Rusty keel?

[mikefleetwood]

Musketeer has been lifted out for the Winter. The lift-out included pressure wash/scrape all the weed growth off below the waterline. I've noticed a couple of rusty patches appearing, through the old paint.

What is the best way to treat these before antifouling?

Many thanks.

 

[Concerto]

Grind the affected areas. Treat with a rust converter like Fertan. Then coat the treated areas with at least 6 coats of Primocon. Then antifoul.

All cast iron keels are porous and can rust. The above treatment has worked for me, but every time Concerto comes out of the water there is always somewhere to treat. This has been reducing over time, but will never go away completely.

 

[mikefleetwood]

Thanks for that.
The existing antifoul is Hempel Cruising, so I probably ought to use Hempel primer - do you think that would work just as well as the suggested International product?

 

[Dellquay13]

Thanks for that.
The existing antifoul is Hempel Cruising, so I probably ought to use Hempel primer - do you think that would work just as well as the suggested International product?

I use the hempel underwater primer (with the aluminium flakes) on my iron keels. I brush any fresh rust clean, quickly get 3 coats onto these patches, one final coat all over the keels then get the hempel tiger xtra on. 3 coats of tiger lasts two years afloat for me

 

[MikeCC]

Depends how much work you want to do. I stripped my keel completely as there were so many rusty areas.

I used a couple of coats of an industrial metal epoxy primer followed by filling and fairing. Then 2 coats of Hempel Light Primer (2 pack epoxy), followed by vinyl primer then antifoul. After 4 years, only one spot has come back.

As long as you get the first primer coat on to clean metal, don't bother with a rust eater type product. Give it a final sand and wipe over with thinners right before painting.

 

[Concerto]

Thanks for that.
The existing antifoul is Hempel Cruising, so I probably ought to use Hempel primer - do you think that would work just as well as the suggested International product?

No problem in changing different antifouling suppliers.

 

[PabloPicasso]

I wouldn't use a grinder. Too aggressuve unless it really is very bad.

I've had some succcess:
# wet sand back the worst of it by hand
# you could use a rust converter like Ferton but not essential
# several coats of red or grey oxide paint
# anti foul as usual

As said, cast is pourous so likely to reoccur. No big deal. Just repeat next time you're lifted out.

There are a lot of old boats from the 1970s & 1980s ++ with cast keel rust issues ongoing to no great ill affect.