I have some minor corrosion at the base of my Catalina 30's aluminum mast and I want to take care of it before it gets any worse. I've checked the catalogs and am a bit confused about which metal primer might be best for this purpose. Any suggestions? Would I do well to seal the area after priming with epoxy, or paint, or both? Mike Turner S/Y Amity Long Beach, CA
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Bob Howie
An aviation fix is in order
I have an aviation background, ergo, my recommedation for a fix. Aircraft, for the most part, are built of alloys of aluminum and, as such, all share a grand propensity for corrosion, which, in aviation, is a very, very bad thing. The way the problem is solved in aviation is to acid etch the affected area which removes all the corrosion and then use a product known as Alodine on it. Once treated, corrosion very most likely will never occur in the area again because the Alodine treats the metal at the molecular level. If you are dealing with a painted mast, make sure you have neutralized the area well, mask off you deck and anything else you don't wish to have overspray upon, and use either the yellow or green zinc chromate primer prior to your finish coat. Aircraft mechanics tend to be a friendly bunch and might give you a little advice and some Alodine to complete your project. Just pop into your local airport, ask around and they'll most likely fix you right up. Good luck.
I have an aviation background, ergo, my recommedation for a fix. Aircraft, for the most part, are built of alloys of aluminum and, as such, all share a grand propensity for corrosion, which, in aviation, is a very, very bad thing. The way the problem is solved in aviation is to acid etch the affected area which removes all the corrosion and then use a product known as Alodine on it. Once treated, corrosion very most likely will never occur in the area again because the Alodine treats the metal at the molecular level. If you are dealing with a painted mast, make sure you have neutralized the area well, mask off you deck and anything else you don't wish to have overspray upon, and use either the yellow or green zinc chromate primer prior to your finish coat. Aircraft mechanics tend to be a friendly bunch and might give you a little advice and some Alodine to complete your project. Just pop into your local airport, ask around and they'll most likely fix you right up. Good luck.
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Jack Tyler
If it doesn't fly...
Hi, Mike - bet you have your boat in the HUGE marina in our former hometown. As a fellow pilot, I think Bob's advice is just fine. Except it may not last. It's a sad, hidden fact in recreational boating that aluminum is a very hard metal to keep hidden from sea water. The best answer is to irridite and then anodize it. That's not practical in your situation. On what is your mast stepped (on deck)? If it sits on top of a stainless pad or plate, that in itself is a huge problem (dissimilar metals). Usually, that's the case since a spar can't just be placed on top of relatively soft fiberglass. Even if the plate is also aluminum, it may be of a different enough alloy to spawn an electrolysis problem. Try Bob's approach and see if it arrests corrosion over the long term. If it doesn't, consider using an inert base (Starboard is often used for this) on which to step the mast. When this kind of retrofit is done, the spar is often cut by the dimension of the new step - that way, the rig remains as before. Jack
Hi, Mike - bet you have your boat in the HUGE marina in our former hometown. As a fellow pilot, I think Bob's advice is just fine. Except it may not last. It's a sad, hidden fact in recreational boating that aluminum is a very hard metal to keep hidden from sea water. The best answer is to irridite and then anodize it. That's not practical in your situation. On what is your mast stepped (on deck)? If it sits on top of a stainless pad or plate, that in itself is a huge problem (dissimilar metals). Usually, that's the case since a spar can't just be placed on top of relatively soft fiberglass. Even if the plate is also aluminum, it may be of a different enough alloy to spawn an electrolysis problem. Try Bob's approach and see if it arrests corrosion over the long term. If it doesn't, consider using an inert base (Starboard is often used for this) on which to step the mast. When this kind of retrofit is done, the spar is often cut by the dimension of the new step - that way, the rig remains as before. Jack
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Bob Howie
Permanent fixes...no promises
Jack is right about the unlikelihood of anything near a permanent fix and his suggestion about upon what is the mast stepped is good, but i've never heard of starboard being used. If there is no compressibility factor, certainly that stuff is worthy of use. And, he might be right about electrolysis having something to do with the corrosion at the bottom. As far as any permanentcy is concerned, I had some light surface corrosion on my boom four years ago, took the boom off, removed all the fittings, dropped the boom in an acid tank I built in the shop and the alodined it inside and out. No problems since. Spar makers also tell me that most of the corrosion that takes place with a mast is more external than internal. And, my spars are not painted. Just a bit more info I thought of after reading Jack's.
Jack is right about the unlikelihood of anything near a permanent fix and his suggestion about upon what is the mast stepped is good, but i've never heard of starboard being used. If there is no compressibility factor, certainly that stuff is worthy of use. And, he might be right about electrolysis having something to do with the corrosion at the bottom. As far as any permanentcy is concerned, I had some light surface corrosion on my boom four years ago, took the boom off, removed all the fittings, dropped the boom in an acid tank I built in the shop and the alodined it inside and out. No problems since. Spar makers also tell me that most of the corrosion that takes place with a mast is more external than internal. And, my spars are not painted. Just a bit more info I thought of after reading Jack's.
Assume that your mast is painted?
Mike: I must assume that you mast is painted? We have boats in our marina (fresh water) that have painted masts and show the same signs as yours. These boats have been in salt water at sometimes during their life time too. I would have to agree with you that you want to clean it up, but would have to agree with Bob that this is probably a cosmetic thing.
Mike: I must assume that you mast is painted? We have boats in our marina (fresh water) that have painted masts and show the same signs as yours. These boats have been in salt water at sometimes during their life time too. I would have to agree with you that you want to clean it up, but would have to agree with Bob that this is probably a cosmetic thing.
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David
Mast
If I am not mistaken your mast is keel stepped and could be suffering from electrolytic corrosion (not electrolysis). I would suggest you have it inspected by a professional rigger before following any of the previous responses.
If I am not mistaken your mast is keel stepped and could be suffering from electrolytic corrosion (not electrolysis). I would suggest you have it inspected by a professional rigger before following any of the previous responses.
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