Aluminum mast corrosion repair

[prof_mariner]

My 1980's vintage Isomat aluminum mast has areas of corrosion where stainless fittings were mounted without isolating the fitting from galvanic corrosion. The damage shown below was caused by eye pads that apparently were intended for reaching struts at some point in the boat's history. I've removed them and wire brushed the bulk of the oxidized aluminum off. My primary goal is to protect this exposed metal from further corrosion and (hopefully) fill the rivet holes to limit water from entering the mast. Here are my options as far as I can tell:

1. Pull the mast, remove all the fittings, prep the aluminum, prime and paint. I really don't want to do this at this point.

2. Do nothing. Although it will be ugly, I understand that aluminum will actually protect itself (as long as there isn't any galvanic activity).

Any other ideas / suggestions?

[Nicholson58]

Originally Posted by prof_mariner

My 1980's vintage Isomat aluminum mast has areas of corrosion where stainless fittings were mounted without isolating the fitting from galvanic corrosion. The damage shown below was caused by eye pads that apparently were intended for reaching struts at some point in the boat's history. I've removed them and wire brushed the bulk of the oxidized aluminum off. My primary goal is to protect this exposed metal from further corrosion and (hopefully) fill the rivet holes to limit water from entering the mast. Here are my options as far as I can tell:

1. Pull the mast, remove all the fittings, prep the aluminum, prime and paint. I really don't want to do this at this point.

2. Do nothing. Although it will be ugly, I understand that aluminum will actually protect itself (as long as there isn't any galvanic activity).

Any other ideas / suggestions?

I used the Chromate primer and re-painted. I used Perfection and painted the entire mast. On a smaller mast, I had a welder heliarc patches on the holes.

[prof_mariner]

Originally Posted by Nicholson58

I used the Chromate primer and re-painted. I used Perfection and painted the entire mast. On a smaller mast, I had a welder heliarc patches on the holes.

Did you etch the aluminum before priming? Did you use any filler on top of the zinc-chromate primer? How long has it been since the repaint and how is it holding up?

I've been advised that you shouldn't weld aluminum extrusions as it will weaken the metal surrounding the weld, so I hadn't considered doing that to fill the holes. I also don't want to pull the mast (at least not now) so I don't think welding is an option.

Here's what I'm considering:

One optioin is to clean/etch (using vinegar), prime (using zinc chromate or other suitable aluminum primer), and adhere (using epoxy) a patch (aluminum sheet cut and formed to shape). I hope to avoid using stainless steel (or other dissimilar metal) if at all possible.

Another option would be similar to above, but forgo the aluminum patch and just do it with a bit of fiberglass and epoxy resin. (Did a quick search and found this article: http://www.jamestowndistributors.com...t.do?docId=542 ).

Comments? Suggestions?

[Roy M]

You guys are a kick in the butt. Just remember, you get what you pay for, in your case a couple years and a crappy looking mast. An option is to do the job in such a manner as it lasts 15-20 years and looks brand new. And if you replace the fasteners, compression posts and electrical wiring, you will actually have a superior product instead of a bargain. Pose this question to Minaret for confirmation. Oh, I forgot, he's a professional and probably has a vested interest in the final product.

[prof_mariner]

Originally Posted by Roy M

You guys are a kick in the butt. Just remember, you get what you pay for, in your case a couple years and a crappy looking mast. An option is to do the job in such a manner as it lasts 15-20 years and looks brand new. And if you replace the fasteners, compression posts and electrical wiring, you will actually have a superior product instead of a bargain. Pose this question to Minaret for confirmation. Oh, I forgot, he's a professional and probably has a vested interest in the final product.

Getting tired of replies like this one. Insulting and condescending, while not contributing to the thread in any substantive way at all.

[Roy M]

Please excuse my candor, "prof_mariner", but in your considered, professional opinion, do you actually expect those of us who actually perform this work to accepts statements such as: "One optioin is to clean/etch (using vinegar), prime (using zinc chromate or other suitable aluminum primer), and adhere (using epoxy) a patch (aluminum sheet cut and formed to shape). I hope to avoid using stainless steel (or other dissimilar metal) if at all possible."

1. Don't screw around with home-grown alternatives to sophisticated products and expect the results to be equivalent.
2. Adhering shaped aluminum sheet (as in beer cans?) with epoxy resin to an aluminum mast? Give us a break.
3. Avoiding dissimilar metals? Have you found a source for super strength 6061 T-6 aluminum fasteners? What would your sail track be composed of (and the fasteners holding it on)?

As a caveat to other readers who might be taking this April First discussion seriously, there's an old phrase I learned from an old salt named Jim Brown, creator of the Searunner trimarans, Constant Camber designs (with John Marples), and the windrider series of sport boats: "Don't use a dime-store pen knife to fix the sore tooth of a tiger".

If you expect to get a good result, use the best materials, use them professionally, and don't take shortcuts because the right ways cost too much and take too much effort. People's lives are at stake when you mess with boats. If the rig fails, or some other mission-critical component doesn't do its job, people and property can get hurt. That's why the FAA won't let handymen repair airplanes.

[Cheechako]

Time to rebuild. IMO. Acid etch the corroded areas. If not too deep you could just acid etch and structural epoxy fill and fair then paint. Weld doublers over those areas and you can remount similar appliances as were there and be better than new. Nicely done doublers can also be structural epoxied and riveted on. Seen complicated racing masts modified in this manner.

[neilpride]

Dont weld, from the pict you have a lot of pitting around, what we can do in this cases in the rigging shop is to fabricate alu pads in diferent sizes and forms, we use ss screws to fit the pad in the corroded area , and between the ss part and the pad we fit a plastic sheet and some tefgel, beware some isomats mast use ss bushings in spreders tangs or forestay , take a look there, its a 1980 isomat spar, if you never see the mast in the ground maybe its a good idea to make a full refit in the spar, beware of electrical wires to, we replace a lagoon 400 mast because a positive wire in a wind generator chafe with the mast and electrolisis trash and compromise the mast itself... painting its another option after the areas are fix it with pads , or if the pitting is not deep , epoxy and primer do the trick....good luck.

[prof_mariner]

Thanks Cheechako and Nicholson58. I do plan on pulling the mast at some point (probably next year) but would like to do whatever prep work I can now while the stick is still in the boat. While searching the net and talking with folks who's opinion I trust, I've been getting lots of conflicting advice: some say paint, others say paint won't work and I'll have to re-anodize; some say weld, others say welding weakens the aluminum; and so on. My hope was to get some feedback from the forum on the subject.

[prof_mariner]

Originally Posted by neilpride

Dont weld, from the pict you have a lot of pitting around, what we can do in this cases in the rigging shop is to fabricate alu pads in diferent sizes and forms, we use ss screws to fit the pad in the corroded area , and between the ss part and the pad we fit a plastic sheet and some tefgel, beware some isomats mast use ss bushings in spreders tangs or forestay , take a look there, its a 1980 isomat spar, if you never see the mast in the ground maybe its a good idea to make a full refit in the spar, beware of electrical wires to, we replace a lagoon 400 mast because a positive wire in a wind generator chafe with the mast and electrolisis trash and compromise the mast itself... painting its another option after the areas are fix it with pads , or if the pitting is not deep , epoxy and primer do the trick....good luck.

Thanks Neil. It's actually a 1986 Isomat spar on a Beneteau F405. I've had a rigger up the mast and he didn't report any issues at the spreader tangs, but I will certainly check this myself as well.

[neilpride]

Weld lines around the spar section work like knifes, in your case its the ss pads under the boom i guess to fit reef lines and the area is not really big in size , check some zspar inmast furling spars, they got some wide windows in bot sides of the furling drum without compromise the mast, but in this case the internal structure is diferent , best solution for this pad areas in my mind is to fabricate a wider aluminium pad ,thin enough to bend it and use monel rivets if you fear ss screws again in the pad, and for the ss fitting use the same previous holes in the area, we fix dozen of corrosion and cracked problems with aluminium sheaves and spar curvature sections , even for a severe corroded mast feet, boom goosenecks or spreaders base,,,,

[Cheechako]

Originally Posted by prof_mariner

Thanks Cheechako and Nicholson58. I do plan on pulling the mast at some point (probably next year) but would like to do whatever prep work I can now while the stick is still in the boat. While searching the net and talking with folks who's opinion I trust, I've been getting lots of conflicting advice:
some say paint, Paint seems to have a limited life on masts but it is the normal way big ones are most often done. You can acid etch and zinc chromate those areas for now. The key is to stop any corrosion. I suppose just a good clean up and leave it bare is ok too. Bare alum masts seem to last very well unles incompatible things are mounted to them. They do get rather dirty... grey oxide coming off on hands and sails.
others say paint won't work and I'll have to re-anodize; Re-Anodizing is likely out... hard to find tanks that big for an aftermarket work and not done perfectly can cause damage due to hot spots on old pieces like that. Maybe you would be lucky and have someone nearby, but not likely.
some say weld, others say welding weakens the aluminum; and so on. Masts have been welded for a long time, many are joined in the middle and welded. Welding on pads to thicken a mounted object can be a good thing.... better than stacking corroding componants. Yes welded aluminum is softer at the weld. All aluminum boats are welded throughout!

My hope was to get some feedback from the forum on the subject.

Those are my ideas.

[prof_mariner]

Originally Posted by neilpride

Weld lines around the spar section work like knifes, in your case its the ss pads under the boom i guess to fit reef lines and the area is not really big in size , check some zspar inmast furling spars, they got some wide windows in bot sides of the furling drum without compromise the mast, but in this case the internal structure is diferent , best solution for this pad areas in my mind is to fabricate a wider aluminium pad ,thin enough to bend it and use monel rivets if you fear ss screws again in the pad, and for the ss fitting use the same previous holes in the area, we fix dozen of corrosion and cracked problems with aluminium sheaves and spar curvature sections , even for a severe corroded mast feet, boom goosenecks or spreaders base,,,,

I'm guessing the eyepads were intended for reaching struts that are no longer on the boat. Whoever installed them didn't put any isolation barrier between stainless steel and aluminum thus causing what you see in the photo.

I would much prefer to use monel rivets, but I've not found a source for them in the US.

[prof_mariner]

Originally Posted by Cheechako

Those are my ideas.

Another very helpful post, thanks very much. Regarding welding, the rigger I spoke to (and he's arguably the best rigger in the area) is the one who cautioned me about welding. I brought up the same argument you posted and he claimed that before pads / spreaders are welded at the factory the extrusion is heated, preventing weakening the surrounding aluminum. There's a welder in town who is an expert on this subject and I hope to get his feedback as well.

[leftbrainstuff]

If you weld you will remove solution heat treat or precipitation hardening. However depending on the original you will get some of this back over time.

It looks as though this corrosion is not in a high stress location so you are probably better off cleaning to bare metal, chromate priming and painting. You can also use a suitable filler for aesthetics. If you want to fillnholes then you can use a suitable rivet but follow good practice to avoid further dissimilar metal corrosion.

You could do all this work in situ.

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