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Old 08-08-2010, 06:27   #1
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Cast Iron Keel

I have a 1200# cast iron bolt on (unencapsulated) fin keel. I would like opinions from people who have refinished similar. After taking down to bare metal what materials and procedures in what order did you use? Primers,paints,fairing and resins. Every thing that needs to be done before antifouling is applied. Thanx for all input on subject.
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Old 08-08-2010, 07:33   #2
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Old 08-08-2010, 14:28   #3
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Thank you for the link Gord. It mentions applying epoxy resin directly over cast iron, I was under the impression that you needed a primer before applying epoxy over cast iron. Also could the primer before antifouling paint be applied in the fall so in the spring all that would be left to do would be put on the antifouling. Comments anyone.
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Old 08-08-2010, 17:54   #4
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cast iron keel - refinishing

Actually, what you have there (iron keel) sucks and should be avoided. But since you already have it (and us here too):

- sandblasting to silver metal (including under the blocks supporting the boat),
- epoxy (epoxy is the primer) - immediately after blasting and wiping with a grease removing solvent (e.g. acetone),
- epoxy,
- epoxy,
- did I say epoxy?
- epoxy,
- fill the surface (epoxy filler),
- epoxy,
- epoxy primer (optional)
- antifoul,

They say it takes the minimum of 8 layers and the layers are best applied at intervals allowing for chemical bonding.

International (among others) makes this kind of epoxy primer. (I believe it may be the Interprotect - but check this out with the dealer.

Pay special attention to the area between the keel and the ballast - it must be dry and the bolts should be tight - if the ballast moves, there will be a crack there as soon as you hoist the boat. Some say it makes sense to slightly glass this area. I believe this is correct since the ballast will move slightly relative to the grp as the boat rolls.

We used Primocon but it was just as good as leaving the keel bare.

I have met one owner who claimed he did his keel with VC Tar. The keel looked pristine.

And if you find THE answer please share it with me!

b.
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Old 09-08-2010, 11:44   #5
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After visiting the Interlux site I am inclined towards the Interprotect 2000e and use the wash/primer for metal before first coat. The 2000e is suitable barrier coat for both metals and fiberglass. I would also use the resin and filler they suggest for fairing. Maybe even use their antifouling, that way everything should be compatible. Anyone have good or bad luck with Interlux products?
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Old 09-08-2010, 13:55   #6
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Blgklr, Epoxy (unthickened) over the freshly raw iron is the best coating you can get. No primer will offer a better bond, in fact priming before epoxy is self defeating and a useless adventure in costly materials. As a matter of fact, the best primers are diluted epoxy formulations!

I takes three coats of epoxy to insure you have a waterproof membrane over the iron. Naturally, you'll want to increase film thickness, but 12 coats is simply ridiculous. Once three coats are down, have a good look at the surface and if major fairing is involved then move onto thickened epoxy and start the fairing and smoothing process.

Now that I've said this, I've been involved in some environmental trials with polyurethane truck bed liner products. These trials have shown to be the only products that rival epoxy (in my testing experiences) in toughness, the ability to stay stuck to submerged surfaces, remain water proof, anti fouling, etc. There are two basic types of this liner material and everyone with big coating issues are now have a good look at these products, such as industrial locations, local and federal governments (bridges, over passes, etc.). the various branches of the military, etc. So, you have options that work and are known to work, or you can fool around with paint company offerings (like the epoxy based Interlux 2000E) which are the very reasons other methods and materials are being explored, as we know paint just doesn't cut it for long.
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Old 09-08-2010, 14:16   #7
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had to renovat my keel on my last boat as well. I would highlight two things:

1. Sandblasting to silver metal as mentioned - forget anything else like brushing or so, only sandblasting works to get ride of most of the rust.
2. Priming right after the blasting is key, and right after means here being closer to minutes than hours No really, each minute the keel is "naked" rust starts to deploy which then will grow under the new coating again.

I found a blasting company which applied zinc right after the blasting (I think its called galvanizing by thermal spraying in English). Ok the keel was off then....
This was very good base for all the upcoming coatings as there was no rust when the keel was coated. I needed much more epoxy coating as the surface was quiet rough but therefore the layer was much thicker. The keel was more or less spotless when I sold the boat two yeas later.

cheers Marco
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Old 09-08-2010, 16:12   #8
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Cast Iron keel

I have a cast iron keel on my Cascade 42. Five years ago I sand blasted it and then applied Two coats of tar epoxy(nasty stuff). As I remember the tar epoxy came from a paint company and was used to coat foundations. Then I applied Two coats of bottom paint over the epoxy. It has held up great.
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Old 09-08-2010, 17:06   #9
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I'll repeat, there is no paint (epoxy based or not) that can compete with unthickened laminating resin (epoxy) over a freshly blasted iron ballast casting.
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Old 09-08-2010, 17:21   #10
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I'll repeat, there is no paint (epoxy based or not) that can compete with unthickened laminating resin (epoxy) over a freshly blasted iron ballast casting.
Laminating resin may or may not be epoxy. Most commonly, it is NOT.
Polyester (Vinylester) resin, for instance, is NOT an appropriate primer/sealer/barrier coat for any material.
Epoxy is.
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Old 09-08-2010, 17:38   #11
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Maybe I should have been clearer . . .
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Old 09-08-2010, 17:52   #12
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Maybe I should have been clearer . . .
Maybe?
You speak with the authority of a pro' - and I am thankfull to be able to expect that level of accurate clarity of you.
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Old 10-08-2010, 01:58   #13
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Being a wise ass is one of my better skill sets, thanks for noticing.
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Old 10-08-2010, 05:44   #14
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Years ago I owned a Shark 24. About 2500+ of these boats were built -- all with iron keels. 25 years ago the conventional wisdom among owners used to be coal tar epoxy as the base coat. I used it and can tell you from experience it was awful stuff, impossible to get it smooth, and if applied too thick it developed runs/sags and that coating would crack over the winter (if too thick) which would lead to rust along the cracks. It would gum up any grinding abrasives in seconds, so I went through a lot of 40-grit and wire disks. There MUST be newer coatings that are better than coal tar epoxy. I have heard of something called POR15 that some people are using.

I think the biggest issue will still be the hull-keel joint.

You should search online for the Shark owners discussion groups -- as there must be a large body of experience out there.

(I would never buy an iron-keeled boat again. It's not a suitable material for the purpose.)
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Old 11-08-2010, 12:52   #15
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Well it seems all epoxys are not the same. Most are formulated for covering cement. But I did find some that specifically mentioned covering metals. A company says to first wash the keel with a 10% phosphoric acid solution and let air dry. Also some said to use primer before covering metal. Found one primer that is called zinc rich. I think to hedge my bet I would go along with the wash and primer. When I do this hopefully the result will last for years.
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