What Causes Rust in Metals

Rust is an all-too-common phenomenon. Whether it is an old gate crumbling away or a car in the junkyard, we all see rust on a regular basis and know it is the result of a metal item not being well cared for. It can be found on a wide range of metal surfaces, from car bodies to metal tools, and can cause structural damage and aesthetic issues if left unchecked. Have you ever wondered why it happens though? What causes metal to rust in the first place?

Understanding how rust works is essential for maintaining the longevity and value of your metal structures, like bridges and boats. At its chemical level, rust occurs when metal is exposed to moisture and oxygen. The chemical reaction that causes rust is a form of corrosion that slowly eats away at the rusted metal surface, over time leading to:

• Weakness
• Discoloration
• Deterioration

In this blog, we will explore the causes and effects of rusted metal, as well as the rust prevention measures that should be taken to prevent it. 

What Causes Rust on Metal?

Rust is a type of corrosion that occurs on metal surfaces when iron reacts with oxygen and water. The chemical reaction that causes rust is called oxidation. The oxidation process eats away at the metal and creates visible rust on the metal's surface. When metal is exposed to any type of moisture — even humidity in the air — the iron atoms in the metal react with the oxygen molecules in the air to form iron oxide, also known as rust.

The chemical reaction can be represented by the following equation:

iron + oxygen + water = iron oxide (rust)

Rust can occur on any iron-containing metal, including steel, iron, and cast iron. The rate at which rust forms on metal surfaces depends on the level of humidity, the amount of oxygen present, as well as the type of metal. 

The lifespan of an uncoated metal that is susceptible to rust is significantly shorter than one that is coated with a zinc-rich cold galvanizing compound made by ZRC. When left untreated, rust can fully corrode metal into a dry oxide powder. The result of a chemical reaction in the oxidation process is not something to risk!

ZRC Cold Galvanizing Compound for Rust Prevention

A cold galvanizing compound, or zinc-rich compound, has the characteristics of paint, but it's not a paint. The biggest difference is the percentage of zinc present in the corrosion prevention coating. You see, a lesser noble metal will corrode to the more noble. Zinc-rich compounds can be applied by spray or brush (like a paint) to steel. Zinc, being less noble than steel, forms hydroxycarbonate salt when it corrodes that bonds with the existing zinc in the film coating while upholding galvanic protection. This creates an advanced, self-healing film that ensures the metal surface beneath the coating stays protected. Because the percentage of zinc in ZRC is so high and the particles are not encapsulated, the corrosion protection is galvanic, like hot-dip galvanizing.

A cold galvanizing compound is a product that simulates the performance of hot-dip galvanizing. The difference is that hot-dip galvanizing needs to be applied in a controlled setting, like a manufacturing plant. Cold galvanizing compounds can be applied on-site directly out of a can, similar to paint.

Application Options for Rust Prevention 

Once applied and dried, ZRC® Cold Galvanizing Compounds are designed to perform to the same high-level industry standard of corrosion prevention whether sprayed-on or applied by brush. We have a number of different products, each specifically designed for certain use cases. Our blog, Choosing the Right ZRC Zinc Coating to Prevent Corrosion, includes everything you need to know in order to select the right ZRC product. Beyond selecting the exact ZRC product, you have two application options:

Brush-on Rust Prevention

Our cold galvanizing paint was the original ZRC product, and is still the industry standard. It is equivalent in function yet superior in convenience to hot-dip galvanizing. Our experts recommend the brush-on applications when you’re undergoing a high-volume project, like steel girder I beams. If you have a big job ahead, we recommend liquid paint. This is because you will get more coverage from a gallon of cold galvanizing paint than a spray can.

Spray-on Rust Prevention

Cold galvanizing spray can be administered in aerosol form or using a compressor or airless spray techniques. ZRC's Cold Galvanizing Compound in aerosol yields the same superior performance as the brush-on type. ZRC simply adds propellants and other ingredients so it sprays easily and evenly out of an aerosol can. ZRC Worldwide's aerosol application method is low in VOC and yields a consistent dry film thickness not found in low-cost solutions. Once applied and dried, zinc-rich coatings are designed to perform to the same industry standard of corrosion prevention. This is true whether sprayed-on or applied by brush. They perform the same once applied!

This application option is sought after for a number of different reasons. Let’s say you need to climb a ladder to apply the product. Would you rather bring a 5-gallon bucket of paint or a 12-oz spray can? Putting a spray can in your tool belt is clearly the easier mode of application. This is just one of the reasons people choose cold galvanizing spray.

Zinc in Action

Rust prevention is crucial for any type of commercial metal, as unchecked corrosion will eventually cause significant damage to the structural integrity of the metal and compromise its integrity over time. Cold galvanizing compounds are coatings utilized to create a protective barrier against rust and corrosion on metal surfaces like bridges, cell towers, boats, and other marine structures. These compounds contain zinc particles that are suspended in a liquid carrier, in this case paint. When applied to a metal surface, the zinc particles adhere to the surface and form a protective layer that acts as a “sacrificial anode.”

A sacrificial anode is a metal that is more reactive than the metal it is protecting. In the case of cold galvanizing compounds, the zinc takes on this role and corrodes instead of the metal surface of your gate, bridge, or other metal structure. When these zinc particles corrode, they create a passive layer on the surface of the metal which prevents further corrosion and protects  your steel from corrosion. The result? Aa reliable solution to safeguarding metal surfaces from rust and corrosion.

Use ZRC Products to Combat Corrosion Before You Have Rusted Metal

There are many products that service the varying needs of the corrosion prevention industry. Imitation is flattering, but the proof is in the paint. ZRC Worldwide created zinc coating technology as a hot-dip alternative to combat corrosion and has been a worldwide leader in the space for almost 70 years.

Using a ZRC product ensures you achieve a strong bond between the zinc and the metal that is being protected. Whether touching up an existing project or completing a full-sized job from scratch, our team will ensure you get the right product and the correct application method for your needs.