Can carriage bolts be used outdoors?

Can carriage bolts be used outdoors? That's a question I get asked a lot as a carriage bolts supplier. And the answer is, it depends. In this blog, I'll break down the factors you need to consider when deciding whether carriage bolts are suitable for outdoor use.

What Are Carriage Bolts?

Before we dive into the outdoor suitability, let's quickly go over what carriage bolts are. Carriage bolts, also known as coach bolts, have a round head with a square neck right below it. The square neck is designed to prevent the bolt from turning when you're tightening the nut on the other end. They come in various sizes and materials, and are commonly used in wood-to-wood or wood-to-metal connections. You can check out our Round Head Bolt With Square Neck for a closer look at the design.

Factors Affecting Outdoor Use

1. Material

The material of the carriage bolt is crucial when it comes to outdoor applications. Different materials have different levels of corrosion resistance, which is a major concern in outdoor environments.

• Steel: Steel carriage bolts are strong and commonly used. However, plain steel bolts will rust quickly when exposed to moisture, making them a poor choice for long - term outdoor use. But if you're looking for a more corrosion - resistant option, you can consider Zinc Plated Carriage Bolts. The zinc plating acts as a sacrificial layer, corroding in place of the steel to protect it.
• Stainless Steel: Stainless steel carriage bolts are a great option for outdoor use. They contain chromium, which forms a passive oxide layer on the surface. This layer protects the bolt from rust and corrosion, even in harsh outdoor conditions like near the ocean where there's salt in the air.

2. Coating

Even if you start with a good base material, the coating can add an extra layer of protection.

• Hot - Dip Galvanizing: This is a popular coating for outdoor bolts. In the hot - dip galvanizing process, the bolt is dipped in molten zinc, creating a thick, durable zinc layer. It provides excellent corrosion resistance and can last for many years in outdoor settings.
• Powder Coating: Powder coating can also be used on carriage bolts. It comes in a variety of colors and can offer good protection against scratches and corrosion. However, if the coating gets damaged, the underlying metal may be exposed to corrosion.

3. Environmental Conditions

The specific outdoor environment where the carriage bolts will be used matters a lot.

• Moisture and Humidity: High humidity or constant exposure to water can accelerate corrosion. For example, if you're using carriage bolts in a garden shed or a dock near a lake, the moisture can cause the bolts to rust over time.
• Salt Exposure: If the bolts are used in coastal areas, the salt in the air can be extremely corrosive. Stainless steel or heavily galvanized bolts are a must in these situations.
• Temperature Fluctuations: Extreme temperature changes can cause the materials to expand and contract, which may affect the integrity of the bolt and its connection.

4. Type of Connection

The way the carriage bolts are used in the connection also impacts their performance outdoors.

• Wood - to - Wood: When used in wood - to - wood connections, the wood can absorb moisture and transfer it to the bolt. This can lead to corrosion, especially if the wood is in direct contact with the ground. You may want to use Partially Threaded Carriage Bolts in these cases, as they can provide a better fit and reduce the risk of the wood splitting.
• Wood - to - Metal: In wood - to - metal connections, the difference in the expansion and contraction rates of wood and metal due to temperature changes can put stress on the bolt. Make sure the bolt is properly tightened and has enough clearance to accommodate these changes.

Advantages of Using Carriage Bolts Outdoors

• Easy Installation: Carriage bolts are relatively easy to install. The square neck prevents the bolt from turning, so you only need to use a wrench on the nut side. This can save time, especially when you're working on a large outdoor project.
• Aesthetic Appeal: The round head of the carriage bolt gives a clean, finished look. It can be a good choice for outdoor structures where appearance matters, like a wooden fence or a pergola.
• Strong Connection: Carriage bolts provide a strong and reliable connection. They can withstand a fair amount of shear and tensile forces, making them suitable for outdoor structures that need to be sturdy.

Disadvantages of Using Carriage Bolts Outdoors

• Corrosion Risk: As mentioned earlier, if the wrong material or coating is chosen, corrosion can be a big problem. Rust can weaken the bolt and compromise the integrity of the connection.
• Limited Adjustability: Once the carriage bolt is installed, it can be difficult to make adjustments. If you need to make changes to the structure later, you may have to remove and replace the bolt.

Conclusion

So, can carriage bolts be used outdoors? Yes, they can, but you need to choose the right material, coating, and consider the environmental conditions and type of connection. If you're planning an outdoor project, take the time to evaluate these factors.

If you're interested in purchasing carriage bolts for your outdoor project, I'd love to help. I'm a carriage bolts supplier, and I can provide you with high - quality products that meet your specific needs. Whether you need stainless steel bolts for a coastal project or zinc - plated bolts for a general outdoor use, I've got you covered. Contact me to start a procurement discussion and let's find the perfect carriage bolts for your job.

References

• ASM Handbook Committee. (2004). ASM Handbook Volume 13A: Corrosion: Fundamentals, Testing, and Protection. ASM International.
• Kennedy, J. B. (2009). Fasteners and Fixings. Newnes.