Steel CB protection

[johngsandusky]

I've had two boats with iron keels. Both were primed and painted originally and held up well. On one I scraped scaled and sanded it by hand, primed with zinc paint, and copper bottom painted. That was over 20 years ago, it still looks good. I have no doubt that galvanizing is best, but many thousands of steel ships travel the world with no more than paint and primer on the hull. Many many classic boats have iron keels that are just painted too.

[Peerie Maa]

I have no doubt that galvanizing is best, but many thousands of steel ships travel the world with no more than paint and primer on the hull. Many many classic boats have iron keels that are just painted too.

Cast iron ballast keels and mild steel corrode at vastly different rates.

[MN Dave]

Don't forget the zinc anodes or impressed current systems on those thousands of ships:

I have no doubt that galvanizing is best, but many thousands of steel ships travel the world with no more than paint and primer on the hull. Many many classic boats have iron keels that are just painted too.

Cast iron ballast keels and mild steel corrode at vastly different rates.

This links to a pdf that has the results of testing done on zinc rich primers, followed by tests on rust converters.

Zinc rich paints:
1. Zinga Organic epoxy primer 96% Zn
2. Zinc Clad IV Solvent-based 85% Zn
3. Zinc Clad XI Water-based inorganic Zn silicate with no VOC and 90% Zn
4. N-5751M2 Solvent-based moisture cure 90% Zn
5. Intershield 300V Aluminum-rich epoxy
6. Epoxzen Organic epoxy with 90% Zn

Rust converters:
1. Gempler’s (water-based, tannic acid)
2. Loctite rust treatment (polymeric-based, barium sulfate)
3. Total Solutions (water-based, tannic acid)
4. Phoscote (phosphoric acid – current USMC product) <>>
5. VpCI CorrVerter (combined rust converter and primer)
6. Corroseal (water-based, tannic acid with primer)
7. Gem Rust Killer (under test)
The rust converters were coated with a non-corrosion inhibiting epoxy primer and a polyurethane topcoat. While they are good paints, there was no chance that the rust converters would look good in these tests. It is unfortunate that they didn't compare to a sample without a converter. All I can say is that none of the rust converters looks bad, since all they do is help the paint stick to the metal.