Iron keel rust

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andylipsberg

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Hi there,

I have small patch of rust on the keel 15 cm or so. It's barely visible, but I suspect there was a previous repair and the area has rust stains.

Would it be the right fix:
  1. Grind it to the metal
  2. Underwater primer (any suggestion of brand, how many coats?)
  3. Then antifouling
 
International Primocon or Hemplel Underwater 3 coats. There are other primers, but they are readily available in small tins whereas others tend to be in 2.5l.
 
Thanks for the replies. I'm getting mixed proposals on what has to be done, so I'm getting more confused with every person I speak.

I currently have International Hard antifouling on the hull. The hull is in pretty good condition.
  • the yard is suggesting just to repaint even without sanding with seahorse antifouling, rust on keel is cosmetic in their point of view, nothing to be done.
  • broker suggested soda blasting the keel (which is overkill) converter, epoxy, prime, antifoul
to my understanding I can patch repair the keep with rust converter, primer and antifouling or maybe nothing to be done since it's just a rusty stain on the keel nothing is eroding or bubbling.

lightly sand the hull and repaint with same international hard antifouling.
or should I still apply the primer before new antifouling layer?
 
Well, you will get as many opinions as people. I think a rust converter would do too. You need to read its instruction to find out if you can cover it directly with antifouling. I have a similar problem too, and was thinking about using Bonda Rust Primer | Rustins - apparently, you can apply antifoul right away.
But will probably leave it as I store my boat ashore and will see how it looks after the season.

Why broker is involved?
 
slawosz said:
Well, you will get as many opinions as people. I think a rust converter would do too. You need to read its instruction to find out if you can cover it directly with antifouling. I have a similar problem too, and was thinking about using Bonda Rust Primer | Rustins - apparently, you can apply antifoul right away.
But will probably leave it as I store my boat ashore and will see how it looks after the season.

Why broker is involved?
Click to expand...
I bought the boat through the broker. But I don’t fully take any of these opinions as none of those people are truly interested. One wants to finish the deal, yard just wants to put a boat in the water. That’s what they only do.

i watched on youtube

the whole process is well explained, but this bottom was in bad condition, not a seasonal thing.
 
My opinion - the full gritblast treatment is only needed if you are going to fair the keel, which can be beneficial for keels cast horizontally. Or if you are going to a/f with Coppercoat, which needs a very good substrate to stay attached for 10+ years.

Otherwise for conventional a/f, do as Tranona suggests, clean up, prime the rusty bits and antifoul it. You will need to patch up future overwinters perhaps but only small areas, no hassle. Appearance is inconsequential.
 
andylipsberg said:
Hi there,

I have small patch of rust on the keel 15 cm or so. It's barely visible, but I suspect there was a previous repair and the area has rust stains.

Would it be the right fix:
  1. Grind it to the metal
  2. Underwater primer (any suggestion of brand, how many coats?)
  3. Then antifouling
Click to expand...
  • Grind it to the metal
  • if the keel is cast iron use Fertan Rust Converter. Cast Iron is porous so even it you think you've ground out the rust there will be small pits hiding it. This product was recommended by a professional whist I was working on my keel ready to copper coat it.
  • Underwater primer
  • Then antifouling
 
I've also just done my keel, after putting it off for years - cleaned the rust off with a Tercoo Blaster(excellent tool but hard work and messy, but much cheaper thans Sand/Soda blasting...) Fertan rust converter, Primocon Primer, Shogun 033 antifouling. Looks good and hopefully should last.
 
I can't resist posting, as I do on all these threads, my scepticism around the Fertan - Primocon - AF coating schedule for anything but small area repairs.

Fertan is fine, but it leaves behind a residue that must be completely removed before coating (the 'just rinse with water' instructions would've left behind lots of contamination in the instances I've used it). Simple diluted phosphoric acid should work just as well.

Primocon and other vinyl-based primers only offer reasonable water resistance. They are not formulated to create a moisture barrier or protect bare metal in an immersive environment. My understanding is that a two component coating is required for this. Our keel (1989) came coated and faired with epoxy from the factory. Replacing that with a few coats of vinyl primer, sold for use as a tie coat, doesn't make sense to me.

I'm not saying that I would recommend the OP do any different than 'cure, prime, antifoul' for their small area...

But a while back someone came up to me in the yard, knowing we recently blasted and re-coated our keel, announcing that his research had turned up the ideal products for the job (the job being a bare-metal re-coat): Fertan and Primocon. My head was firmly in my hands at that point.

(For sake of disclosure, our re-coating scheme on a large keel too far gone for spot repairs was: professional blast; immediate coat with zinc phosphate epoxy primer, followed by numerous coats to use the rest of the 5l tin, followed by epoxy fairing compound, then a few coats of the same high build/aluminium additive epoxy primer the hull was having - because 'why not?' - and only then did it get a vinyl 'underwater primer', for its actual purposes of priming before antifoul)
 
dankilb said:
I can't resist posting, as I do on all these threads, my scepticism around the Fertan - Primocon - AF coating schedule for anything but small area repairs.

Fertan is fine, but it leaves behind a residue that must be completely removed before coating (the 'just rinse with water' instructions would've left behind lots of contamination in the instances I've used it). Simple diluted phosphoric acid should work just as well.
Click to expand...

You don't have to do any more than remove the surface dust from a surface treated with Fertan. The 'contamination' you speak of is the equivalent of a primer coat. OK it's a dirty brown colour but you should not remove it and it won't leach through a coat of primer. The instructions for the use of Fertan specifically say not to remove the coating. Perhaps had you followed the instructions your results would have been better.

Have a read through the patent printed on the Fertan site for a more thorough understanding of what is involved.

I would agree that there is little point in applying Fertan to a blasted clean, shiny metal surface. I would also agree that the full treatment you suggest is likely to give a superior result, it is however a very much more labour and cost intensive solution.
 
I respectfully disagree.

A dusty residue is not equivalent to a primer coat.

We did our keel to ISO blasting/decontamination standards, which would directly contradict the presence of Fertan anyway as you say. But it gives an idea of what paint needs to stick to cast iron under water!
 
I had mine back to bare metal but skipped the Fertan two seasons ago. Have just had to redo it all.

This time I used Fertan and five coats of Primocon. Everyone in the yard though it was overkill but I really don't want to all that again!
 
...but why not phosphoric acid? That's likely the active ingredient (the chemists will know). The difference is products like Fertan include other additives to make them safer, paint on easier, extend pot life, work in more applications, etc. etc.

Protecting metal underwater isn't easy. Ask the steel boat lot about Fertan and Primocon and see what they say. Definitely not 'overkill'.

I'd also ask why manufacturers bother epoxy coating their keels, if all you need is a few coats of single-pack primer? Our original epoxy coating lasted 30 years. I'm aiming to match that!
 
Slightly tongue in cheek, but how about Hammerite at the end of the season and anti foul at the start of the next one? ?
 
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