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Old 14-01-2015, 16:21   #1
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Mast corrosion

I am needing advice on how to proceed. My main mast has heavy
corrosion from the base up about 2". What are your suggestion on repair? The shoe is not pitted, keel stepped and mast hight is about 62'. The rest of the mast is in good shape.
Thanks for the great advice in advance.
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Old 14-01-2015, 16:46   #2
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Re: Mast corrosion

A sleeve do the trick, now the point if is external or internal, you need to measure the gap around the mast base in contact with the mast step, if there is few mm around to fit a external sleeve , good, if not you need to make one internal , i guess is a keel stepped mast , clean that corrosión with acid and wire brush before do any job in the mast,,, all depend of the mast step form,,, if you post a pic from the step i give you a real solution real quick.... Cheers....
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Old 14-01-2015, 17:12   #3
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Re: Mast corrosion

and look at what it's sitting on... steel? ie: why is it corroding so much? May just be nature of the beast.
Also, depending on the situation, you might be able to cut it back a couple inches and add a spacer/isolator to make up the 2". This might keep it out of the water so much also.


Whatever you do I would clean it up well and paint it thoroughly for the last foot or so...
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Old 14-01-2015, 17:21   #4
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Re: Mast corrosion

take a look at replacing the mast step .. that might be enough.
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Old 14-01-2015, 17:28   #5
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Re: Mast corrosion

Lol! cutting a mast is serious bussines , we dont even try that no matter what, if you fail to follow a perfect line around the mast you can end in a nightmare, the mast need to rest in the step even, all the sides touching the step with no higs or lows around, if you let the mast rest uneven in the step you can créate a hig load spot and break or crack the mast base in short order, cutting the corroded área sounds ok in theory but believe me, is really hard to créate a flat base again,,,
Just saying!
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Old 14-01-2015, 17:39   #6
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Re: Mast corrosion

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Originally Posted by Cheechako View Post
Whatever you do I would clean it up well and paint it thoroughly for the last foot or so...
Zinc chromate primer is the stuff. Apply to the base and the mast bottom. Just don't breathe it in!
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Old 14-01-2015, 19:04   #7
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Re: Mast corrosion

I had corrosion like that on the seal area of a deck hatch for my lazzarete. The advice from the materials engineering folks was to use an alodyning solution for surface conversion of the bare aluminum. But first, you have to get the corrosion material off, all of that white stuff including down in the pitted area. You have to go to the bare metal. If you miss some of the white stuff, you may have to do it again in a few years (I have had that experience). What works good for removing the white corrosion product is a Dremel tool with a small rounded steel burr bit, plus a reasonable amount of patience. You can get into pretty small pits with that. You then put on the alodyning solution, a rather nasty phosphoric acid. Use googles and gloves. It comes as a powder. You mix it with a bit of water, and you don't need very much. After a bit, the aluminum turns to a gold-orange color, and then you can rinse the acid off with fresh water. After the aluminum drys for a day or so, then you can fill in the pits with an epoxy. JB Weld works pretty good for that, but don't use to much or you will spend a lot of time sanding it smooth. McMaster Carr (mail order, on internet) has good prices on JB Weld epoxy kits. They may have alodyning kits; not sure. I got mine from Smith & Co, the folks that make the epoxy glues and sealers. They are in Richmond, CA, and you can order factory direct.
If you have those chemicals, and the Dremel with the burr bit, you will be in business. Also get some baking soda to neutralize the left-over acid solution. It takes a surprising amount.
However, all the other precautions that have been mentioned still apply.
billr
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Old 14-01-2015, 19:08   #8
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Re: Mast corrosion

Thanks so much. The interior of the mast is good, I wanted to know if you thought it was better to cut the mast off by 2" or do a strap. I think you agree the cutting is a not. Next question, should I weld the strap or can I rivit the strap around the mast.
Someone ask about the step? I am not sure about the composition, but the mizzen has a cast aluminum step, I asume the main is of the same composition.
Again, Thanks!
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Old 14-01-2015, 20:17   #9
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Re: Mast corrosion

Quote:
Originally Posted by gwanthon View Post
Thanks so much. The interior of the mast is good, I wanted to know if you thought it was better to cut the mast off by 2" or do a strap. I think you agree the cutting is a not. Next question, should I weld the strap or can I rivit the strap around the mast.
Someone ask about the step? I am not sure about the composition, but the mizzen has a cast aluminum step, I asume the main is of the same composition.
Again, Thanks!
If you use rivets, you need to be sure they dont touch or wear inside of the mast step, if the step is kind of aluminium plate surrounding the exterior of the mast base then fine, use rivets, if the step have a internal collar to keep the base of the mast in place the rivets can touch the collar when you step the mast, in that case is better screws with the right lenght, flush with the interior Wall section...the strap need to be really flush at the bottom even with the mast base .. Good luck.


Welding is a bad idea in a mast...
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Old 14-01-2015, 20:31   #10
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Re: Mast corrosion

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Originally Posted by billr View Post
I had corrosion like that on the seal area of a deck hatch for my lazzarete. The advice from the materials engineering folks was to use an alodyning solution for surface conversion of the bare aluminum. But first, you have to get the corrosion material off, all of that white stuff including down in the pitted area. You have to go to the bare metal. If you miss some of the white stuff, you may have to do it again in a few years (I have had that experience). What works good for removing the white corrosion product is a Dremel tool with a small rounded steel burr bit, plus a reasonable amount of patience. You can get into pretty small pits with that. You then put on the alodyning solution, a rather nasty phosphoric acid. Use googles and gloves. It comes as a powder. You mix it with a bit of water, and you don't need very much. After a bit, the aluminum turns to a gold-orange color, and then you can rinse the acid off with fresh water. After the aluminum drys for a day or so, then you can fill in the pits with an epoxy. JB Weld works pretty good for that, but don't use to much or you will spend a lot of time sanding it smooth. McMaster Carr (mail order, on internet) has good prices on JB Weld epoxy kits. They may have alodyning kits; not sure. I got mine from Smith & Co, the folks that make the epoxy glues and sealers. They are in Richmond, CA, and you can order factory direct.
If you have those chemicals, and the Dremel with the burr bit, you will be in business. Also get some baking soda to neutralize the left-over acid solution. It takes a surprising amount.
However, all the other precautions that have been mentioned still apply.
billr
Billr told me about this thread. I’m Steve Smith from Smith & co. I would add a few things:

The Alodine and a corrosion-inhibiting epoxy primer is what all the aircraft manufacturers use on aluminum airframe parts, both military and commercial (We handle that also). When you see some interior part of an airplane painted yellow-green, that’s the color of that particular corrosion-inhibiting epoxy primer. Btw, it’s based on strontium chromate, not zinc chromate. And speaking of which, billr’s memory has drifted…the Alodine is made with chromic acid, not phosphoric (even more nasty). The Alodine grows a chromate-complex on the aluminum surface that strongly bonds to the aluminum and forms a first-layer corrosion-inhibitor. At the same time, because that inorganic aluminum-chromate complex is grown out of the metal, is strongly bonded TO the metal, it functions also as an adhesion-promoting primer for an epoxy topcoat, which is what you should do, in total, on that aluminum mast and aluminum step.

I am concerned about the unseen inside of the mast. The hollow mast as I understand it is sitting fully on the step with no way to peer inside, but likely has the same corrosion issues going internally as externally.

Mast stepped on keel means it is in the bilge and we all know what’s down there…usually the unspeakable. A proper corrosion-inhibiting coating system is really mandatory.

Steve Smith
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Old 14-01-2015, 21:38   #11
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Re: Mast corrosion

What brand of boat? I had the same problem but much worse on my Pearson. The cause was the steel mast step used by the builder. Have seen a number of mid eighties Pearsons with the problem

I cut 3" off the base of the mast and built a new mast step 3" higher and NOT from steel. With reasonable care you can get a very flat, level cut. When done check it with an accurate square and a flat surface and sand/grind down any high spots.
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Old 15-01-2015, 05:19   #12
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Re: Mast corrosion

Greetings and welcome aboard the CF, Steve S.
Thanks for sharing your expertise!
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Old 15-01-2015, 05:54   #13
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Re: Mast corrosion

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Originally Posted by skipmac View Post
I cut 3" off the base of the mast and built a new mast step 3" higher and NOT from steel. With reasonable care you can get a very flat, level cut. When done check it with an accurate square and a flat surface and sand/grind down any high spots.
Ditto! You can locate high spots with a sheet of sand paper glued to a flat block. Lapping.

I cut 1/2" off my mast the last time it was out. But I added a new cast mast step which was 5/16" higher then the old one. As well a I added a G10 shim to bring it back to specs and isolate the alum from the SS base plate. Check out my blog below.

If you wrap a piece of wide shim stock around where you want to cut, that will create a perfect guide to scribe a line around to cut along and file to finish if need be.



You could add a decorative base plate, the same length as you cut off, under the step, made of a water resistant material, which would also get it out of the bilge and slowdown the erosion process dramatically. You just need to create a flow path for the water to run into the bilge again.

Also, paint inside and out as a secondary preventive. And ditto on the aircraft paints if you want to go to that much trouble. My original base lasted 15 years before I got to it.
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Old 15-01-2015, 19:03   #14
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Re: Mast corrosion

Gerald,
Once you get in their with the dremel tool, you will find out how much damage you have to fix. If you have some really big holes, you may have to do a trim. Hopefully that is not the case. If you use the Alodine solution, let it sit for a while and then GENTLY flush the excess acid off. As Steve Smith once noted, the resulting gold conversion coating is pretty soft when it is forming, and doesn't come up to strength until after it has time to dry. So you don't want to accidently blow it off with a blast from the hose.
Bill
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Old 15-01-2015, 19:32   #15
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Re: Mast corrosion

I want to thank everyone for your input. So much knowledge, so little time for me to think! Everyone is spot on, now I have to decide "what to do".
Just as after thought, I watch the forum every day. Most days I just "say ya, ya someone is spouting BS about something". But I ask a basic question and all the "real sailors" responded immediately with "real solutions". Thank You!
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