Primer for cast iron keel

[Sea Change]

Receiving conflicting advice on this.
I've got a cast iron keel which has previously shed its coatings. Going to try taking it back to bright metal and priming.
I don't know if I can get it blasted but I'll look in to that as it's seemingly much better.
Some suggest using standard epoxy straight on to the bare metal, which is tempting because there's never any harm in having epoxy in stock.
Someone else has suggested products called Ameron or Corotech which are more specialised epoxy primers.
And then there's stuff like the Epiphanes primer which has zinc in it, which sounds good.

Any thoughts? Boat is a 70s Moody if that makes any difference!

 

[chris-s]

For sure there are loads of options out there. What I used on the bilge keels of our previous boat, after knocking it back with a Tercoo (?) and treating with phosphoric acid for any remaining rust was Jotun Penguard Express ZP. Walking past the boat in the yard several years later it shows no sign of rust on the keels except where it’s been dragged along the bottom edge.
I would use it again without hesitation.

Chris

 

[PeterWright]

Hi Sea Change

You're right that grit blasting is the answer for getting rid of the rust, rather than burring over the pores and trapping the rust in them, which is the consequence of wire brushing. Best to grit blast, then pressure wash with fresh water to get the worst of the salt out of the pores then a light blast over to clean off the gingering from the wash. Try to get the first coat of epoxy primer on the same day as the blast / wash / blast and make sure you capture all the waste for safe disposal.

You should use an epoxy primer which is moisture and rust tolerant. I don't know Ameron, Corotech is moisture tolerant, but not particularly formulated for the marine environment whereas Corrocoat is produced for just that use, as is 3M Scotchkote GP120 (I think that's the latest version, they keep developing it and changing the name).

Marine | Corrocoat https://www.promain.co.uk/specsheets/EpoxyPrimerGP120_Promain.pdf

We used an earlier version of the Scotchkote (152LV) on our Moody 425 13 years ago, wanting to put Coppercoat on top of it, and it's all still fairing well, except that I ground most of the paint off the bottom couple of inches by cutting a groove in the bottom of a Dutch canal a few years back. Oh, and the Coppercoat is not so effective any more, but they only claim 10 years. We actually had the keel and the hull below the waterline blasted, then painted the whole lot with 3 coats of the primer before Coppercoating. If you plan to blast the grp, make sure you use a blasting contractor with experience of blasting grp - our guy left a nicely matted surface , but took very little gel coat.

Peter.

 

[ashtead]

I’m sure Tranona might have thoughts but a simple solution is to use Fertan and then your antifoul primer and then antifoul
It might be out of budget but would Coppercoat be a solution ? On an old Moody I wouldn’t be that worried to be honest -just accept each year you have to sand back and re fertan

 

[Tranona]

Not had much success with Fertan. As already suggested there is a fundamental difference between grinding or wire brushing and blasting as preparation. The former does not provide a good enough base to take epoxy and a good primer such as Primocon or Jotun Vyniguard is as good as any.

The keel of my Bavaria was ground to remove the factory coating then epoxy and Coppercoat but starting to breakdown after 3 years so I had it blasted as in post#3 and 6 coats of Hempel Hempadur before Coppercoat. Not sure how well it stood up as sold the boat 2 years later. Seem to have had better luck with my GH as although the ballast is encapsulated the bilge plates are steel and I had those blasted and epoxy coated. Expensive - around £800 but after 15 months in the water no sign of any deterioration.

The castings on early boats like yours were very poor with lots of impurities and imperfections so very difficult to get a good clean surface, and while blasting is obviously better prep it is expensive and not foolproof, So if I had a keel like that I would be tempted to stick with the basic primer and accept regular patching.

 

[ashtead]

I1 think that means you just have to live with it and treat as best you can each year. Do ask on mpoody owners website to seek other views

 

[Sea Change]

Thanks all
I'm maybe asking a bit much but I should mention that I don't really follow the standard 'haul out every year' pattern of ownership. We're full time liveaboards and this will be our first haul out in over four years (barring a brief emergency haul out where we didn't have time to do much work).
So I'm looking to get the keel in to a state where I can scrub off fouling in the water. Patching recurring rust isn't really a good option.

The boat is already coppercoated and I'm planning to replace this with more of the same. But when the previous owner had the CC applied, it didn't adhere well to the keel and he eventually started using conventional AF there. I'm tempted to give CC another chance there. Whatever I put on the keel has to be properly scrubbable and I'm not sure if any conventional AF truly is.

 

[ridgy]

I used two coats of Fertan on mine last winter followed by primer and antifoul and its still looking good this winter. Gives me confidence that I could slap another coat of antifoul on this winter and it may keep going.

 

[vyv_cox]

My keel has been grit blasted twice. Within half an hour it was coated with standard West epoxy. The first time was winter in Wales, so a bit on the damp side. That lasted about 13 years. The second time was in Greece, now about 15 years ago and still not too bad. Occasional touch-up required but not enough for a total replacement.

 

[Tranona]

Thanks all
I'm maybe asking a bit much but I should mention that I don't really follow the standard 'haul out every year' pattern of ownership. We're full time liveaboards and this will be our first haul out in over four years (barring a brief emergency haul out where we didn't have time to do much work).
So I'm looking to get the keel in to a state where I can scrub off fouling in the water. Patching recurring rust isn't really a good option.

The boat is already coppercoated and I'm planning to replace this with more of the same. But when the previous owner had the CC applied, it didn't adhere well to the keel and he eventually started using conventional AF there. I'm tempted to give CC another chance there. Whatever I put on the keel has to be properly scrubbable and I'm not sure if any conventional AF truly is.

Then worth giving it a go if you can find somebody who will do a good job on blasting. You are better placed than most to do Coppercoat because of the temperature issues, but will maybe have to watch humidity. I did mine in the summer of 2020 in the break between lockdowns with over 2 weeks of warm high pressure weather.

 

[KREW2]

Wire brush, fertan three coats primacon and antifoul. Following years wire brush the rust patches, apply fertan, patch prime, full coat of primacon to stabilize the old antifouling and antifoul. Did this every year, after two years had minimal rust coming through.

 

[Daydream believer]

Thanks all
I'm maybe asking a bit much but I should mention that I don't really follow the standard 'haul out every year' pattern of ownership. We're full time liveaboards and this will be our first haul out in over four years (barring a brief emergency haul out where we didn't have time to do much work).
So I'm looking to get the keel in to a state where I can scrub off fouling in the water. Patching recurring rust isn't really a good option.

The boat is already coppercoated and I'm planning to replace this with more of the same. But when the previous owner had the CC applied, it didn't adhere well to the keel and he eventually started using conventional AF there. I'm tempted to give CC another chance there. Whatever I put on the keel has to be properly scrubbable and I'm not sure if any conventional AF truly is.

I have given my keel 4 lots of coppercoat & never had much luck. In the end I just ground out the rust spots ,primed with one of international's metal primers & applied shogun 33. That actually worked very well. Not only did the shogun do significantly better than the copper coat on the rest of the hull but it held back the rust. I took the time to get a more even surface instead of the areas that were dipped where the layers of coppercoat had been removed for priming. So the next year I just abraded it & applied more shogun.

I looked at the keel just before Xmas & was surprised to see that there was only a couple of rust spots where originally there were loads.
A friend of mine, with a similar boat, that had copper coat applied professionally, from new, has done the same & reports a similar result.

 

[Sea Change]

Wire brush, fertan three coats primacon and antifoul. Following years wire brush the rust patches, apply fertan, patch prime, full coat of primacon to stabilize the old antifouling and antifoul. Did this every year, after two years had minimal rust coming through.

Problem is, I want to avoid lifting out every year.

 

[rogerthebodger]

Problem is, I want to avoid lifting out every year.

My steel boat was grit blasted and painted with epoxy tar over 15 years ago and launched 2009 and has no noticeable rust on the hull except where the hull paint was damaged when the marina break up some years age.

Wash with Hydrochloric and phosphoric acid the repaint with epoxy tad fixed the problem

 

[chrisD]

does keel rust really matter? Can it make significant damage to its weight?

 

[KREW2]

Problem is, I want to avoid lifting out every year.

There you are, problem solved. What the eye doesn't see the heart wont fret over.

 

[Sea Change]

There you are, problem solved. What the eye doesn't see the heart wont fret over.

I do see it, and there some funny stuff that likes growing on the rusty patches. Not pleasant to scrub it off.

 

[dgadee]

I slapped on a couple of coats of "red lead" after Fertan several years ago and it just needs re-doing again. I was surprised that it lasted so long - especially since it wasn't always lifted over the winter. I was going to coppercoat after blasting but have changed my mind and will just keep things low tech. Weather in UK is always damp so I think the cast iron will always be a problem - especially since it is such poor quality.

 

[robertager1962]

My steel boat was grit blasted and painted with epoxy tar over 15 years ago and launched 2009 and has no noticeable rust on the hull except where the hull paint was damaged when the marina break up some years age.

Wash with Hydrochloric and phosphoric acid the repaint with epoxy tad fixed the problem

I'll second this. I had major problems with my father's boat's cast iron keels but ground back to bare metal and them four coats of VC Tar 2, that was 20 years ago. Since then I have used this regime on my Centaur and now my Southerly 105 and use this as my go to method. One coat of Coppercoat epoxy with no Copper added as a primer over the VC Tar and then Coppercoat (or antifouling straight over the top.

 

[Sea Change]

Update: the yard don't offer blasting. So grinding it is.
This is making me wonder if I should reconsider my approach. I should maybe see how the keel looks after we lift out. Still not sure whether to try coppercoat or a different AF. The good quality scrubbable AF isn't actually any cheaper than coppercoat.