Corrosion on the mast between Aluminum and Stainless Steel

[jonahmulski]

Hi,
I'm starting to get corrosion on my aluminum mast and boom around the points where the stainless steel hardware is mounted (see pics). I'm planning on remounting the hardware and would appreciate any input on how to prevent or slow this process from happening again.
Many thanks,
Jonah

[roverhi]

Take off the hardware and use electrical tape, vinyl window material, etc to insulate hardware from aluminum mast. Use TefGel, LocTite, etc on the fastener threads.

Hate painted masts. The corrosion you see is inevitable. You'll eventually want to repaint at great expense.

[Cheechako]

It's common and tough to avoid. I use lanolin liberally on all the fittings and threads to isolate them a bit. There are other products too, I think tough gel? is one. They will come out in the future also if you use lanolin etc. Plastic washers etc may help a bit but the screw still contacts the aluminum.
You may have a very tough time getting those out, be prepared to have them break off in the aluminum.
I had a mast completely professionally stripped and repainted and it looked like yours again after about a year offshore. If I had it to do again, I would leave the mast bare from 6 or 8 feet up from the deck.

[SailingFan]

Rover is right about the corrosion being galvanic. You don't have to spend a ton to repaint though. You can simply sand away the corroded parts, feather the sanded area (that should include enough of the area under the paint to ensure the corrosion is all revealed) and repaint. The mast does flex, of course, so the paint needs to have at least some flexibility, but do not use latex unless you want a long sock to be available one day! Polyurethane based paint could be a good answer, and is only about 30 bucks a gallon (which is more than you likely need). Painting cost will be mostly labor, so like other things, if you are handy, you can save a ton here. While you are up there, check all the other hardware for corrosion and wear, spreader bar patches, radio antennas and wiring, windex, etc., of course. That will save you potential hassles later on. You likely have more corrosion hiding someplace, because that is more than a little bit you are showing in your photos, and suggests there is likely more to find yet.

I am in a similar battle, but have only a waxed finish on my aluminum spars (well, it WAS wax at some point, it is likely about raw aluminum at this point).

[DeepFrz]

Painting aluminum is not quite as easy as SailingFan suggests. Don't forget the etch coat.

https://www.youtube.com/watch?v=CD7f0hhta0Y

[mike d.]

Rap the head of the fasteners with a hammer ! Don't pound them, just rap them, that should loosen the fastenings in the threads. Use a properly sized Phillips head screw driver, take a pair of vise grips, and gently try to rock/turn the screws loose. Do this lightly, and watch the heads as you do this. If you have jarred the screws enough they should back out. If they don't move try it again, just don't bugger the screw head, hitting it or with the screw driver. If you are not in a rush to get it done, try building a dam with good duct tape and polyethylene plastic to make a pocket. Pour in vinegar to cover screws if possible. Let it sit over night. The vinegar will dissolve the corrosion. You may have to do it a few times, then go back to what I said before, and try again. I did my 53 foot mast and boom, this way which were painted 25 yrs. prior, and only had 1 screw that I could not get out, on my spin pole track. Also a hand held impact driver works well. I stripped my mast with aircraft stripper, then medium blasted it, Then painted by roller, no tipping with Intelux about $300 for the primer, and paint, at home in the yard! The only repair I had was the through hole tubes for the upper, and lower side stays had to be replaced, as they were broken free of the mast, by previous owner, when he tried to remove the thru bolts, which were seized it the tubes. Extremely dumb factory idea, when built!!!!

[Cheechako]

My pro mast rebuild was completely stripped, acid etched, Primered with Chromate, two part urethane painted etc. As I said, it started to corrode in a year offshore.
Nothing better than an impact hammer for frozen fasteners as it does the "hammer rapping" thing mentioned above with each motion. It may come to this for you. However, getting the setting right so it doesn't break right off is tricky.

[Don C L]

Use a zinc-based anti-seizing, anti electrolysis goop. I have also seen a piece of electrical tape between the stainless fitting and aluminum too which seemed to work ok for the contact but not for the threads of course. My 50 year-old fittings on the mast never had anything and now they are welded on. Still holding firm!

[dennismenace111]

Use nylon washers under the stainless screws or bolts. Years ago in worked at Chalks airlines...operating seaplanes to the Bahamas. We fought corrosion constantly operating aluminum airp,anesthesia in salt water.

The only way to prevent galvanic corrosion is to separate the two metals. Nylon washers do the trick.

[chala]

Originally Posted by Don C L

Use a zinc-based anti-seizing, anti electrolysis goop.

I get good result from Duralac.

“Duralac is a chromate containing jointing compound designed to inhibit electrolytic decomposition between dissimilar metals – often called galvanic corrosion. It is a single pack, air setting product. Used correctly, Duralac prevents anodic decomposition.”

By the way, a rope wrapped around an aluminium spare, even anodised, can cause corrosion.

[BigSmile]

I've been experimenting with MasterSeries Silver Paint. I have a test running on a Danforth, and it has been sitting outside for 2 years, and it is still as I have painted it.

It's used in automotive, and marine.

My understanding is it is a urethane with aluminum flake suspended in the urethane. The urethane seals from moisture, and the aluminum flake bonds any oxygen that might try to move thru. Can be applied to aluminum, or steel, but do and cure separately if you ever want the parts to come apart. Can be painted but does not have to be. Can be epoxied, or applied to epoxy that is properly prep'ed. They have a product for metal prep, but can also do with local off the shelf equiv. I have done both.

Give 'em a call if interested, I'm sure you can find the number on the web. They are helpful to talk to, and I'm sure they can tell you more about the marine applications.

[kentobin]

Originally Posted by BigSmile

I've been experimenting with MasterSeries Silver Paint. I have a test running on a Danforth, and it has been sitting outside for 2 years, and it is still as I have painted it.

Interesting paint. When I get around to working on my mast I'll seriously consider it but it's definitely not cheap. Thanks for posting.

MasterSeriesCT Coating Line Rust Prevention - Product Info
MasterSeriesCT Coating Line Rust Prevention - FAQ's
MasterSeriesCT Coating Line Rust Prevention - Prices

[BigSmile]

Originally Posted by kentobin

Interesting paint. When I get around to working on my mast I'll seriously consider it but it's definitely not cheap. Thanks for posting.

MasterSeriesCT Coating Line Rust Prevention - Product Info
MasterSeriesCT Coating Line Rust Prevention - FAQ's
MasterSeriesCT Coating Line Rust Prevention - Prices

They do run specials.

I may at some point here, have a pint I can free up, and send your way to experiment with.

[UNCIVILIZED]

Yep, the metals need to be seperated. You can use Loctite on the fasteners to prevent them from causing corrosion in the aluminum, & it of course secures them in place as well. I'd suggest using Blue Loctite, unless the fastener is to be in a location subject to lots of vibration. As it's Much easier to remove, & unlike with Red, you have a decent chance of extracting the fasteners intact, without breaking them.

For isolating the fittings themselves, most types of thin, durable plastic will work. And if you want some seriously heavy duty stuff, cut your isolators out of 2-liter soda bottles.

Also, while I've not tried it, there are all sorts of polymers & rubber compounds that you can paint onto metal. Which, when they dry, are fairly tough coatings. Some of them are used to coat the handles on (mostly metal) tools, for instance.

Many of the tricks to pull out stuck fasteners have been mentioned. However a few more are;
- Using a penetrating oil or solvent. Including daily, for several days, prior to trying to unscrew things.
- Using heat. Whether from a small torch/large soldering iron. Or some pieces of #10 wire to each terminal of a 12v battery, momentarily.
- Occassionally cold will work. Such as applications of dry ice. Blasts of cold from various penetrating solvents, & concoctions. A long, directed blast from a hose hooked up to a scuba tank. Refrigerants (cringe).
- Sometimes it helps to try to tighten down a stuck fastener, before taking a 2nd try at backing it out.
- Pressure on the fastener's heads while attempting to turn them is another.
- Screaming, Cursing, & Threats of Black Magic, etc.
And a few more that are "trade secrets"


Edit: In a fair number of places, fasteners made from aluminum might work. And in others, things can be attached with Spectra/Dyneema if you get creative.

[topmast]

Has anyone tried painting with Cetol? Blasphemy? Isolate metals as best you can and make it look like wood..No aluminium on my boat but lots of galvi. Worked.