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Old 10-06-2006, 11:26   #1
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How to "seal" a cast iron keel?

What's the best, quick way to do this? Let's say you have a cast iron keel that has some bare spots that have rusted.

Best equipment to use to get down to bare metal?

Best way to seal it before bottom paint?

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Old 10-06-2006, 14:28   #2
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Hmmmm, three words that you can only ever use two of at anyone time.


Want it cheap and quick =No good
Want it good and cheap =No Quick
Want it quick and Good =No cheap

Anyway, there is no easy solution to this. Unless you know what is on there as a barrier now, You can't do a patch job. You need to strip the coating off and start a fresh. Sand blasting to a bare metal is your best approach and then use an Epoxy undercoat as a barrier. You are best to follow a recomendation of a recognised brand name.
If you think an epoxy maybe on there now and the good area's look very sound, then spot grinding with a "Flap" type disc is best. But you need to ensure all rust is gone, or has been treated before you apply the barrier coat.
Do NOT dry sand any anti-foul paint. The dust is highly toxic.
Hope this helps


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Old 10-06-2006, 16:35   #3
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I don't know the author, but I saved the article for future use.

"UPDATE 6/13/03
NOTE: Click on shots at right for full view

Now for the dreaded sanding of iron keel, surely the bane of any iron keel owner's existence. Sandblasting to bare iron with a commercial blaster is the best option here. Heavy duty sandblasters usually rent for $100 for a half day, with serious compressor, blaster, and sand bucket. This is easily enough time to do the job although I would recommend preparing the area before you pick it up. Make sure you coat the underside of hull around keel with some rubber backing to keep sand from damaging hull. I actually opted to use a industrial wire wheel brush on a grinder. This actually did ok but one should ultimately go the sand blasting for more perfection. Surprisingly enough, the industrial wire brush did VERY well. IT lasted JUST long enough! One good trick here is to get a leaf blower and focus it on the keel like the pic at right. This blows all the refuse and dust away from the work area. IT helps if you have the boat in a friend's backyard!

Step 2 I have now done the first two coats of POR-15 with good results. One should follow the instructions closely, however. But application of the product is a breeze; it goes on with excellent coverage! I have over 3/4 of my quart left with two coats on the keel above. Pictures will be posted soon. I believe I might bypass the Interlux Interprotect 2000/2001E Epoxy coating as I am not sure it's even now necessary. The covering looks impressive, indeed! I do need to do some fairing and will probably use West Systems Epoxy with #407 as a filler.

Step 3 Well, I have finally faired the keel with West Systems 105 Epoxy with 206 slow hardener mixed with #407 Low Density filler. West Systems products work great and I recommend them just like everyone else. I had to make sure the POR-15 covering, which is shiny and hard as the proverbial rock, was sanded enough for the epoxy to make a good bond. I used 80-100 grit for this.

Ultimately, this is the step where time does help as you really need several steps of fairing to get the keel perfect. You can get as particular as you want but if not racing, common sense rules. However, the more careful you are in this step, the better the results will be. One careful fairing run will do better than two sloppy ones. OF course, a lot of the final result is the sanding, which is surely MUCH easier if you are smooth with the fairing step.

I had purchased Interlux 2000/2001E as my barrier coating paint after the fairing. I think this will be taken back since two more coats of POR-15 would seem just as fine a choice based on results so far. This stuff really does well and had gotten nothing but high marks from others who have used it. "

Author unknown


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Excellence, therefore, is not an act but a habit."
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Old 10-06-2006, 17:36   #4
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Thanks, Alan and Jentine. That POR stuff looks like the way to go.

Since I am in New England and have already missed about 20% of the sailing season, I am going to do a quick patch-type job for now. Then in the fall if necessary do the full sand-blast route.

That will motivate me to find a winter lay up yard that will accomodate the sand blasting.

I want to make sure I can get to the bottom of the keel for the full job. Can yards typically help me to do that on a 15,000 pound boat, without tying up a travel lift?
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Old 04-04-2007, 19:11   #5
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The simple and correct answer is don't encapsulate

instead grind the iron keel down to grey metal and apply one or twocoatings of Pettit Rust Lok also sold as Trailer Kote or Coat but in Europe they use the name Screwfix. This product bonds with the metal and then expands or contracts with temperature changes. Regular paint will flake off and encapsulating seems to always end up with separation as the water finds away at some point or another (unfinished edges or scuffed bottom from groundings usually) and if the metal wasn't thoroughly cleaned from continued rusting which expands and breaks paint or encapsulation. None of that occurs with Rust Lok.

Michael D.

PS I'm on my second set of twin iron keels....
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