Cast iron keel prep

[vyv_cox]

I came to the conclusion years ago that the only way to keep the keel rust free is to grit blast to Swedish standard 2.5, epoxy prime, top coat and store under cover from then on.
Realistically, blast clean, epoxy prime immediately, apply top coat and anti foul. Carry out spot treatment in subsequent years including blast treatment. Basically the same system as used on oil rigs.

Your last sentence is true but the scale required is mind boggling. I used to have the painting specification for Shell production platforms. From memory, it called for two primer coats, six mid coats and something like the same number of top coats. All in epoxy. Probably the same as is now on the Forth bridge.

 

[ghostlymoron]

Your last sentence is true but the scale required is mind boggling. I used to have the painting specification for Shell production platforms. From memory, it called for two primer coats, six mid coats and something like the same number of top coats. All in epoxy. Probably the same as is now on the Forth bridge.

I was trying to illustrate the futility of it.

 

[Kelpie]

Need to order up the paint. Having searched old forum threads I'm none the wiser about the best choice of primer to go on the bare metal.
Primocon? The obvious answer.
Chlorinated rubber? Sounds like it might be a better bet. And it's actually cheaper, although I presume it won't go as far.

 

[Kelpie]

This is the stuff that's caught my eye:
PLASMOTEC One-Component Underwater Primer buy now | SVB

 

[MikeCC]

I used an industrial zinc-rich epoxy primer straight on to bare metal. Two (three?) coats, filling/fairing, two more of epoxy antifoul primer, then antifoul. Couple of spots after first year but they were flaws in the casting. Waiting to see how it looks in October.

 

[dankilb]

Jotun Vinyguard? (If available)

As an equivalent to Primocon, it has been ‘tried and tested’ on here.

5L is a bit much for some, but it’s useful for a host of jobs (and cheaper than 2.5L of the above!)

 

[dankilb]

I used an industrial zinc-rich epoxy primer straight on to bare metal. Two (three?) coats, filling/fairing, two more of epoxy antifoul primer, then antifoul. Couple of spots after first year but they were flaws in the casting. Waiting to see how it looks in October.

BTW… this ^^^ is pretty much the method we actually used! (After professional blasting)

I’m not 100% on the efficacy of the grind-vinyl primer-AF method myself. But I accept it offers far less investment of time, money, effort etc. (for an underwater lump of pig iron!).

(and p.s. - we can live with a couple of spots if it otherwise ‘works’ - but yet to re-launch!)

 

[Pavalijo]

When researching this some time ago I came to the conclusion (after reading many different advisory articles/posts) that with a cast iron keel the way to go was to sandblast and then use a needle gun to remove deeper rust, and then apply whatever protective coatings on top as quickly as possible. The research suggested that blasting alone was not sufficient.
I have continued to just wire brush (on a drill) plus Fertan plus as many coats of Primocon as time allows and each year it gets just a little worse.
Some day soon I may just get time to do a more thorough job, but my 3.5 tonne keel probably still weighs 3.4999 tons at 24 years old!!

 

[ghostlymoron]

Yes, agree that the problem is purely cosmetic. The keel is not going to disappear or significantly reduce in weight any time soon.

 

[DeepKeel]

Yes, agree that the problem is purely cosmetic. The keel is not going to disappear or significantly reduce in weight any time soon.

I thought that a large part of this debate is about providing something for the anti-foul to stick to, otherwise you will end-up with a forest down there that will cause real drag.

 

[PabloPicasso]

Great, I'll spot rust treat, prime, and AF before lift in.

I can't see that blasting, epoxying is worthwhile.

 

[MikeCC]

Should add that preparation was combination of Tercoo Blaster on a drill then polycarbide and flap disks on grinder. Tercoo was more economic than ripping through loads of polycarbide disks.

 

[Spirit (of Glenans)]

This is the stuff that's caught my eye:
PLASMOTEC One-Component Underwater Primer buy now | SVB

That's ruinously expensive, I'll just replace the tin of Vinygard that has lasted me ten years.

 

[Kelpie]

That's ruinously expensive, I'll just replace the tin of Vinygard that has lasted me ten years.

I need about three brushfulls...

 

[Tranona]

750ml tin of Primocon will do the job - expensive but like Blakes seacock grease a lifetime's supply (for patching the keel, not greasing the seacocks!)

 

[jwfrary]

Yes! In theory (i.e. TDSs!) a tie coat of underwater primer is recommended between epoxy and AF.

I say ‘in theory’ because I personally couldn’t say why! Sure someone will know…

Hempel light primer which is similar to hempadure two pack paint of very similar make up, indicates that the underwater primer should be applied when the light primer is still tacky followed by anti foul in the normal way.