removing all of them. After I treat the corrosion (hopefully with something recommended here) I am going to install new trim with butyl tape and then seal with 4000 or DIcor (little more maintenance friendly).

 

[ntsqd]

Can't help with stopping the existing corrosion from progressing beyond saying that it needs to be sealed off from oxygen. Perhaps something like POR-15 or a similar moisture curing polyurethane coating?

If you look up a Galvanic Potential chart you'll see that zinc is pretty close to aluminum. Galvanized steel isn't going to set up a battery with aluminum without something pretty serious driving it. Breaking the electrical connection is definitely the first step.

 

[ckent323]

On my Dad's boat we use Ospho on rusty metal (steel and Iron). It inhibits further rusting and seems to work well. We use either Rust-no-more or POR-15 for painting treated rusty surfaces.

Once the Steel is removed there will be no more rusting or corrosion of the Aluminum. The galvanic action will stop. However, sealing to keep out water is still appropriate.

I have seen frequently seen zinc fasteners rust in salt vapor environments which is why I suspect road salt water. Not infrequently the thin plated zinc parts do not have enough coating to protect the steel or the trhin Zinc plating is compromised when the fastener is installed tus exposing the Steel which happily rusts. The hot dipped Zinc fasteners perform much better (but I have never seen a hot Zinc dipped staple). ;-)

I think once you get rid of all the staples life will be better going forward, assuming all that is left is aluminum..

Which begs the question, how does the Aluminum look around all the steel screws in the camper? If it is only at the staples I would wonder why only there and not at other steel to aluminum interfaces (maybe closer to spray from the road in Winter?).

Craig

 

[badtoytrd]

Thanks for the Ospho recommendation. I remembered this product as I was doing some research. The rest of the screws look good and the problem only seems to be along the lower trim. I am in your camp of thinking that the previous owner/owners left the camper on over the winter and the dreaded road salt got to it.

 

[JaSAn]

On my Dad's boat we use Ospho on rusty metal (steel and Iron). It inhibits further rusting and seems to work well. We use either Rust-no-more or POR-15 for painting treated rusty surfaces.

Ospho will work with aluminum but POR-15 is a ferrous metal treatment, not intended for aluminum. The Ospho will need to be coated with a protective coating (paint should work).

Once the Steel is removed there will be no more rusting or corrosion of the Aluminum. The galvanic action will stop. However, sealing to keep out water is still appropriate.

Not true. Bare aluminum will react with the chlorine in salt water: the chlorine anions prevent the formation of the protective alumina layer on the surface, leading to oxidation from dissolved oxygen. Removing the dissimilar metal will slow the process down but not eliminate it. Also any alloys or impurities in the aluminum can create galvanic cells in which the aluminum is the anode.

I think once you get rid of all the staples life will be better going forward . . .
Which begs the question, how does the Aluminum look around all the steel screws in the camper?

I also suspect road salt water; the salt water got in and it stayed wet for a long time. I kept my camper on one winter and have a lot of pitting on the exposed bare aluminum door and window frames in just that one winter. Rust stains around the screws, but no apparent additional damage. My guess is that it is trapped salt water that is the problem here.

jim

 

[Wallowa]

Interesting and informative...do have a question concerning this statement:



"Not true. Bare aluminum will react with the chlorine in salt water: the chlorine anions prevent the formation of the protective alumina layer on the surface, leading to oxidation from dissolved oxygen. Removing the dissimilar metal will slow the process down but not eliminate it. Also any alloys or impurities in the aluminum can create galvanic cells in which the aluminum is the anode."

Aluminum Oxide is very tough and the outside of Al SCUBA tanks in sea water will form this oxide which stops any further degradation [oxidation] unless oxide is gouged or scrapped off...

But hey, I could be wrong...

Phil

 

[badtoytrd]

Thanks for the help guys. I finally removed all of the staples this evening, cleaned it with a vinegar/dish soap mixture and then when over again with denatured alcohol. I will treat with Ospho and then spray with paint. I am planning on replacing all of the screws with aluminum pan head screws. They are a bit pricey but it should stop the mismatched metal issue.

 

[ntsqd]

FWIW POR-15 is a moisture curing polyurethane paint and is not exclusively for use on steel. Nothing in their FAQ's suggests this, though they do mostly talk about steel. Correctly prepped it will adhere to most any surface. I have used it with fiberglass cloth and have some drip stains on concrete that I can not remove.

 

[JaSAn]

Aluminum Oxide is very tough and the outside of Al SCUBA tanks in sea water will form this oxide which stops any further degradation [oxidation] unless oxide is gouged or scrapped off...

Chemistry is not my expertise, so this information comes from a conversation with a chemist when asking why my Grandby's aluminum door skin was rotting away on the bottom. If I remember right the presence of chlorine inhibits the bonding of the AlO2 to the aluminum substrate (the protective layer does not adhere). This allows oxygen to continue to attack the aluminum. I did not have the presence of mind to as how we get from chloride to chlorine.

I was also under the impression that the AlO2 creates a protective surface and so was confused that the aluminum skin had rotted away, but the areas around the aluminum frame where steel screws went into the frame did not appear to show galvanic corrosion (any staples had dissolved). Hope we have a chemist in the group that can clear up any mis-information.






jim

 

[JaSAn]

FWIW POR-15 is a moisture curing polyurethane paint and is not exclusively for use on steel. Nothing in their FAQ's suggests this . . .

You are correct, although all their literature talks about is preventing rust. I'd be careful using it as it outgassed iso-cyanate, which will damage your lungs if breathed in. I use a fresh air breather mask (not just a filter) when painting with it. Tough stuff though.

jim

 

[Bigfoot Dave]

I don't know what it is but there is a product that is sprayed on the backside of aircraft aluminum to prevent corrosion, especially float planes used around salt water. Anyone know more? Thanks, Bigfoot Dave

 

[ckent323]

Dave,

Are you thinking of chromate conversion coat - e.g alodyne?

or perhaps a spray on product like corrosion X?

searching on those I found the following:
http://www.ebushpilot.com/seasalt.htm


Craig

 

[PaulT]

Could it be Boeshield T9 by Boeing? https://boeshield.com/
Or perhaps Corrosion Block? https://www.blockcorrosion.com/main.sc

I have used both of these on my salt water fishing boat & gear with some success. If you have a problem with road salt, washing down the affected areas with either Salt-Away or Salt Terminator may help. I use either one of these to flush my aluminum outboard after each use in salt water.

Paul