34 replies to this topic

[buckland]

Just an update. Been pretty busy since the storm (yes we are down to snowbanks!) as there was a lot of tree limbs and whole trees snapped, s lots of winch work and chainsawing. BUT today is a warm 70! and thought I'd start pulling some of the screws out of the back wall. My heavens ... I would not think it possible in 12 years (the camper has been in a barn in winters until this year) that galvanized screws could degrade so fast and thoroughly. So I intend to paint all the heads white and use most likely a 10 rather than an 8 ... each one thread dipped in sealant. Interestingly none of the screws elsewhere show any sign of rust, just that back wall (though not the ones surrounding the propane door)

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[ckent323]

buckland,

I have seen that issue before but I don't know the actual cause. 

I note that those fasteners are rusted full length.  When installed they are screwed through a thin sheet of Aluminum and into an Aluminum tube with a relatively thin wall.  There should be an area near the tip that has no contact with the Aluminum.  I would guess that only a few of the threads are actually in contact with Aluminum.   

The coating on galvanized fasteners is Zinc.  The Zinc coating is thinly plated on cheaper fasteners and hot dipped, creating a thick coating, on more expensive fasteners. Zinc is pretty close to Aluminum and should result in minimal galvanic corrosion of the Aluminum.  Also, the Aluminum will corrode in the presence of an electrolyte not the galvanized steel.

However, if the Zinc plating is very thin (as on cheaply made fasteners) it may not offer much corrosion protection.  Indeed, the act of screwing them in may cause the plating to be scraped away in places and the bare steel will subsequently rust.  I suspect that is what is happening since the entire fastener is rusted.  However, I would also expect to see areas where the Aluminum is corroding from contact with the bare steel (where the Zinc plating is gone).

Do you see any areas of Aluminum corrosion at the screw heads?

Speculating on other possibilities / contributors - if your barn is unheated the metal of the camper will heat and cool with the seasons and it is possible in your local environment that condensation develops on the camper and that is leading to the corrosion. 

Are there animals in the barn where your camper is stored?  I ask because their urine contains organic salts which can be very corrosive.  Seasonal weather could cause evaporation and subsequent condensation of small amounts of the animal urine (likely highly diluted but still salty).

It is also possible that the fasteners are not actually galvanized but painted or powder coated in which case they would rust.  Again, though it seems that there should be some signs of aluminum corrosion as well.

It may be that you will actually get better performance from 316 stainless fasteners, particularly if there is a paint or sealant barrier between the fastener and the Aluminum.  If you do go with stainless fasteners be on the lookout for corrosion of the Aluminum under the fastener heads.  If that is happening is is probably also happening to the Aluminum frame tubing at the thread contact points where you cannot see it.

I wonder if FWC has any insight into this or if they would reveal the manufacturer or at least the coating thickness on the fasteners.  That information would probably be useful in sorting this all out.


I hope this will be helpful and I look forward to learning how this all plays out over time.

 

 

Craig

Edited by ckent323, 15 April 2023 - 11:22 PM.

[PaulT]

I'd blame it on Massachusetts winter roads. My in-laws gave me a 1996 Chevy S10 they were given by a friend in Conway who passed in 1998.  I needed brake work on it in Oregon in 1999 and had a tough time getting any Oregon mechanics to touch it. The beatings I took for everything being rusted due to road salt were brutal.

 

Oregon has just recently begun to use road salt so the hue and cry from mechanics should begin here soon. 

 

Paul

[buckland]

Craig, You bring up a bunch of good questions and I agree with you, especially our NE seasonal changes in a real barn (heated?!) would have enough moisture swing that it still got wet, The road salt here can be crazy where I have to sweep it out of the garage which has fallen off the truck. I am curious about which screw type will be the least reactive. So I will do some of both and most likely go to #10 as the aluminum frame I can't see no doubt has screw holes which oxidized and are brittle. Glad I am a type A at times as Buddha would say "the best time to cut down a tree you don't want is when it is 3" tall"... think forward.

[buckland]

Paul the salt is crazy bad on vehicles. They dissolve. Places have looked into a barley sugar that melts snow (smells like beer too!) Amherst College uses it on all walk paths. I spray the undercarriage of my truck every fall with a lanolin coating called "Fluid Film" ... stuff is wonderful. A quart (2 first year) each year.