What to do about a cast iron Keel?

[marlin]

Since I have had 93 of you folks read my previous post and nobody replied, I thought I'd start over with a new thread title:)

Am I the only one whose keel is rusting away?
I own an oldie but good SO 44, circa 1990. I bought the boat in 1996 and out of necessity I had the keel sand blasted and epoxy coated in 1997. In 10 years 75% of the epoxy has been replaced by rusting cast iron.

I need a keel coating solution that will last. I am looking for brands that you have had success with. Epoxy or other coatings and methods. Any input from this vast audience of experts will be appreciated.
Thanks!!!
Marlin
~~~_/)~~~

[MalcolmP]

Hi Martin

I have not any direct knowledge, but I understand that keel corrosion may also be a result of electrolysis, so when you get your keel retreated ensure that it is also bonded back to a suitable anode system

Malcolm

[mathias]

Hello Marlin,

It took some time to answer but first I had to translate from German to English.
Now, here you can read about my way to refit keels consisting of cast iron or steel. I don’t know where are you live in…so possibly you can`t receive some of the products which are given below.

1. To remove old coatings by portable grinder or wet grinding.

2. Machining iron surface with wire brush on angle grinder. There shouldn`t be any paint or loose rust but there is no need to keep surface like a mirror. Working with PERAGO discs might be successful, too (https://www.svb.de/cgi-bin/svb.pl?uid=1106255u116599877621224319061&make=lge&lge=_en&res=high).
Don`t damage the GRP-hull at the interface to the keel.

3. To clean, to dry and to degrease iron surface.

4. Applicate BOB-Rustsealing (1x) with brush (https://www.svb.de/html/Grundierungen-DiverseHersteller.html).

5. Stopping with epoxy filler (don`t use polyester filler!) and sanding the surface.

6. Applicate BOB-Rustsealing (1x) with brush.

7. Applicate HEMPEL LIGHT-PRIMER (2x) two-component epoxy primer.

8. Kindly wet grinding by using granulation 240, cleaning surface and to dry.

9. Applicate two-component thick-film epoxy to the surface. Depending on the favoured product there are up to seven coats required, minimum five coats. (INTERNATIONAL: VC-TAR2, GELSHIELD 200. HEMPEL: HIGH-PROTECT. CTM: SP-PROTECTA...there are some more suppliers).
If you are working in accordance to the overcoating times there won`t be any need of sanding between the coats.

10. Kindly wet grinding (granulation 600) to prepare coating of antifouling.

11. To applicate antifouling.

It would be advantageously to jack up the hull so the keel is freely suspended….perhaps your boat is too big….

Finally it is a lot of work. I did it two times (at different boats) and everytime there was a good result.


Greetings from the Lake Constance / Germany,

Mathias

[rogersailor]

We have a similar problem on our Jeanneau 45' near Vancouver, BC/Seattle. Looking at grinding, coating with DEOX C gel, then 2 part epoxy before antifouling. Advice welcome!

[sitara]

An old boat of mine had a badly rusted keel and I was told to clean it up and paint it with a 2 part epoxy. This only lasted a season before it was coming off again. So a second try, grinding down to clean metal but this time using a tar epoxy paint as the first layer. It was black, messy and dried to a rubbery feel. Then two coats of white 2 part epoxy and then antifoul. Ten years later the keel was still fine.

My recommendation is find a good brand of paint and follow their instructions to the letter for preparing and painting cast iron. In my case I used Norglass paint. Good luck.

[Don Reaves]

I had my iron keel sandblasted, faired, and recoated with epoxy barrier coat and anti-fouling. In my case, the rust was not very bad, only in small spots. Apparently, the original barrier coat was not applied properly, and it tended to flake off. In the five years since the repair, the keel looks like new.

[vasko]

My keel looks good from rust point of view but really a lot of barnacles always - huge difference between hull and keel

[cayoloco]

My 2005 43DS came with it's own handful of rusty keel issues too.  Sailing in the Great Lakes is obviously less corrosive than salt water, but the iron keel will still rust.  When I attacked my keel 2 years ago, the first thing was to strip all the bottom paint off the keel, leaving only the epoxy barrier coat.

I then ground every rust spot with a hand grinder with a 60 grit wheel and feathered the bare metal into the remaining barrier coat.  Important; once the rusted spot was complete clean and bare, I immediately applied a West Systems G-Flex epoxy (with no fillers) directly to the exposed metal just to seal the metal, then moved on to the next rust spot. Once all the rust spots were ground faired and coated, including under the keel, I fared to ground spots with West Systems G-Flex epoxy with micro-balloon filler to thicken it.  G-Flex is your best epoxy for coating metal because it's designed to be tough and flexible, so expansion and contractions of the keel in hot and cold weather wont crack the epoxy. 

After filling, fairing and sanding the entire keel with 150 grit, I applied 6 coats of Interlux Inter Protect 2000E.  The first 3 coats were blue and the last 3 coats were white.  The color is important because as you sand and fair, you need to know when to stop and the color of the first barrier coat gives you and indication that you've gone too far.  Following the epoxy coating, I long boarded the keel smooth to 400 grit.  Once the finish sanding was complete, I used VC17 bottom coat, and the keel has never rusted since.  Give it a try.

[johannes]

I second what others have indicated: don't leave the exposed iron surface long before treating it. Ideally not more than a few hours. Also be careful with the temperature. It can take a long time for the metal to warm up after a cold night.

[jdl01]

I have found that with any barrier coat or epoxy on iron keels, achieving longevity of the finish requires immediate treatment of any rust blossoms that may appear from dings or failed original application. Catch it before it spreads is the best motto. I hoist usually twice a year and always make sure I have some booking time leeway so that I can keep the boat up to dry it out and work on it if necessary. Beyond about a dozen years, you will have to do a major sandblast and start over with a complete fresh iron surface.

[geitz]

Nov 7, 2019 14:20:27 GMT johannes said:

I second what others have indicated: don't leave the exposed iron surface long before treating it. Ideally not more than a few hours. Also be careful with the temperature. It can take a long time for the metal to warm up after a cold night.

You can treat the exposed iron with Ospho - ospho.com/

It converts iron oxide into iron phosphate, which is a rust retardant. Once it dries, you'll have time to apply primer without worry of rusting in the meantime.

[MartyB]

I did this two years ago. There is also a galvanized coating by Petit that you can put on the keel before the epoxy coast that will help seal and keep the rust out too. IIRC I had about 40 hours into redoing my keel. Granted I was doing my self, probably not as quick as a pro........

Unfortunately, this is a pretty common issue. Any of the local boat yards here in the Salish Sea have done 1 or 2+ dozen iron keel restorations. You will need to do every 10-15 years or so, depending upon how good the last person was doing things, how many times you remove barnacles fom the bottom of your keel in the shoal spots locally....lets not forget the floating wood debris that make thee way under the boat etc.

Marty

[zaphod]

Nov 7, 2019 19:41:24 GMT jdl01 said:

I have found that with any barrier coat or epoxy on iron keels, achieving longevity of the finish requires immediate treatment of any rust blossoms that may appear from dings or failed original application. Catch it before it spreads is the best motto. I hoist usually twice a year and always make sure I have some booking time leeway so that I can keep the boat up to dry it out and work on it if necessary. Beyond about a dozen years, you will have to do a major sandblast and start over with a complete fresh iron surface.

That's pretty much the same advice I was given. I've never had an iron keel before, and when we had Azura out of the water for the purchase survey, the surveyor pointed out a couple of small rust spots and told me it was not a big deal as long as you stay on top of it. He warned me DO NOT ignore the small spots or they will grow. I am guessing that spot rust repairs will become part of my haul out routine. I just had a few spots repaired while the boat was out last week. We will see how long it takes for more to appear.

[jdl01]

A rough guide to spot repairs is to grind back to metal an area approx. two inches beyond the rust blossom as water may have penetrated this far but has yet to appear as oxidation - rust.

[so40gtb]

I have fought "keel rash" on our prior SO34.2 and current SO40, though, being Great Lakes boats, they are not exposed to the worst corrosion conditions. The key thing is to be aggressive in eliminating it each season, inspecting thoroughly for any rust spots and repairing them immediately (or, in our case, as soon as the snow stops and it's not too cold in the boatyard). I grind out the rust spot, plus an area around 15 mm outside it, remove residue with (take your choice of environmentally unfriendly solvents), apply Interlux 2000 epoxy barrier coat, and then the normal annual bottom paint. The more careful and aggressive you are, the less problems you will find next year. In my experience, electrolysis has a greater impact on areas around parts attached to the shore power "earth" protective ground, such as the prop shaft, skeg, etc. and really doesn't impact rusting of the cast iron keels.

--Karl