Everything you wanted to know about Rusty Iron Keels but were afraid to ask...
First 235 Wing Keel: click for full 1200 pixel version
Ye olde First 235 wing keel before sandblasting and treatment. This is the typical pitting you see after salt water immersion for several years or more. The wings actually have a fiberglass/epoxy coating over the iron. This sample also had enough oysters on the wings to feed 12 people with or without visit to emergency room...

Below are the results of a bewildering search over the net and newsgroups for ideas on fixing the dreaded rusty iron keel, certainly the bane of existence Top 5 for the sailboat owner unlucky enough to inherit such a design. Of course, lead is not without its problems too but iron is surely a bit more difficult to maintain. What you save in initial ducats you will surely sweat away in hours toiling with solutions. And solutions seem to be a dime a dozen with different approaches depending.

What am I doing? I am going to go with the POR-15 approach (gray) after wire brushing and grinding the keel (My first option of sandblasting fell to complications in renting the gear). Various newsgroups online (Tanzer etc) have reported excellent results with virtually no rust return. See more POR-15 info via their FAQ. After this, I will be applying a full barrier coating, fairing, and bottom paint. I hope to add a page on this in place of below. Stay tuned.

For the fairing compound, I chose to use the oft acclaimed but expensive West Systems 105/206 Epoxy Resin/Hardener solution thickened with #407 Low Density Filler for the ease of sanding and excellent consistency (Filler chart). While West Systems is a more costly, it is certainly great to work with while being simply the strongest solution. See details below.

F235 Iron Keel Escapade: The Ordeal has begun....

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.

Stay tuned for more pics and report.

I have not yet taken pictures of the keel after the fairing with WEST SYSTEMS. But I can say this POR-15 is really good stuff. PICS COMING.

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Here are a few other articles and posts relating to the Iron Keel Dilemma. Soak it all in and decide what you think makes the most sense...

Preventative Maintenance and Repairs
From Practical Sailor.com .pdf file
by John Pazereskis

Remedies for Rusty Iron Keels

The best way to treat an iron keel that is rusting is to sandblast the entire surface and apply an epoxy based coating system. But that's not always feasible or desirable. Because of the mess involved, many boat yards do not allow sandblasting. Even when this is permissible, a complete recoating job also means a complete refairing job, and that in turn means lots of slow, dirty work if anything approaching a proper, smooth foil is to be achieved.

Because of the problems involved in completely refinishing an iron keel, patch painting of rusted spots is often the only practical way to go. Begin by cleaning the rusted spots as thoroughly as possible. Take your time here as this is the most important step. Chip off any scale with a cold chisel or welder's chipping hammer, then wire brush (use a drill-powered brush where possible) and sand with coarse paper until you're down to clean, bright iron. Use fine sandpaper (150 grit) to feather in surrounding, sound paint, and you're ready for your new coating. Get paint on the bare prepared iron as soon as possible. Iron will begin to oxidize almost immediately, and leaving it bare overnight will make much of your preparation go for naught. Unfortunately, the best possible anti-rust coatings (those with epoxy bases which are true vapor barriers) are not compatible with other paints. Epoxies just won't stick to other coatings; and, thus, because patch painting must lap over onto other paint, epoxies can't be used in this application.

My own experience backs up the recommendations of the paint manufacturers. The best coating to use in patch painting iron is zinc chromate paint. All the major manufacturers of marine coatings make a good zinc chromate. Take your choice and follow the directions. The most important rule to follow is three coats must be used. The object is to form as nearly an impenetrable barrier to water as possible, and three coats give a far better chance than one or two. Patch painting isn't the ultimate answer. Careful preparation and three coats of zinc chromate paint, however, make for an economical and effective solution.

To make sure your keel doesn't begin to corrode again, you must completely isolate the surface of the keel from the bottom paint with an epoxy barrier. This is a two-stage process. First the keel must be primed with a vinyl primer, such as Regatta Vinyltex 50/51 or Interlux Vinyl-Lux Primewash 353. The primed keel can then be overcoated with an epoxy mastic such as Regatta Epoxydur Mastic 3630-3631. Several coats of the epoxy mastic can be used. The thicker the
coating, the more effective the barrier. The epoxy mastic does not sand well, so special care must be taken before application to get a smooth keel surface. This same epoxy system can be used on iron keels that have been blasted or ground to bright metal, but is only effective on a completely clean surface free of any rust or scale. Surface preparation and the timing of application of the coats of vinylepoxy systems are critical, so the manufacturer's instructions must be followed to the letter. The only drawback to epoxy sealing of an external keel is that it no longer functions as a good ground plate for Loran and single sideband, or as access to ground in a lightning protection system. To compensate, you should install an external grounding plate.

Some newsgroup interchange on the subject below

Subject: Re: Fairing/painting cast iron keel
From: Tom Dacon (Tom@dacons.com)
Newsgroups: rec.boats.building

click for 1200 pixel viewThe technique I've used on two different iron-keeled boats, over a total of twenty-eight years of ownership, with excellent results is:

1. Sandblast the keel, going after all traces of rust, until the metal is what they call "white" (an uniform light gray).

2. Immediately afterwards (within minutes), paint it with Ospho (phosphoric acid), going around and around it until the Ospho stays shiny. Let this dry. Try not to let the Ospho-treated surface stand overnight in humid conditions - it's hygroscopic, and the next morning you'll find some rust spots down in the pits. If you do, wirebrush them and Ospho them again.

3. If there is pitting that you want to fill up, fill it with an epoxy-based filler. In southern California, we use something called Red Hand, which is a two-part filler that mixes up dark red. They named it Red Hand for a good reason

4. After the fairing compound has cured, fair it with a sander, body file, or whatever you need to use to get it smooth.

5. If the fairing process exposed some bare metal, as it almost certainly will, re-treat the exposed metal with Ospho.

6. Give the keel several full-strength coats of a barrier coat. This might be vinyl red lead, which is what I use, or some other barrier coat recommended by the paint manufacturers. If you use vinyl red lead, which comes in various colors, use two different colors for the coats, so that you can tell that you're getting full coverage.

7. Finish off with several coats of bottom paint.

This treatment has served me really well. When I sold the first of my iron-keeled boats, a couple of years after a treatment like this, the buyer was surprised to hear that the keel was iron - there wasn't a rust spot on it. On the boat I have now, there's usually a little bit of repair that needs to be done at each haulout, where the ballast keel joins the wooden keel timber. I just scrape it clean, wirebrush it, Ospho it, fill it with thickened West epoxy, and paint it.

Tom Dacon

More comments...

I have put two coats of epoxy paint over cast iron keel and it stopped rust completely. After that you can do something for a smooth finish but dont sand through the epoxy. by the way i have been told 6 coats of epoxy is necessary to stop osmosis but this experience tells me two is good enough

In any case, the iron keel should have a coat of paint before the anti-fouling is applied.Without a non-metallic paint as a barrier between the iron and anti-fouling paint, you have put 2 dissimilar metals together. Probably common knowledge, but bears repeating.

As the owner of a boat that has probably spent close to 30 years in salt water (with an iron keel) I would say don't worry if it has been maintained.

My Grampian 23 has a cast iron keel that was originally coated (epoxy or fibreglass?) but it now has several areas where the original coating has been damaged.

When I haul it out (every 2 years) I scrape off any loose paint, and rough up the good paint. Then I prime the iron casting followed by good bottom paint.

I am generally just seeing a bit of surface rust and even this has been reduced greatly now that I moved the zincs from their previous owner installed location on the fibreglass rudder (!!!) to a cleaned off area on the iron keel.

The boat is in the water about 103 weeks out of every 104 (2 years) due to our mild climate and this maintenance routine seems to keep corrosion in check.

Subject: Painting a Cast Iron Keel
From: Chris Webb (chris@2020engineering.com)

Can anyone give me some reccommendations about painting the cast iron keel on my 1967 Cal 20?

Last year I decided to do it right and grind it down to bare metal, osfo it, then do a coat of epoxy paint and then bottom paint.

Two weeks after she came out of the water in october it all peeled off to the osfo.

Frustrated in Bellingham, WA

Subject: Re: Painting a Cast Iron Keel
From: Capt. Neal® (Capt.Neal@Bigfoot.com)

I have a cast iron keel on my Coronado 27. Your mistake is using the Ospho.

This what your should do. Have the thing sandblasted to bare metal. Coat it with a layer of Zinc Chromate paint right away before any rust develops. Let the paint dry 24 hours. Get a couple gallons of the thick two-part epoxy--not the paint, the glue type epoxy. Mix it up in managable batches and trowel it on as smoothly as you can. Lay it on thickly. Try to make it as smooth as possible with minimal ridges. Let it dry 24 to 48 hours and get after it with a DA or rotary grinder with a light touch. Remove all the ridges and trowel marks and then put bottom paint directly on the roughened surface.

Nothing should fall off after this application.

Respectfully, Capt. Neal

For what it's worth, here are my suggestions. First, you can get rid of rust, but you can't stop it (from coming back, that is). You can only slow it down from coming back soon. So, here goes: go down to bare substrate, use a chemical conversion mixture of phosphoric acid or auto paint supply stores do have a rust conversion product that is quite effective. There are various companies that make this type of product, you should have no trouble finding one or the other. Take you time with this step, get rid of all the rust or you will waste your time and money. Next, and on the same day prime with a 2-part epoxy primer. (reason: clean bare metal begins to oxidize immediately) Over this you can apply a primer-surfacer which has filling ability because it's thicker, this will give you some "meat" to rough sand without breaking through to the bare metal again. Next, you can apply your fairing compound. (incidentally, both fairing compound and bondo are porous, it's just that fairing compound is stronger and flexible for boat bottoms.) Because of this porocity you must then (after fairing to shape) apply several coats of epoxy primer again. Now you are ready for your antifoulant paint. International makes a variety of bottom coats to suit your needs and budget. US Paint makes an antifoulant paint but its expensive. Whatever, your choice. The key is take your time with the preparation, and you will have a job that lasts (not forever, but long enough). Of course, every time you haul out check the bottom carefully. Have fun!




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