Thursday, April 23, 2009

How to refinish an iron keel

Update: Canadian Tire has started selling both the POR 15 Metal Prep solution and  POR 15 paint.

Today at the Chandlery I found out a little secret... the shops that sell Interlux epoxy and paint products don't recommend using POR-15 because they don't carry it, and they make money by promoting the Interlux primers instead. Unfortunately Interlux doesn't manufacture a product like POR-15, so if you take the advice of the Interlux dealer you might be dealing with rust every couple of years on an iron keel. Interlux makes great products and I recommend them below, but for an iron keel you should start with POR-15 first, and then move on to the Interlux.

I refinished my keel in last spring and it's still clean as a whistle with just a smidgin of oxidation around the hull keel joint, which I didn't have time to finish properly. I'm really happy with the results so far and will probably carry on and deal with the hull keel joint this month or wait till next year.

(Update: as of spring 2014 the keel is still in great shape, and the hull-keel joint looks good, too. That's seven years and counting. Only the very bottom of the keel, which I couldn't reach, has some rust-scale on it. A project I hope to tackle in stages by raising the adjustable cradle pads and putting some 2x4's under the keel when I haul the boat out in late fall.)

This is a pretty big job, but it's doable. As a one-man job it took me about two weeks of steady work on evenings and weekends, without having much prior experience. Given the motivation, perserverence and elbow grease, it can be done by an amateur. There's always the alternative of hiring a pro to drop the keel, sandblast it, and professionally refinish it, and if you have a grand or so to spare, you might consider it. If that's not an option and you can get an extra set of hands to help, I wouldn't hesitate to tackle it. Here's what I recommend:

1. Get the old paint and rust off.

Use a grinder for this. Scrapers don't work, drills don't work. Grinders work good. I used a very aggressive sanding disk (designed for metal) with a backing plate, and also the meanest looking wire brush attachment I could find in Canadian Tire. My first attempt was using scrapers and they did almost nothing but remove some surface rust. The sanding disks worked well but I went through a half dozen or so rather quickly. The wire brush was pretty good as well, and by alternative between sanding disks and the wire brush, the keel cleaned right up.

It's very important to wear proper protection for this step including a respirator and protective glasses. The dust from sanding and grinding the bottom of a boat is toxic, nasty stuff and you do not want to breathe it in or get it in your eyes.

It's not essential to get down to bright metal. You're not setting your table with it. The bits of original primer that stick on the keel won't hurt. With a grinder you'll quickly discover all the rust pockets and make short work of them.

Some owners with heavy rust scale have reported that an air hammer works best. It depends how bad your keel has deteriorated but if you the rust is coming off in heavy flakes, renting an air hammer might be your best option.

2. Metal-Ready

Also known as POR 15 Metal Prep, you can get this at Canadian Tire now. This is a recommended prep before POR-15. It contains phosphoric acid. You can get other brands but this is the one I got from the truck shop that sold POR-15. Spray it on, and any remaining rust or oxidation that has happened since your last grinding session will magically convert into a zinc phosphate. You're supposed to wash this off with water. I was very reluctant to wipe my bare metal keel down with river water, but I did, and it was fine. Metal-Ready is a water based solution itself. It didn't start to rust like I feared, but instead rinsed most of the residue away and left a good surface for painting. This stuff works amazingly well to obliterate rust, and the zinc phosphate film left behind is apparently a good prep for POR-15 to bond with and helps prevent future corrosion.

3. POR-15

You can now get POR-15 at Canadian Tire. POR-15 is hands down the single best rust-preventative coating on the market today. It forms a chemical bond that converts rust into a rock hard compound and locks out corrosion. Unlike other coatings it actually cures and becomes harder in the presence of moister, so it's ideal for underwater applications like keels. I did three coats with about 8 hours between coats. It dries ultra-hard so you need to put the next coat on while the previous is still a bit soft.

4. Interprotect 2000

This is the famous epoxy bottom coat. I did not put this over the fiberglass hull because my boat shows no signs of osmosis. On the recommendation of a local yacht repairman, I did five coats over the keel, very lightly sanding the POR-15 first with a fine grit to provide a bit of tooth. I had no problem painting Interprotect 2000 over the POR-15.

5. Fairing compound.

This is getting to the last stage. Fair the keel with a fairing compound and sand the compound smooth once dried. Be very careful when sanding not to sand away your bottom coats. I applied fairing compound only to a few spots that had obvious pitting, and then gently hand-sanded those spots smooth afterwards, being careful to stay away from the epoxy bottom coat. The fairing compound was blue and the interprotect was gray so it was easy to tell the difference. How much time you spend on this depends on whether you want a racing bottom or just a respectable cruising keel. Mine falls in the "respectable" category but I'm likely to do some more fairing work with time and conditions permit. Because time was running low, I faired up the hull keel joint without caulking. I recommend treating the hull keel joint differently however. I'm planning to dremel out the keel joint and caulk it. Filling it with fairing compound was a timesaving measure to be ready in time for last year's launch.

6. Hull Keel Joint

Update: I have written about fixing the hull-keel joint here:

The basic process is to clean out the joint with a Dremel tool, dab some Metal-Ready onto the exposed keel edge, paint with POR-15 using a small brush, over-coat with Interprotect 2000, fill in the gap with Sikaflex 291 caulking, and then paint over the whole mess with VC-17 antifouling.

7. Top Coat

On top of the fairing and caulking of the keel joint, put a top coat of Interprotect 2000. It mainly covers up the fairing compound and gives you a consistent colour and base for the anti-fouling layer. Functionally it doesn't add much.

8. Anti-fouling

Everybody uses VC-17 around here. If you sand the old antifouling off your hull, use a really good air mask with dual filters and snug fitting seal around your nose and mouth. You do NOT want to breath this stuff in, it is highly toxic. Also wear safety goggles whenever you're working under the boat. Any drops or tiny spatters of paint, flakes of rust, or other nasties that land in your eye can cause serious damage. The VC-17 goes on watery-thin and dries fast. You have to work quick with this stuff. Tape the waterline and give everything below it a thin coat of VC-17. It's as shiny and bright as a new penny, and looks beautiful.

9. Launch

Watch all your hard work disappear under the water! Pray that it holds out for the season (and hopefully for another ten years). Iron keels add a unique dynamic to boat ownership and will always keep you wondering in the back of your mind how that big hunk of iron is holding up. Sure those keels all could have been made of lead with no fear of corrosion, but what fun would that be?!


Anonymous said...

Very helpful-thanks. Just starting the process in Gloucester, MA on a Pearson 26

Anonymous said...

Starting a similar process with a Westerly 25 bilge keel in Orange, CT. Fun, fun... I will say that an air hammer makes short(er) work for removing scale and rust.

Unknown said...

Thanks for all your tips - I did my 1970 Grampian 26 this spring and I think it turned out well (We'll see once I haul it this fall!)

Darren said...

Great, glad it was helpful. As of 2017 still no rust on my keel except the very bottom where I couldn't reach. One day I will get to that.

Jeremy said...

Hello Darren
This post is upmost informative and useful.
I'm in the process of selecting a repair solution for my Tanzer 26 keel. I was looking for the best product combination for a long time rust protection.
If you still don't have rust since 2009 it's good news. Unless you have rust under the fairing. My keel was repair by a previous owner and the rust was growing under the fairing. Thank a lot, Maxime from Montreal

Darren said...

Hey Jeremy, glad it was helpful. I had more time back then to work on my boat, but thankfully after 10 years it is still holding up well. A lot of Tanzers have to deal with rusty keels, that's just the result of Tanzer using cast iron. It was not a great choice of material, but Tanzer's are very well built and have held up amazingly well for 40 years! A lot of owners used to apply VC-Tar and then VC-17 on these keels. That was the standard approach, and from what I've heard, Tanzer owners had to deal with rust every few years. It's not surprising or unusual that rust would grow under the fairing compound. I don't think it really affects performance either, unless you are in the top 1% of racing sailboats with a glass-smooth bottom. Anyway I would just get in there with a grinder and knock most of the rust off (some people with severe rust recommend a power-hammer to knock it off in large chunks). But once you get most of the crud off, that Metal-Ready + POR-15 treatment should keep you good for a while. Plus it's fun to work on boats!! :-)

Hildingur Mahanti said...

Hey, I am going to be doing this POR-15 + Interlux 2000 treatment over the next month, the only thing that is not clear to me is, which is the faring compound you used over Interlux 2000?

Darren said...

You probably want to go with the Interlux Watertite Epoxy Filler. Whatever I used was blue, and from Interlux, but that’s all I remember.

boubougazelle said...

Thank you very much for this article. I did the exact same procedure. I had one problem though... and it showed after my sanding of the fairing coumpound. At step 1, you should add a step: "carfully sand your keel with 80 grit sandpaper using an orbital sander or the same sander that you will use for your fairing later on." After doing all of the work up to the fairing coumpound, I sanded it but doing so, did also sand little peaks on the keep, bringing down everything almost up to the metal. At least to the POR-15. So I had to go back and touch-up againd a 4 coats of interprotect on those spots. Making the process very, very time consuming. Adding a little sanding stage earlier would have added 30 min of sanding instead of 2 days of interprotect ! :)

Darren said...

Thanks for reading and congrats on the "new" keel. I added a sentence or two to the fairing step. In my case, and what I recommend, is to fair up only the spots that are obviously pitted and very gently hand-sand just the fairing compound smooth in those spots afterwards, being careful to stay off the interprotect bottom coats. The grinding and sanding I did in Step 1 left a very smooth keel surface in my case, so there were no bumps or ridges to worry about. When fairing, some people prefer to cover the entire keel with fairing compound and then sand the entire surface flat. This can produce an extremely smooth keel surface but is only well suited to non-ferrous keels such as lead antimony or fibreglass-encased keels, imho, or you run the risk of sanding through to the iron. I imagine the extra work you ended up doing will pay off with an exceptionally streamlined keel though.

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