Screw replacement

[DavidGraves]

In New York people dont drown in the Hudson....they burst into flames.

 

[buckland]

So if all my galvanized on the back wall have rusted (not the small hex head ones holding in the doorframe) then I suppose I don't have anything to lose by trying stainless. Huh.

 

[DavidGraves]

You have a lot to loose by using stainless....galvanic corrosion between dis similar metals in the presence of an electrolyte....H2O....the aluminum looses this battle.

I really think your best bet is Galvanized steel screws with a baked on white finish of the same size as was first used at FWC.

Any failure of the paint finish I have seen is within the socket head of the screw and was the result of the metal drive tool being cranked too hard.....once can drive them with one of the old puny hand held drivers and then do the last 1/4 turn by hand driver.

Bed them in a good adhesive sealant and you will get some good life from the repair...

In the case of a VERY loose fit step up one size in screw....or partly drive in bedding compound and then do another quarter turn the next day.

I have seen a square driver set made of phenolic instead of metal but dont know where to buy it.

The metal drivers leave residue of steel in the square drive sockets and this can then rust.

The screws are a major appearance factor for the camper...they deserve some care so they don't rust .

Did you go to Aqua Caliente in B. C. S. ?

DG

 

[buckland]

Nope. We were fairly close but a long road ahead so had to move on. Thanks for your thoughts on the screw replacement. All screws on back are rusted all the way through....not cosmetic caps. Salt. Wicked heeya in the Bahstin state.

 

[SunMan]

You have a lot to loose by using stainless....galvanic corrosion between dis similar metals in the presence of an electrolyte....H2O....the aluminum looses this battle.

I really think your best bet is Galvanized steel screws with a baked on white finish of the same size as was first used at FWC.

Understand the logic and I can’t explain why it hasn’t been an issue, but I regularly see 3 campers that have been parked nearly ocean front for over 5 years, all screws have been completely replaced with stainless steel with zero hint of galvanic corrosion. Mine is going on two years. In that time I would have replaced the galvanized screws at least once if not more. Just sayin.

 

[DavidGraves]

Its all good....Buckland, now you have an excellent reason to revisit B. C. S. sometime.

BTW did you go to the french bakery in the mining town.....?

Rusting in Oregon....only state where moss grows on anchor wire fencing....and Asphalt....and hard baked metal roofinf. ...and the north facing side of my Toyota.....


DG

 

[buckland]

That we did. We got some donuts from the famous bakery and just down the road got a goat Taco to go!

 

[SunMan]

^^^
Santa Rosalia. Just drove through there last week.

 

[ckent323]

It is true that dissimilar metals in the presence of a corrosive electrolyte (such as water or worse salt water) will lead to galvanic corrosion. However, if the metals do not actually make contact with each other, particularly if they are separated by a non-dielectric barrier (such as many adhesives and gasket materials, then the corrosion will be significantly minimized or even eliminated.

For our campers with Aluminum framing and skin having steel (even galvanized or stainless fasteners) putting a coating of sealant or adhesive or even paint on the threads of a steel screw before it is installed and between the head of the screw and and the Aluminum skin will help minimize corrosion risk. It is likely that applying the coating only under the screw head (or even a rubber or butyl washer under the screw head) would be sufficient since the likelihood of water getting past the seal and into the threads would be significantly reduced.

https://www.marshfasteners.com/can-stainless-steel-and-aluminum-be-used-together/

An FYI relative to stainless steel.

If one is concerned about the fastener corroding then stainless steel is worth considering. However, stainless is still more cathodic than Galvanized steel and Aluminum (which is more anodic) and galvanic corrosion of the Aluminum is still likely in the presence of a corroding electrolyte if a protective coating is not used.

• Anode – material that is positively charged, electrons leave this material
• Cathode – material that is negatively charged, electrons enter this material
• Electrolyte – liquid that aids in the process of electron transfer
• Corrosion/corrode – Destroy or weaken metal gradually

"How It Works
Galvanic corrosion occurs when two materials (an anode and a cathode) come into contact with each other and an electrolyte. Electrolytes can be environmental factors such as humidity or rainwater. When these factors come into play, electron transfer will begin to occur. Depending on the level of resistance in an electrolyte, this transfer can happen much faster. This is why salt water, an electrolyte with a very low resistance, is a common factor when considering what product to use. Due to this, it is incredibly important to consider what material you are going to use in an environment. When working with a marine, salt water environment, you even need to consider the type of stainless steel you are using.
When aluminum and stainless steel are used in an assembly together, the electrons from the Aluminum will begin to transfer into the stainless steel. This results in the aluminum weakening. This weakened aluminum causes it to deteriorate at a much faster rate. This can lead to an extended life of the stainless steel. Note: Aluminum, if left on its own with the electrolyte, will still lose its electrons eventually, but having stainless steel present will significantly speed up this process."
Reference:

https://www.albanycountyfasteners.com/blog/stainless-steel-and-aluminum/#:~:text=The%20combination%20of%20aluminum%20and,)%20to%20another%20(cathode).

There are at least 5 types of stainless and only one type has high corrosion resistance (austenitic).

Austenitic stainless steels generally provide the most corrosion resistance because of their high amounts of chromium. 304 and 316 are commonly used but 316 stainless has the best corrosion resistance, which is why it is widely used on boats in the marine environment. It is also the most expensive stainless.

Other stainless steels can and do corrode.

If the manufacturer does not say is it 304 or 316 then it probably is not corrosion resistant. But when used with Aluminum in the presence of an electrolyte it may still lead to corrosion of the Aluminum.

https://www.kloecknermetals.com/blog/what-are-the-types-of-stainless-steel/#:~:text=Stainless%20steel%20can%20be%20classified,%2C%20durability%2C%20and%20temperature%20resistance.


Bottom line;

For our campers unless the screws themselves are corroding (in which case using 304 or 316 stainless fasteners would help) the best approach to mitigating galvanic corrosion of the Aluminum (and even mitigating steel corrosion) is to use painted galvanized steel screws or insulating washers or sealant under the screw heads (or maybe a combination of these). Galvanized screws and stainless steel screws will not prevent galvanic corrosion of the Aluminum but the galvanized screws should only be a minimal risk.

I hope this is helpful.

Craig

 

[buckland]

I thought that being an old math/science teacher I'd do an experiment. I bought both the 316 SS and the Zinc coated. I am going to use the galvanized ones for the most part but will put in a small amount of SS 316 to see how they do. My screws in the camper now, when I back them out (on the rear wall) are all rusted tip to head. So I'll check them eraqch year going forward and see if either group craps out first!

 

[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)

 

[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

 

[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.