How to resin coat cast iron fin on 36ft yacht

cagey

cagey

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Merry Christmas and a happy new year. Advice or help please. The resin coat that was put on fin probably 20 year’s ago has mostly delaminated, although there are areas where its going to be stubborn to remove, please give me tips how to remove it how to prep the surface, what materials to buy and what weather to avoid, or tell me either what book or website to use,
many thanks
K
 
Ideally, you want to get it really dry, get back to mostly shiny metal with something like a flap disc, treat with some sort of rust converter and coat with epoxy on a hot day.
And do the top and bottom of the keel as well as the sides.
Winter in the We*t Country, you will have to compromise.
Get is as dry as you can and go over the 1st coat of epoxy with a hot air gun to thin it and dry the metal.
I would probably use SP, other flaovurs of epoxy are available.
 
Just finished our keel - cast iron on 42’ 1989 Jeanneau, and in a pretty scabby condition before we started:

Professionally slurry blasted with a medium grit blast medium.

Then working quick, as flash rusting begins immediately, applied the first coat of epoxy (thinned @ about 10-15% to aid penetration into what will likely be a porous ‘pumice’-like surface, at least in places on ours).

You can add temporary corrosion inhibitors to wet blast system, use something like Bilt Hamber’s ‘Atom-Mac’, or use mild dilute phosphoric acid if you cannot coat immediately. It only buys you a day or two max, though...

Then I painted with probably around 4-5 coats total of Jotun Penguard Express ZP (a zinc phosphate epoxy metal primer). I can’t rate the paint system highly enough. It does cure to low temps. On some days it wasn’t ideal and probably saw some humidity/moisture during the cure, although obviously you want it as dry as possible.

But this was all in Oct/Nov (North Wales). I don’t quite but the ‘has to be bone dry’ or ‘no good unless it’s summer’ arguments - but now until, say, March in northern hemisphere probably won’t be any good.
 
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This was after the first couple of coats. Ignore the moisture streaks - the boat had just had a wash!

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The only real problem encountered was 'pin holes' where the paint just wouldn't fill some of the most porous/pumice-like areas on the surface. Thinning it right down and applying with a brush - rather than roller - for one coat did help. I could drill them out individually and fill them with a syringe, but now it's back under lockdown I'll probably just wait until spring when the whole lot needs fairing anyway. Hopefully the zinc phosphate will help inhibit any corrosion if moisture has got to the cast iron through those pinholes.
 
Cagey I am not surprise an epoxy coating has broken down on a cast iron keel. Cast iron is not completely solid, but slightly porous. So, no how well it is prepared before coating it wil breakdwown the bond. My keel was treated at 35 years old by taking all coatings off with a disk sander and treated twice with Fertan rust treatment. This was followed with 5 coats of Internation Primocon primer before antifouling. Everytime Concerto is lifted, there are some small patches of rust on the keel. These are treated with the same treatment. Every time the amount of rust is less than the time before.
 
Epoxy can of course form an excellent bond to cast iron. The original coatings seem to last a good 25+ years! Yes, they were factory applied - but I doubt this was done in ‘paint booth’ conditions.

OTOH, I partly wish I’d gone the vinyl primer route (Vinyguard for me), as it is potentially a lot less work/faff than epoxy.

But as per the above, Primocon etc. will need annual maintenance and suits a yearly haul out/laying up routine. We plan to cruise in areas where this might not always be possible, so are hoping instead that the epoxy will give us a period of ‘maintenance free’ service.

Also if, like ours, the keel is badly pock marked (‘cratered’ more like!) then there’s not much point fairing on top of a vinyl single component primer. So here again, for us, epoxy was the best option.

It’s only a keel though and it ain’t going to rust away, so weigh up the faff against the moisture resistance and longevity of epoxy with that firmly in mind.

To be clear, I highly doubt a keel that’s already rusting could be prepped for epoxy without blasting (so herein lies the faff)... don’t ask me how I know!
 
having a steel boat I have used the technique as described above. I would all that I prefer dry grit blasting to produce a rough surface for the paint to grip.

You could also paint with 2 coats of phosphoric acid with a wash down. I always use epoxy tar below the waterline for the extra protection.

Ensure subsequent coats go on within 24 to 48 hours to ensure proper adhesion to the previous coats.
 
I (and several other boat owners I know) have had some success in building a tent around the keel and putting various fan heaters in to warm and dry the keel. It’s a big thermal mass to warm up though!
However after grit blasting and six or eight coats of epoxy and several coats of coppercoat there’s no rust coming through several years later.
 
cagey said:
Merry Christmas and a happy new year. Advice or help please. The resin coat that was put on fin probably 20 year’s ago has mostly delaminated, although there are areas where its going to be stubborn to remove, please give me tips how to remove it how to prep the surface, what materials to buy and what weather to avoid, or tell me either what book or website to use,
many thanks
K
Click to expand...
Why are you doing it? Its not a big issue. If it bothers you that much, grind back the patches, slap on some primer, then hammerite then antifoul as normal
 
My tuppence: Haul out for a hot week in summer, it's cheaper anyway and everything works better.
Media blasting, rather than angle grinders etc. .
The hotter you can get it, for the longest time, is best due to porosity... mine sweated like a toad doing this in hot summer weather!
Thinned epoxy as above ^^.
 
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