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What Bolts are Best for Outdoor Use?
Stainless steel bolts are popular choice for outdoor use overall. They balance structural properties, corrosion resistance and price. The chromium added to the steel mix reacts with the oxygen in the air and forms a protective outer layer during its creation. This makes stainless steel extremely resistant to corrosion and rust whilst maintaining robust structural properties, but they come at a higher price.
Galvanized bolts are also popular depending on the outdoor setting as they are generally cheaper.
Which is stronger stainless steel or galvanised steel?
The vast majority of galvanised steel bolts are Class 4.6 and stainless steel mostly A4-70 and A2-70 (304 and 316 stainless steel respectively). This means stainless steel is generally stronger. Bolts Nuts Screws Online only stocks bolts with the appropriate head marking to verify.
However there is a version of a galvanised bolt referred to as a structural assembly; these are high-strength, usually 8.8, which is slightly stronger than stainless steel. It is primarily used in heavy structural applications, such as bridges, large sheds (similar to Bunnings), high-rise towers, and heavy steel structures. Usually ordered by structural engineers.
Key factors in choosing the best outdoor bolt include:
- Exposure to weather and moisture
- Corrosion resistance
- Load and structural requirements
- Compatibility with materials
- Look and feel
- Cost
The combination of moisture and salt content in the outdoor air, especially in coastal regions, marine environments and along waterways can have a particularly corrosive effect on metal exposed to the elements.
If high corrosion resistance outdoors is a requirement then stainless steel bolts are a must.
Galvanized and stainless steel bolts do not have the same structural properties; stainless steel is generally stronger, more durable, galvanized steel is more pliable and is typically chosen when extreme strength or corrosion resistance isn't paramount.
Different outdoor application for bolts
Galvanised bolts can be used in outdoor settings where standard corrosion resistance and structural integrity is needed such as
- bridges,
- steel framed buildings,
- communications towers
- water pipes
- shade sail areas
such as for council applications, so long as the structures don’t occur near beaches and salt water environments.
Stainless steel bolts, due to their extreme corrosion resistance and durability are used in high salt and humidity areas such as
- jetties and pontoons
- wooden decking
- fencing and balustrading
- pergolas
- swimming pool areas
When used in wooden fencing, decking and timber framing, galvanized steel can be corroded by the chemicals used to treat the wood. In turn the galvanized steel can eventually rust and go bad leading to degradation of the wooden structure around the bolt. This is especially prevalent in higher humidity and salty climates and areas such as coastal regions.
Which is cheaper?
Galvanized bolts are generally cheaper than stainless steel.
Do galvanised and stainless steel look the same?
Stainless steel is more aesthetically pleasing. It has a higher shine and can be polished to create a highly reflective and attractive surface in an outdoor application.
Which are best, stainless steel or galvanized bolts for outdoor use?
Outdoor bolts that won’t rust include both stainless steel and galvanized steel.
The choice depends on the application and budget. Both have corrosion resistance and structural properties and where cost is a factor galvanized is generally chosen. If high corrosion resistance and superior tensile strength is required then stainless steel bolts are the way to go. Structural assembly (galvanised high strength steel) is used where corrosion resistance and ultimate structural property is required.