I have given up on scraping the old antifouling and am having the hull sand blasted at great expense but a huge saving oif time, patience etc. when the cast iron is revealed what, and when, do I paint it with before antifouling?
As soon as the blaster has finished get at least one coat of paint on the keels to stop flash rusting(wipe it down with a thinners damp rag first)most blasters will do this for you if you give him the paint and a brush.I have used Blakes keel primer in the past with no problems
Epoxy mastic is very good , it's a two pack basically mixed 6 to 1 .I used it to paint over the welds on my tug and found it to be very good .The only concern is the temperature it needs to be 5 degrees or more to cure , mind you I used a heater to get it to touch dry .
You can get it in one litres quantities and they post it to you .
I had two litres and it cost about £46.00 .Postage wont be very much.
I got mine from PDS in Peterborough 08709090093.
The man who did mine used a clear epoxy primer within minutes of completion of blasting. I then overcoated with VC Tar after a week or so, which was to allow some of the internal porosity to dry. No action has been taken since, except to apply Copperbot. That was about 6 years ago and the VC Tar is rather brittle now but generally the keel is in pretty good condition.
20 years ago I ground off my iron keel a painted it with epoxy tar.When I sold the boat last year it was still good.I think the bitumen gave the epoxy a bit of elasticity.A minor problem in 1st rear was that the bitumen bled through, so white antifoul went pink.Original paint was International which I don't think is now a available but I guess VC Tar is similiar.
I had my cast iron keel sandblasted about 3 years ago, a coat of zinc prima was applied as soon at the sand blaster moved away as the iron changes from silver grey to brown in minutes; the prima used was the same as that used on steel piles on large jetties. We then filled any low areas with epoxy resin mixed with fillers and sanded it smooth. Then the topcoat was applied, it to was the same as that used on steel piles under jetties, I think it’s called Interzone. Tar Epoxy paint is no longer available here as they are carcinogenic. The Keel is still in mint condition, I’m advised the paint should last 10 tears or more.