Saving £100s with DIY -- TREATING THE KEEL (PART 1)

Saving £100s with DIY -- TREATING THE KEEL (PART 1)

More rust than expected. Copyright (c)
Froo Gal 2015. All Rights Reserved.

You may have noticed from earlier pictures of FROO GAL's keel that it was rusting a little. So, when we lifted the boat for 10 days to get the seacock replaced (by a professional), we decided to repair the few patches of antifoul on the keel. What could go wrong?

Well, the lift out went fine. Then it rained like cats and dogs on the day that two of the FROO GAL crew had taken off work -- that's  Britain in July for you.

We were up at 0700 the following morning; had a snack for breakfast and were working on the boat by 0730. On inspection, the small patches of rust weren't: most of the keel was suffering from corrosion or the early signs of it. The pitting seemed to be starting under the antifoul and had spread over most of the surface with 50% density over one side of the cast iron keel and perhaps 20% of the other side.

We don't know how why it is so bad, as the keel was professionally shot-blasted

Red Oxide Primer. Copyright (c)
Froo Gal 2015. All Rights Reserved.

back to bare metal and covered with an epoxy primer prior to the antifoul application, not two years ago. Was it galvanic corrosion, poor surface preparation or just one of those things? Perhaps we will never know. The yard had cryptically said that the antifoul might not adhere very well to the keel.

So what should we have done? We only had enough antifoul (which was special mail order and not available from local suppliers) for perhaps half of the area. And slapping it on top of the damaged area was not going to be a fruitful repair.

Two Part Epoxy Primer. Copyright (c)
Froo Gal 2015. All Rights Reserved.

We had nice days spare with the boat out of the water, but with three or four needed to allow the antifoul to cure and full time jobs we were rapidly running out of time. A week of careful planning for the original scenario was rapidly replaced by ad hoc improvisation bordering on panic.

We had already decided to add an anode to the keel. We had planned this in advance and had brought an electric drill, special drill bits and die set. We had not bought the anode, but it would be easily sourced in from one of the local chandlers. So we decided to drill and tap an M6 threaded hole. The drill worked well, considering the hardness of the cast iron. The good quality die cut the thread easily... until one of the crew got a little too enthusiastic with the last turn, hit the bottom of the hole and snapped it off flush with the surface of the keel.

Fortunately, after having bought a cheap carbon steel tap and die set to replace

316 Stainless Bar in Tapped Hole.
Copyright (c) Froo Gal 2015.
All Rights Reserved.

it (a complete waste of money is all likelihood), we found that the anode best suited for the application needed an M10 threaded hole. This aforementioned crew member cut without drama. We bought some A4 (316) stainless steel threaded bar, nuts and washes. Having cut the bar to length this job was finished, save the attachment of the anode, which would follow after the surface treatment of the keel. The broken tap would be left in place -- a fantastic new corrosion site!

We used the wire brush on a drill to remove the loose rust. Decreased the surface with white spirit and covered the whole keel with Red Oxide Hammerite primer, with a brush to get the primer into all the holes. (This primer layer may prove to be a mistake). We let this cure/dry for three hours.

Covered Pitting. Copyright (c)
Froo Gal 2015. All Rights Reserved

After some GOOGLE research, we then applied two coats of two-part epoxy primer. The instructions on the tin seemed to suggest that this would be compatible over the Hammerite primer, which we had lightly sanded to provide a key. After the first coat, we had to let it cure for three hours (which turned into over four as it was still tacky after three). We then read the manufacturers free painting and treatment guide. This suggested that over-painting a one part primer with a two part primer is not compatible. But the guide does not say why or the effect of getting it wrong. Various yacht forums' threads say the rust treatment adds no additional value to epoxy priming. So it seems likely that the Red Oxide Hammerite will prove to be a mistake, as it may well cause the epoxy layers to lift and peel prematurely -- only time will tell.

Still doing it ourselves saved hundreds of pounds (sterling) of boatyard labour costs and we know exactly the condition of thew boat and preparation of the surface coating. And we now know how to do a good job when we inevitably have to do it again (perhaps next year).


We'll order more antifoul system and apply it later in the week... and pray for dry weather (it is raining again today).