Keel priming

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Paddydog`1

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My iron keel needs taking down to the bare metal because rust is sprouting all over through the previous epoxy. Several layers of antifoul also need removing. Given that I dont want to do it myself with a grinder etc, what is the best method to use?. And also what is the best primer or treatment prior to antifouling?
 
To do a proper job you HAVE to get it grit blasted back to bare metal. paint needs to go on right away and ideally you need it to be warm with low humidity as well!

As for paint a couple of coats of zinc rich epoxy followed by 2 to 6 coats of high build epoxy then AF of your choice.

Follow the manufacturers instructions CAREFULLY and FAITHFULLY about recoat times.

I used to have a steel boat and this worked for me.
 
My little motorsailer has a steel rudder. I ground it back to bright metal and painted it with a couple of coats of Primocon before antifouling. Rust was coming through before it was even launched! Whereas grit blasting and epoxy on the keel of my Sadler lasts for years underwater.
 
One thing I've noticed is that my keel shows rust spots after a few days on the hard that weren't there imediately after hauling out.I believe cast iron rusts more readily in contact with air than it does underwater.
 
I find a hard steel wire brush in an decent quality angle grinder the next best thing to blasting. Wear a recent respirator.

I favour non zinc based primers such as epoxy tar or chlorinated rubber. There's no substitute for thickness so put plenty of layers on.
 
>I believe cast iron rusts more readily in contact with air than it does underwater.

Rust needs both air and water. Sea water contains air, as in your wake bubbles. Air also usually contains moisture.
 
I had several boats with iron keels and never had to resort to grit blasting, we used a wire brush followed by at least four and usually five or six coats of Primocon over the residual rust and it seemed to protect for at least five years. Primocon used to have a lot of bitumen in it which leached through and discoloured white antifouling but otherwise it was an effective product.
 
I've mentioned this before.

We gave a boat to the ITV Telethon, and it was a prize won by guessing the weight of the keel. I spoke to the National Physics Laboratory.

They would weigh it (to the nearest Gram) on condition that it was still at at least 50C from casting.

Puzzled, I asked why. Because it absorbs at least 1% of its' mass of Water as it cools. Army collected it fresh from the mould, wrapped it and delivered it from Cornwall to Teddington.

So. Your keel has water in it. Surface coatings will have a hard time. Which is why some builders encapsulate them in GRP at the outset. Great until you run it aground in anything but mud.

My Cowes week in '86 was ruined by bouncing an X-Yacht 402 on Bramble Bank. Thereafter we were rubbish upwind. On lift-out we saw why. You would struggle to find a better lift dumping, drag creating keel mod.
 
>So. Your keel has water in it.

I find it difficult to believe that cooling iron aborbs water. There is no mention of it on the National Physics Laboratory's site although you quote them. Properly applied zinc rich epoxy paint followed by ordinary epoxy fixes rusty keels after blasting, so the surface coatings don't seem to have a hard time.
 
This is a question that has come up many times on the forum. The best solution is thought to be blast clean to SA2.5 immediately followed by zinc rich primer followed by decent hi-build primer and topcoat. Most people however do not grasp the nettle (including me) and use a wire brush on angle grinder or similar followed by Fertan or Kurust (same stuff, different name) followed by Primocon, topcoat and anti fouling. We accept that the process will have to be repeated after a few years.
 
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