cast iron keel treatment - Page 2 - SailNet Community

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  #11  
Old 02-29-2012
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Lightbulb Here's one method

I used to know a yard owner that would routinely redo rusty iron keels. As others have noted, you Do need to get the corrosion off, and you Do need to protect themetalright away.

My friend used to tell me that the initial and invisible coating of oxide would start reforming within the hour, after the keel was cleaned "bright."

What he did was to immediatley (!) have epoxy at the ready and a low speed angle grinder with a disposable wire brush (or two) attached. He'd be out there in his tyvek suit and then put on the epoxy and Wire Brush it in, hard, into the iron surface.
The brushes would remove that new layer of corrosion and seal in the new epoxy layer in one step.
Once that was done and cured, would come the fairing and bottom painting.

Like sand blasting, grinding, or sanding, it's not any fun, but it Works.


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Last edited by olson34; 02-29-2012 at 05:40 PM.
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If it is cast iron, I would be inclined just to paint it.

Cast iron is remarkably stable against corrosion.

It corrodes very evenly, and very slowly indeed.
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Quote:
Originally Posted by Rockter View Post
If it is cast iron, I would be inclined just to paint it.

Cast iron is remarkably stable against corrosion.

It corrodes very evenly, and very slowly indeed.
All due respect Rock - I have to question if you have ever SEEN an old iron keel that has not been cared for or protected.

Corrodes evenly and slowly? Maybe in a lab or in theory. In reality they corrode VERY unevenly, they get rough and downright lumpy. Slowly, maybe but only because of the large mass of iron.
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Originally Posted by kjones View Post
.... and 350 for labor. ...
I'm leaning towards having the marina do it just to avoid messing it up my self and having it done right the first time.
My concern is whether the yard will do the job so the result has a shot at being close to permanent. I would doubt that for $350 they will do five coats with fairing, and sanding of any highs as needed. I would do it myself because I am more confident that I would take the time to do the job thoroughly, which you may not get for $350...
Again this is a job that needs to be done correctly, or you'll face doing it again in two years.
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most boats that have iron keels are 25-30-years old and most are still fine if you disturb the natural barrier that has formed it will hasen the oxidation process
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If you get it blasted make sure it is done on a warm dry day and the epoxy goes on within 30 minutes.

I would use a zinc rich epoxy primer and for the first two coats and hi build after that.

If you sand it make sure you wet sand /and / or wear a GOOD face mask. Epoxy dust can land you in hospital.
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most boats that have iron keels are 25-30-years old and most are still fine if you disturb the natural barrier that has formed it will hasen the oxidation process
An untreated iron keel will be so rough it'll take a knot of speed off a sailboat. Combine it with a fixed blade prop and the boat will take on a pretty sluggish attitude. Most sailboats are slow enough when sailing optimally anyway, dragging the equivalent of an anchor behind you, would be well, a drag.
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An untreated iron keel will be so rough it'll take a knot of speed off a sailboat. Combine it with a fixed blade prop and the boat will take on a pretty sluggish attitude. Most sailboats are slow enough when sailing optimally anyway, dragging the equivalent of an anchor behind you, would be well, a drag.
Further, the rust will not stabilize.. I had an iron keel that had been left untreated prior to purchase and I had an inch deep divot 6-8 inches across where rust had gotten a hold of things.

Besides that properly sealing an iron keel will prevent perennial rust stains, weeping and swelling that goes with rust formation. Subsequent haulouts will be much less labour intensive.
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I did it the hard way on my rusty iron keel with a grinder; very dirty job and it rusted up before I finished the other side of the keel. You will likely still have rust left over and lots of pitting.

I used Pettit Metal Primer with Activator to bond to the keel and leftover rust I could not remove. I than applied two coats of Interlux 2000 (read the directions carefully for timing with the metal primer) than applied fairing compound. After fairing the keel, another 4 coats of Interlux 2000 than bottom paint. Keel still looks good 2 years later.

Once you have done it, you never want to do it again. I would spend the $500 for the soda blasting and have them finish by noon so that I had time for one or two coats of paint that day.

Good luck,
george
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Haven't dealt with cast iron, but had a steel centerboard for 16 years. When I bought the boat the original owner had coated it with Rustoleum and--not knowing any better--I pt bottom paint on and launched it for the season.

What a mess when I hauled for the winter! The Rustoleum failed, taking the bottom paint with it. The centerboard was exposed and further pitted all over.

The only thing that worked was having the board sandblasted and coating it immediately. The best treatment, when it became available, was Interlux 2000. I put it directly on the clean metal and built it up with several coats. It only failed where it got dinged when I had been "sailing by braille" in shallow water.

Subsequently, I have used a SS wire brush wheel on aluminum that was below the waterline. I just couldn't get to clean metal in the pits. I applied 2000 after using a zinc chromate primer and it held where there was no pitting.

The lesson learned: forget scraping and brushing. The only was to get to clean metal was sand blasting. I doubt soda blasting is aggressive enough to get all of the pits. Once you get to clean metal, IMMEDIATELY coat it. Zinc Chromate primer (thin coat) on aluminum, followed by 2000. Use 2000 directly on bare (shiny) iron or steel.
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