Cast iron kettle used as fountain: corrosion, suggestions for finishes and care

Q. We own two 200+ yr-old sugar kettles (as they were called in the sugar industry in Louisiana) from a plantation formerly owned by my wife's family. One is 5', the other about 33". Both have been used to grow water lilies and goldfish for the past 27 years. Both had been treated for rust and painted with Rust-Oleum primer and black paint before being filled. All that is long gone.

I emptied the smaller kettle and found the it to be deeply etched with rust. A good deal comes off with a steel wire brush, but it just keeps coming. The kettle was resting on dirt, and its underside heavily blistered with rust. I expect the large kettle to be in similar condition when I drain it.

I'm looking for advice on how to care for the two kettles.
The earlier discussion on this thread, while dating from the mid-2010s, is the closest I have found to useful information.

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Q. I am turning 200 gallon cast iron kettles into fountains. I want to put a "finish" on for the pool of water to aid in the ability for water clarity. I have used an automobile primer & a black epoxy type finish so far, but the epoxy is pulling away, & splitting from the side wall of the kettle underwater. The best I can tell, is that my primer, & epoxy finish are not agreeing w/ each other. I want a black finish, but would also like a solution that can have at least a 5 year underwater life. Thank you for any advice in advance.

A. Problems with the pretreatment, the paints, or both.
Cast iron is somewhat porous, especially if weathered. Preferred pretreatment is abrasive blasting, metal prep with Picklex® [affil links]® (International Chemical Products), rinsing and moisture bake-out. Paint when kettle cools below 100 °F or per paint instructions. If without an electric oven capable of handling a kettle, skip the liquid steps.

Automotive primers are cheap, easy to apply and sandable, but not fit for immersion applications. Use the marine paints that boatyards use on cast iron keels, or that waterworks use on piping & tanks expected to last 50+ years. As you may have weathered kettles with some dampness, use Amerlock Sealer (clear, penetrating epoxy, 100% solids cured) and then Amerlock 400, or equivalents. Top with a glossy polyurethane if desired. Properly applied, should pass these tests:
Salt spray per ASTM B117 for 3000 hours -- Face blistering: None
Immersion per NACE TM0169 in fresh water for 1 year -- Blistering: None

Ken Vlach [deceased]
- Goleta, California
Finishing.com honored Ken for his countless carefully researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at finishing.com, continue to benefit from.
2006