Why is My Chimney Rusting?

The chimney is one of the most visible features of a home. While brick chimneys are durable structures built to withstand a crackling fire in the fireplace, they are not indestructible. The chimney comprises several different components, some of which are metal. These components, including the damper, smoke shelf, and flashing, are susceptible to rusting. 

What is Rust

Ferric or Iron Oxide is a corrosive, inorganic compound that is more commonly referred to as rust. It is sometimes confused with ferrous oxide, an entirely different compound. In simplest terms, rust develops when water droplets mixed with oxygen and carbon dioxide (or other oxides) encounter ferrous metal materials such as iron or steel. The degree of oxidation depends on the amount of iron that is present in the metal and the level of oxides in the atmosphere. Since saltwater significantly accelerates oxidation, chimneys in coastal areas are more prone to rust. Humid climates also provide suitable conditions for rust.

Signs of Rusting

When rust develops, it discolors surfaces with a reddish-orange stain. Homeowners may often spot rust stains along the exterior of the chimney. It can occur when a metal chimney cap is rusting. There may also be reddish-orange rust stains along the bottom of the chimney due to the presence of iron and other oxides in the municipal water supply when watering the lawn. 

The problem with rust is that it is a part of corrosion, which can be very destructive to the chimney, including non-metal materials like clay flue tiles and brick and mortar. The rust will continue to damage the surface until it is repaired or replaced. For instance, the flashing is a metal strip that seals the gap where the chimney meets the roof. When the flashing corrodes and rusts, the seal weakens, allowing water to leak inside, resulting in further chimney damage.

Also, the combustion process that occurs when lighting the fireplace produces several oxides, including carbon dioxide, nitrogen oxide, and sulfur dioxide. The residue from these chemicals sticks to the walls and metal components in the chimney, and when it oxidizes, it exposes the flue to corrosion and rust.

How to Remove Rust Stains

Fortunately, there is an easy solution to removing rust stains from brick chimneys. Saver Systems offers a professional strength Brick and Mortar Cleaner that removes many different types of chimney stains, including rust, creosote, mildew, and algae. It is applied directly to the brick and mortar surface.  It can also remove rust from concrete surfaces and is safer than using muriatic acid to remove rust stains. 

Preventing Chimney Rust

The key to preventing chimney rust is minimizing exposure to moisture. Inspect and clean the chimney annually and make timely repairs to protect against moisture intrusion. Another way to avoid rust is to replace rusted or corroded exterior components that are exposed to the weather, like the chimney cap and flashing, with stainless steel components.  Also, non-ferrous metals do not rust, but they are still susceptible to corrosion. These metals include bronze and copper, and many homeowners have installed these types of chimney caps.  Instead, use stainless steel components when possible. Stainless steel contains chromium making it more durable than other types of metals and gives it its distinguished shiny appearance. It may be costlier, but it is more rust-resistant. A stainless-steel flue liner is also more durable and less expensive to maintain than a clay tile liner.