Does Cast Iron Rust Outside?

Cast iron is susceptible to rust over time when exposed to moisture. The metal is porous and will absorb moisture, leading the surface of the iron to turn into rust. However, regular maintenance of cast iron cookware helps prevent rust accumulation on the metal. With that being said, does cast iron rust outside?

Yes, cast iron can rust if left outside and exposed to moisture. In the presence of water and oxygen, rust can occur on metal. If you leave your item made of cast iron outside, it can rust. If your cast iron item is not protected against rust, then it will definitely rust.

However, cast iron will not rust when left outdoors with protective measures unless it is left in a consistently wet environment that does not allow water to drain or dry. If moisture or water is left standing around the base of the cooker, it will eventually rust.

This article has information on cast iron, what makes it rust, and how to protect it from rust when it is outdoors.

About Cast Iron

Cast iron is a kind of metal that is stiff and not malleable. This explains why it is the most suitable material for garden planters and other heavy equipment.

About Cast Iron

Unlike some of them, the process of making a piece of equipment with cast iron involves molding the shape of the equipment you want to make, melting the metal, and pouring it into the mold. After this, you can then file or saw the cast iron into the shape of the item you are making.

How To Protect Cast Iron Outside

Items like planters that are made of cast iron are used outside. And these items are not items you take into the house at the end of the day. Knowing that keeping your cast iron item outside may be inevitable in some situations, you would want to know how to protect your item when it is outside.

How To Protect Cast Iron Outside

Leaving your cast iron item outside means you are leaving it at the mercy of corrosion. However, there is a lot you can do to ensure that it does not rust. To protect it outside, you have to seal it. Paints and sealants are essential for protecting the cast iron finish from corrosion. With sealant or paint lining the surface of the cast iron item, if water or moisture falls on it, it will not penetrate the cast iron finish itself. Here are some tips to guide you on sealing or painting your cast iron item:

  • Before you start applying the sealants to your cast iron item, rid it of every dirt, dust, or grease. To do this, you should use a cleanser that is not too harsh. Dishwashing detergent is fine. Or any other non-abrasive option. If there is dirt on the cast iron item, the sealant will not adhere properly.
  • De-rust the cast iron item to allow sealant and paint to stay on it. Use steel wool to wipe the surface to rid it of light rust. However, if the rust is heavier than what steel wool can clean, use sandpaper to wipe the rust off the item’s surface. Using sandpaper with medium-grit is advisable because something too harsh for the item will scratch the surface. Scratches on the surface of your cast iron item will affect its aesthetics.
  • Prime the surface of the item to allow it to take the paint better. Primers are essential for preparing the surface of any metal to take any other coating. You can apply primer on the surface of your cast iron item using a brush or by spraying it. After applying the primer, leave it to dry as recommended by the producer. The manufacturer’s recommended drying time may be long or fast. It is advisable to follow the recommendation to get the best result.
  • Paint the cast-iron item with the color of your choice. When choosing a paint, go for one that is made for metals. This will give you maximum effect. You can apply the paint using a brush or sprayer. When painting the metal surface, ensure that you cover every area of the item. Look out for hidden areas and crevices. Do not apply the paint too thin or too thick. Leave the paint to dry up completely.
  • Apply sealant to the metal. After applying the paint and leaving it to dry, you will apply a sealant to the metal surface. Then leave it to dry. Like the primer, following the manufacturer’s recommendation is essential for getting the best result. Depending on the manufacturer’s recommendation, you can be looking at a few hours or more, say up to four.
  • To protect the finish from conditions and elements like rain, sunshine, or snow and to let the finish stay long, apply automotive wax to the cast iron item surface. You can apply the wax using a microfiber cloth. Ensure to follow the manufacturer’s instructions during the application.
  • Ensure that you repeat the wax coating on the cast-iron item from time to time. This will help the paint and finish to stay longer. The cast iron item will be exposed to the elements if they wear off. If the paint and sealant wear off, the metal item will be exposed to corrosion.
  • Keep the cast iron item appropriately. Ensure that you do not expose it to moisture and water. Keep the item in an area where direct rain and sun will not get to it easily. It is advisable to keep your items indoors as much as possible. During cold months of winter, this is most essential. If your cast iron item must be outdoor, ensure that you cover it when it is not in use. If cast-iron items are left outdoors, they can rust due to exposure to water and moisture. Ensure that you place the item on a flat and solid surface. Avoid placing items on watery surfaces or places with standing water.


Cast iron can rust when left outdoors if it is exposed to elements like rain. If you must keep your cast iron item outdoors, keep it in a dry place and cover it when it is not in use. Painting your item and coating it with sealant is essential to keep it from rust.

Evan Cooper

Evan Cooper

Hi, I’m Evan Cooper, the founder and an editor of this site, Doesitrust. I’m a chemical engineer and working in a rust-eliminating paint manufacturing company. Besides this profession, I’m a researcher and blogger.

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