Water boiling over on cast iron steamers can create rust and mineral stains on the steamer and on the wood stove surface it sits on. Credit: Courtesy of Sarah Sycamore Thompson

When Sarah Sycamore Thompson noticed the cast iron humidifier on top of her wood stove was rusting and building up mineral deposits, she was at a loss on how to clean it up.

Turns out, she’s not alone.

There are plenty of homeowners around the state heating with wood who’ve started adding some moisture to the dry inside air by using stovetop cast iron steamers. Those steamers are great at humidifying the air, but they also are pretty good at rusting and discoloring.

Thompson posted a photo of her rusted steamer to a local social media homesteading group and soon others shared their own stories and photos of rusted cast iron steamers.

One of those was George Hofgren of Fairfield, who has used wood heat for years and knows a thing or two about cast iron maintenance,

“You have hot water and you have material that wants to rust,” Hofgren, a long-time user of wood heat and cast iron stoves. “Once it starts to rust, it’s a growth process that happens in the metal, not on the metal.”

That means the best way to clean a cast iron stove top steamer is to take preventative action to keep any rust from getting a foothold in the first place.

Hofgren suggests treating non-rusted old or new clean cast iron with a commercially sold stove polish, also known as stove black.

“Stove black is basically a polish with wax and carbon in it,” Hofgren said. “You want to rub that into your cast iron and, once it heats up, the wax burns off and it will leave behind a nice carbon black finish.”

Stove polish is usually found anywhere that sells or services wood-burning stoves.

If the steamer — or portion of the cast iron stove the steamer normally sits on — rusts, Hofgren said more drastic measures are needed.

“You need to remove the rust mechanically,” he said. “There is no washing it off.”

He said a stiff wire brush or coarse sandpaper can get any surface rust off. But to get any rust growing into the metal removed, the only option is having it sandblasted.

Sandblasting — also called abrasive cleaning — uses compressed air pressure to shoot a stream of sand or other tiny particles against a surface to remove any dirt or contamination.

“You need to get the rust off by any means,” Hofgren said. “You could take it to a shop like an auto body shop and see if they could sandblast it for you.”

Once rust-free, Hofgren said the steamer and wood stove should be polished once a year. And anytime you notice a drip of water on a surface, wipe it up.

“You don’t want to let water sit,” he said. “It will just penetrate into the metal and rust.”

Water poses another problem for cast iron, Hofgren said. Here in Maine, the groundwater is hard, meaning it has a high mineral content. So not only is water on a cast iron steamer potentially creating rust, it can also leave behind whitish stains due to mineral build-up on the steamer’s surface.

Over time, those stains and deposits can make the outside of a steamer look pretty grungy.

Lemon juice or vinegar can be used to clean off the deposits. You can also make a paste out of baking soda and water. Spread the paste on the cast iron, let it sit for a few minutes and then wipe it down. Whichever method used, just make sure you thoroughly dry the steamer when done.

Rust and mineral-laden water get on the outside of a cast iron steamer when it boils and bubbles over. To prevent that, simply do not overfill it.

Hofgren has one final suggestion.

“If you want a steamer that is decorative and won’t rust, get the enamel version, if available,” he said.

Correction: An earlier version of this story incorrectly spelled George Hofgren’s last name.

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Julia Bayly

Julia Bayly is a reporter at the Bangor Daily News with a regular bi-weekly column. Julia has been a freelance travel writer/photographer since 2000.