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Old 21-06-2010, 10:47   #1
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Cast Iron Primer for Keel / Hull Joint

I'm recaulking the keel hull joint, I've removed old caulking and cleaned out the joint as well as possible, it's about .25 - .75 of an inch around the flange at the top of the keel with exposed cast iron on the keel side and glass on the boat side

I'm filling the joint with 5200, what should I prime the joint with? I need to treat the iron before I apply 5200 or it will just be stuck to the oxidizing iron right? I was planning on using pettit protect (high build epoxy primer) but it looks so thick that it will fill the joint and I won't get good coverage with the 5200

Should I apply ospho or a converter (crc's comes to mind) or a different type of epoxy primer? Before the 5200

Thanks!
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Old 21-06-2010, 11:06   #2
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Personally, This is what I would do!

I would sandblast the top of the iron keel or whole thing depending on size. paint it with the best marine grade primer for metal I could find, locally.

And for the hull a good sanding with an 80 grit just to prep the whole surface.

Tape off the edges before starting. Using 5200 get a 100% coverage eliminating any air bubbles that you can and mount the two together with the nuts not fully tight, align the keel straight and let cure for a couple days or a week depending on the size.

Then tighten up the nuts the rest of the way.


What boat is this?
Quote:
it's about .25 - .75 of an inch around the flange
It sounds like a 20 -27 foot'r. There could be other things to consider.

Del.............................._/)
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Old 21-06-2010, 11:18   #3
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It's a 37' chris craft apache, I'm not dropping the keel just recaulking the joint -- wondering if I should treat the iron in the joint before 5200 or just caulk immediately after cleaning, the keel has been barrier coated and painted it's the iron in the joint I'm concerned about

Thanks!
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Old 21-06-2010, 11:39   #4
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Originally Posted by brianontheroad View Post
It's a 37' chris craft apache, I'm not dropping the keel just recaulking the joint -- wondering if I should treat the iron in the joint before 5200 or just caulk immediately after cleaning, the keel has been barrier coated and painted it's the iron in the joint I'm concerned about

Thanks!
If your not dropping the keel & cleaning the iron then it will not matter what you do! It'll still need it again in a short while. The iron oxide will grow under the caulking and let loose.

If the keel is real tight you can seal then glass/epoxy over the joint going 4-6" to each side and fair it in.

If it's not tight then you need to drop the keel and stop the movement. If on the hard, one test is to fill the bilge with fresh water and see if it leaks out the seam. If so, then it's time for re-beding!
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Old 21-06-2010, 11:59   #5
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As for classing over the joint -- from what I understand glass doesn't want to stick to iron either and is that glass going to affect the 5200, as in if the glass pulls away from the iron will it pull the sealant out with it? What about using g/flex in the glass would that give it enough flexability?

As for just recaulking the joint and the rust growing underneath the caulking would a primer slow or prevent this, what about a coating or two of epoxy before caulking, or a metal primer like pettit's rustlok? Would that improve the situation some?
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Old 21-06-2010, 23:54   #6
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As for glassing over the joint -- from what I understand glass doesn't want to stick to iron either


what about a coating or two of epoxy before caulking,
Quote:
the keel has been barrier coated
Aren't these contradictions?
If a barrier coat (epoxy/aluminum powder) will stick to iron so will glass/epoxy. As for the 5200, once it's cured, being glassed over will not affect it.
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