Cleaning up a cast iron keel

Jul 7, 2004
8,402
Hunter 30T Cheney, KS
I know there was discussion on this but it doesn't come up on a search. I was looking for the process to clean up the rust bloom on my keel. It looks bad and definitely makes for a rough keel surface. The was some talk on grinding it down to bare metal and resealing it before new bottom paint. I want to get prepared for an early Spring project so I can launch on time.
If someone could just point me to the thread it would be appreciated. Thanks!
 
Oct 30, 2011
542
klidescope 30t norfolk
Yep grind down to bare metal and epoxy seal it using interlux e 2000 paint. Or equivalent. Oxphoris paint works well as a primer before epoxy. And fairing is done over the epoxy with west system then another layer epoxy sealer then bottom paint. If you have just some rusty spots you can just sand and fare each one and not whole keel just make sure you seal steel up good soon after grinding so rust doesn't reappear
 
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Jul 7, 2004
8,402
Hunter 30T Cheney, KS
Thanks! More bloom keeps appearing so I plan on working the whole keel. How bad can it be??
 

Gunni

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Mar 16, 2010
5,937
Beneteau 411 Oceanis Annapolis
WhatFiero describes the process. Study the Interlux technical documents for specifics on underwater steel protection, there are some very important steps that must be followed precisely or you will be back at this job soon. I did my keel last year and there is a lot of bad advice out there on the 'toobs. Your biggest challenge will be staging the work so that you get the bare iron sealed quickly. Even an overnight dew can ruin the job. If I were doing the entire keel I would be tempted to pay a guy to blast it to bare metal then work it by section with wire brush side grinder, sealing with interprotect before moving on to the next section. My approach was to do a new section each year for 3 years while I worked out my approach. Scrubbing regular marine epoxy into a cleaned up rust pock with a wire brush will often give you good temporary results and slow the growth of rust.

Both Interlux and Pettit sell a high solids epoxy barrier paint that reduce the number of coats. You need to end up with a defined film thickness (believe it is 10 mil). That is at least 4 coats of Interprotect 1000. Don't skimp. I used Ospho (phosphoric acid, and dichromate) on the bare iron as an extra precaution against microscopic rust. Interlux does not advise that use, but I have seen no failure on my keel and the stuff converts rust to metal improving the bond surface. Good luck.
 
Jul 7, 2004
8,402
Hunter 30T Cheney, KS
Thanks Gunni ! Sounds like I have my work cut out for me. I work alone, so I may have to use your approach and tackle a section at a time. Cast iron oxidizes quickly. You can see it on brake rotors after one damp night.
 
Jan 19, 2010
12,362
Hobie 16 & Rhodes 22 Skeeter Charleston
I sandblasted a keel once but it was a real PITA. In hind sight I would have been better off to pay someone to blast it for me.
 
Jul 7, 2004
8,402
Hunter 30T Cheney, KS
If it's possible for one person to seal it the same day it is blasted, I may try hire someone as well.
 
Jul 7, 2004
8,402
Hunter 30T Cheney, KS
I think I'd like to stick, no pun intended, to the same brand as the bottom paint I use. This page on Pettit is somewhat confusing. They offer this metal primer for underwater cast iron. It's not called a 'barrier' paint per se. Says it dries fast enough to apply multiple coats in one day. It can be top coated with bottom paint
http://www.pettitpaint.com/fileshare/product_pds/Rustlok.pdf

 
Oct 30, 2011
542
klidescope 30t norfolk
That is an extra step you can use that in leu of osphoris paint but a epoxy barrier coat to 10 mil still needs be installed all the way to and above the stub of fiberglass that iron keel attaches to
 
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Gunni

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Mar 16, 2010
5,937
Beneteau 411 Oceanis Annapolis
For what it is worth, my epoxy primer is Interlux Interprotect and my bottom paint is Pettit Trinidad with a topcoat of Hydrocoat. Proper preparation and application is way more important than brand.
 
Jun 8, 2004
10,024
-na -NA Anywhere USA
As a former dealer who repaired cast iron keels, the first thing was to wire brush or a wheel style brush the area to remove debri and rust till it was cleaned. Any sanding after that and then cleaned with acetone. At that point, I applied a metal primer with zinc chromate. There are many primers out there but the key is zinc chromate. Then a two part expoxy was applied. I found the best and most expensive was Watertite because of the slow curing time, it was the hardest designed for water which worked well and held for years. Due to immediate rusting once the metal was exposed, we did a small section at a time. If it was a new cast iron keel, then the entire unit was coated with zinc chromate. At that point then barrier coats minimum of four layers to six and then antifouling paints. I would suggest talking with the local yards as to the best antifouling paint works well in that area. Hope this helps
 
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NYSail

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Jan 6, 2006
3,048
Beneteau 423 Mt. Sinai, NY
So how was the bottom of the keel done. I would assume have the yard life the boat high enough so you can work under and do all sections not blocked. Then following year have them place blocks in different locations and do rest...... Or I could just hang for a couple of days......
 

Gunni

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Mar 16, 2010
5,937
Beneteau 411 Oceanis Annapolis
Request that the yard block the center of the keel one year, and the ends of the keel the next.
 
Jul 7, 2004
8,402
Hunter 30T Cheney, KS
Thanks for all of the excellent advice! Definitely a job that needs to be planned out well. I have a bulb style keel so I can get to most of it. Hanging on the crane may be in the plan for the area I can't get to.
 
Feb 1, 2010
210
Hunter 33.5 El Dorado Lake, Kansas
You need to check out Por15. I have used it on two boats and they still look good. I did also put Interlux over the Por15 on one boat too.
 

Mikem

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Dec 20, 2009
820
Hunter 466 Bremerton
If the keel has been in salt water a good pressure wash should be done to remove salts. Sand blasting an unwashed keel can drive the salts into the steel and compromise future preservation efforts. Salt water or fresh water the keel should also be completely dry as well prior to preservation.
 
Apr 27, 2010
1,236
Hunter 23 Lake Wallenpaupack
I did my 23 keel with the POR15 system. I was Ok with it, but not overjoyed. I used an angle grinder and grinding wheel plus stiff wire brush wheel to get as close to bare metal as I could (no sand or soda blasting). I then used the POR solutions to clean and "de-rust" the metal, and then the POR15 grey paint. One issue is that one of the solutions (the wash I think) needed hot water, tough to get in a yard. The paint goes on smoothly and covers well, and is one-part. I got a few blisters after one season, and some more after each season (it is about 5 or 6 years now). Most of it adheres, but there are a number of spots around the size of a 50 cent piece where it has bubbled. I suspect the barrier coat approach, though more tedious, may be a better seal. Maybe my prep was bad, but I followed the instructions as closely as I could.
I did not do the bottoms of the wings and bottom edge of keel - way too complicated lacking any sling lift on our lake to raise the boat, and I don't care if that small surface area is rusty - I can't imagine fresh water will eat away much of the massive amount of iron there.
 
Nov 9, 2012
2,500
Oday 192 Lake Nockamixon
Old skool method: remove rust and scale as much as possible. Needle gun, sand blasting, whatever. For pitted, heavily scaled, a wire brush would be an exercise in futility, I should think. Coat with 2 coats of Ospho Phosphoric Acid (available in good hardware stores.) Converts to mostly inert iron phospate coating. Coat with marine formula Coal Tar Epoxy per instructions and recommended # of coats. Fill and fair with epoxy fairing material. Sand. Try not to burn through coating. Recoat with Ospho and CTE in case you have burned through. Then prime and bottom paint. Coal Tar Epoxy is what they use for navigation buoys and such.
 
Jul 7, 2004
8,402
Hunter 30T Cheney, KS
Brian, "coal tar" sounds archaic, like out of the tall ship days. They sell it on Jamestown Distributors though. I learn something all the time here. :thumbup:

"Coal tar epoxy primer is a heavy duty, high build protective coating commonly used industrially on barge hulls and underground tanks. This blend of epoxy resin and coal tar makes excellent protective barrier coating for steel, iron and concrete. The tar additive boosts flex and elongation, and is excellent at sealing out moisture. Black color will transfer, so it is not ideal for frequently handled items. It holds up well in marine environments and withstands saltwater immersion. Polyamide cured and can be applied at high film thickness in one coat. Excellent choice for coating metals to prevent rust and corrosion. Used on metal hulls, any type of trailers, truck beds. Great sealer for metal fuel tanks and non-potable water tanks."
 
Nov 9, 2012
2,500
Oday 192 Lake Nockamixon
Yeah, the method I outline is probably not the smoothest for your hard coating bottom paint racing hull, but then again, if you have a racing boat, you probably aren't going to have a cast iron keel. :D