When to Use Stainless Steel Vs. Galvanized Zinc Screws for Outside Construction

When you’re planning some kind of outdoor structure, such as a deck, you might not usually stop and wonder whether you should use screws that are stainless steel or ones that are made of galvanized zinc. However, this is actually a very important point to consider before you buy your materials and get started on the job. 

Galvanized screws are often an attractive choice because they’re cheaper – nearly half the price of stainless steel. Price is not the only factor, however. Let’s look at it from a few other angles before you make the choice.

  •   What is the difference?

First of all, what is the difference between these two different types of fasteners? Galvanized screws are basically just black steel with a coating of zinc. Zinc is an extremely tough protector, but it is possible to wear it down, creating a weak spot through which the original steel is exposed to the elements. Black steel can start to rust quickly once exposed.

In contrast, stainless steel does not need to rely on a coating to toughen and protect it. It is an alloy that includes a significant quantity of chromium. The presence of this tough metallic element improves the durability of the steel and adds rust-resistant qualities as well. The most important point is that stainless steel has its name because it is just that – entirely stainless, by its chemical composition, throughout. A fastener that is made of the material is stainless from its thread to its core, from its head to its point and everywhere in between. Galvanized fasteners, on the other hand, rely on their zinc coating for their rust resistance. This difference is the main factor in your choice between the two – but it isn’t the only one.

  • Strength and Rust Resistance

A galvanized screw seems very strong to begin with – every bit as strong as stainless steel, surely. The problem is that this strength might only be skin deep, so to speak. Under that thin layer of hard-wearing zinc is plain black steel that is very susceptible to rust and corrosion. Now, that’s fine provided the zinc coating is never worn away somehow. Over time, however, this coating can be worn away, even if only in one small spot, leaving the rough steel underneath open to the elements. With stainless steel, however, especially of 316 grade, this vulnerability is almost completely eliminated.

There is more to the question of strength and durability than a material’s ability to resist rust, however. The chemical make-up of stainless steel, which gives it that power to withstand rust and corrosion, also gives it a strength and hardness with which galvanized steel cannot compete. Stainless steel screws have an incredibly high tensile strength, measuring between 100,000 and 150,000 tensile pounds per square inch (PSI). Screws made from galvanized steel, on the other hand, have an average of only 62,000 PSI. When it comes to strength and durability, therefore, stainless steel always comes out on top. Having said that, you may not necessarily need that high tensile strength for your particular project, and galvanized screws are perfectly capable of resisting rust so long as the coating remains intact. You may, therefore, decide to go with galvanized to keep costs down or because their look is more suitable.

  • Appearance

This is not really a direct contest. Galvanized fasteners have that hardy, dull, industrial look, while stainless steel is shinier and more refined looking. Which one of the two you choose depends on your preference as well as the overall look and feel of whatever it is you’re building.

So, galvanized wins when it comes to price, stainless steel when it comes to strength and rust protection. They come out fairly even in the looks department. You would need to decide which of the factors are more important to you. If you go for the savings, hopefully, you’re careful with your zinc fasteners and are building where exposure to moisture and corrosives won’t be that much of a problem. Stainless steel is certainly the safer option, provided that you’re willing to spend a little more.

It all comes down to the specifics of your project. Contact Marsh Fasteners; we will be able to advise which screw is best for the job.

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