Primering iron keel

[guykane]

Hi, I had my 2 ton iron keel primored and painted 4 months ago, and there are already dozens of bubbles , 1 to 2 centimetre in diametre appearing all over the keel. I guess I’m seeing rust blots and I suppose there was a problem in preparation. The keel was sanded down to the metal, then primered with something called Interseal, then painted with Carboline antifouling.
Any suggestions for the next time I do the job?
Thanks!!
Guy

[a64pilot]

I’ll post largely to bring it back up for these that have painted iron keels before, I have not.
My assumption is that you either sand blast to white metal and then pretty much immediately prime and paint, or let a film of rust form and use a rust converter that chemically converts iron oxide to I believe iron phosphate, that really does seem to prevent rust.

It seems that once rust begins, even just a tiny bit and you prime and paint over it, that it will continue to rust under the paint.

Like I said though primarily I’m responding to get the ball rolling.

[guykane]

Hi A65 pilot,
Yes, it was sanded to white metal and painted within 24h. I think the contracter that did the job didn’t use a rust converter before the primer, and that’s the problem. What does everyone think about Owatrol or Primocon as a rust converter?

[billknny]

Originally Posted by guykane

Hi A65 pilot,
Yes, it was sanded to white metal and painted within 24h. I think the contracter that did the job didn’t use a rust converter before the primer, and that’s the problem. What does everyone think about Owatrol or Primocon as a rust converter?

If done correctly a "rust convertor" is not needed, wanted, or desired. And 24 hours for a cast iron keel is TOO LONG between blasting and first paint coat, especially if it is humid. Doubly so if the keel is cooler than the surrounding air and water condenses on it.

There are LOTS and LOTS of ways to do this wrong. Even wiping the blasted metal with rags is a no-no. You have to use a good paint system designed for cast iron (not steel!) and follow directions exactly and literally. If the paint system you are using recommends using a "rust convertor" then use it. Otherwise, DO NOT!

Primeocon is a primer paint, and a good one. It is not a rust convertor. If there is ANY rust when the first coat of paint is applied it will fail. "Converted" or not.