Keel rust treatment, then antifoul.

[Jaguar 25]

What is the best method for treating surface rust on keels prior to antifouling.

Advice on a good antifoul for a drying mooring in Langstone harbour would also be appreciated.

 

[KellysEye]

The only way to stop rust coming back is grind the rust back to bare metal and use two coats of zinc rich epoxy, ensure humidity is low otherwise you risk flash rusting. Rust converters don't work I tried them on our steel boat and the rust always comes back.

 

[MoodySabre]

I just zap the rust spots with a flap wheel on my angle grinder, immediate rust converter and then underwater primer and AF. Each year a few spots come back but on 10 minutes work.

 

[jwilson]

The only way to stop rust coming back is grind the rust back to bare metal and use two coats of zinc rich epoxy, ensure humidity is low otherwise you risk flash rusting. Rust converters don't work I tried them on our steel boat and the rust always comes back.

I agree that rust always comes back, but in practice a splash of Fertan or similar rust converter, then a coat of a zinc primer, then antifoul, is simple, quick and holds most rusting off for another year. As you usually can't get at the very bottom of an iron keel for long each year it's almost impossible to fully protect the bottoms of keels so even if you try the epoxy it probably won't last much longer and you'll be back with rust next year.

There's a difference between dealing with rust on a steel hull or deck, and the bottom of an iron keel. And remember keels are fat chunks of cast iron, a very different material in many ways to thin sheets of steel.

 

[Quandary]

I have found that minimum three coats (preferably 5, it dries fast) of Jotun Vinylester 88 primer was effective, International's Primocon is almost as good and not that much more expensive, if any small patches show rust again next year abrade and paint again locally, after about thee years you will have it beaten. Using a rust convertor would do no harm and might reduce the rubbing down needed.
Primocon used to be a lot more effective when it had so much bitumen in it that it leached through the antifouling.

 

[duncan99210]

The only way to stop rust coming back is grind the rust back to bare metal and use two coats of zinc rich epoxy, ensure humidity is low otherwise you risk flash rusting. Rust converters don't work I tried them on our steel boat and the rust always comes back.

+1 Works well for me, but the boat's in Greece, so working on her in May/June there are no problems with flash rusting. Good epoxy primer is well worth the extra cost.

 

[lpdsn]

My keel was properly treated but the next year she was lifted out when I wasn't around and over enthusiastic pressure washing chipped it off a few areas. Had clearly worked as still bare metal when I turn up a couple of days later but I didn't want to be doing it every season.

As a short-term measure rather than redoing the lot, I sanded the patches till they had smooth edges, used spray-on etch primer, then epoxied over that, Primacon'd then anti-fouled. It has, surprisingly, been fine for four years now. So worth considering etch primer as a cheap alternative if you don't want to invest in a full treatment.

 

[lpdsn]

International's Primocon is almost as good and not that much more expensive,

I don't know what Primocon used to be like, but tried 5 coats of it in 2009 after getting back to bare metal and it was pretty near useless.

 

[roblpm]

I don't know what Primocon used to be like, but tried 5 coats of it in 2009 after getting back to bare metal and it was pretty near useless.

I have done fertan. Multiple coats of primocon. Then antifouling. This has kept the rust at bay. But needs doing every year.

 

[Spyro]

I just zap the rust spots with a flap wheel on my angle grinder, immediate rust converter and then underwater primer and AF. Each year a few spots come back but on 10 minutes work.

+1 apart from using a steel brush on the angle grinder.

 

[Seajet]

I have tried every paint and steel treatment on my 3/4" galvanised steel lift keel over the last 39 years.

THE one treatment which stands out head and shoulders above the rest is

Dulux Metalshield, it's brilliant stuff.

One part, but requires the one part Metalshield undercoat.

Available from Brewers, £ 29.00 for each 750 ml tin, but worth it - on a well prepared steel, iron or alloy surface - in /or v close to Langstone Harbour.

As for antifoul, last season my usual Cruiser Uno was useless, so I and most people I know are switching to Seajet a/f.

 

[TQA]

A needle gun is better than grinding.

Rust converters do work, I use Ospho.

A 2 part zinc rich epoxy primer is what the oil industry use so that was my choice.

I cruised a 25 year old steel boat for many years.

 

[Seajet]

I tried zinc rich Galvafroid - sometimes labelled ' Admiralty Steel Treatment ' or something like that - it feels like it should be good but it's too soft, didn't last well in my experience.

I've also tried Fertan, Primocon, 709 epoxy ( a big mistake as any chip in the layer will trap water against the keel - normally the lift keel gets some relief on a half tide mooring ) in fact everything I've ever heard of - I temped at a chandlery for a while and tried every treatment they had, not much success.

Then a few years ago I heard about ' Metalshield ' ( don't let ' Dulux ' put you off, this is industrial stuff ) and was amazed, first time ever the keel looked the same on autumn lift out as when I painted in the spring.

 

[oldharry]

Do you use a rust converter under the Metalshield?

 

[vyv_cox]

A needle gun is better than grinding.

Needle guns are great on steel, they are used on offshore platforms where grit blasting is not possible. They are very poor on cast iron, driving rust and graphite into the surface layers.

 

[Seajet]

Old Harry,

no, there's no rust, I'm just keen to keep it that way !

NB this is the second keel, we're very fortunate ( if not unique even among much newer boats ) in having a supply of galvanised steel keels and cast iron ballast bulbs from the original foundry.

The original keel did rust to a dodgy degree after about 25 years; this was mainly because I didn't have the brains to winter the boat on high trestles - allowing access and maintainence - for the first 5-10 years.

I tried rust converters on that, didn't help at all.

Now as I run the owner's association I warn everyone to look after the keels, and give out the simple plans for the high trestles.

Of course the need for inspection and maintainence applies to all lift keelers, not just Andersons - I once met a chap in Yarmouth with a young family on a Sailfish 18, cheerfully setting off for Cornwall, ' Oh the keel dropped out on the way here ' - when I said in my best Sergeant Wilson ' I say, do you think that's terribly wise ? ' - he became very uppity !

 

[PeteCooper]

A couple of years ago I contacted Dulux having seen Metalshield recommended on here. and here is their reply:

"We not recommend Dulux Trade Metalshield for using on a boat, we would not have a product that I could recommend."

Perhaps I should have asked why not but I didn't - it was enough to put me off.

I used Primocon and I reckon if you follow the instructions carefully and get it on as soon as you can after you have gone back to bare metal it is as good as anything.

 

[GHA]

Rust converters do work, I use Ospho.

For those in the UK phosphoric acid is available in Wickes but looks like they might be phasing it out so stock up -

http://www.wickes.co.uk/Wickes-Grout-Film-Remover-1L/p/166088

i usually get as close to bare metal as possible, coat of acid, good wash, another coat of acid followed by another really good wash then dry with a blow torch followed by amerlok sealer which is designed for applications where abrasive blasting is not possible. Plus whatever epoxy paint is available ontop of that.

Though probably pointless and completely over the top for a cast iron keel quite likely to be riddled with impurities

https://books.google.co.uk/books?id...page&q=boat cast iron keel impurities&f=false

 

[Seajet]

A couple of years ago I contacted Dulux having seen Metalshield recommended on here. and here is their reply:

"We not recommend Dulux Trade Metalshield for using on a boat, we would not have a product that I could recommend."

Perhaps I should have asked why not but I didn't - it was enough to put me off.

I used Primocon and I reckon if you follow the instructions carefully and get it on as soon as you can after you have gone back to bare metal it is as good as anything.

it would be interesting to hear the reasoning of that Dulux bod, as it was recommended to me by an independent paint expert, an ex lecturer on the subject; sadly I can't ask him further as he is no longer with us.

I can say from personal experience Metalshield works brilliantly, I've used it for at least 5 years now; if you think of the most extravagant claims ' Hammerite ' ( which I also tried - useless ) makes, Metalshield actually lives up to such performance and more...

I have no connection with it or Dulux, but when I come across something so good I do try to mention it.

I and my father are trained engineers and know preparation is key, but even with that I found Primocon very poor in comparison.

 

[vyv_cox]

Must say I agree about the Primocon. I brought my steel rudder home, ground it clean with angle grinder and flap discs, applied five coats of Primocon and the rust was showing through before the boat was launched. The paint is very viscous and does not flow well, so I assume there are pinholes even through multiple coats.