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

Updated on July 11, 2018
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Alistair has been working in home improvement for ten years.

Deciding whether to use stainless steel or hot-dipped galvanized screws can sometimes be more of an important decision that one might think.
Deciding whether to use stainless steel or hot-dipped galvanized screws can sometimes be more of an important decision that one might think.

Why Do I Have to Choose?

Before we get down to the underlying science, it is worth mentioning that both these technologies are fundamentally sound. They are both excellent choices for your home or business. This article is simply to help you choose which one is the better for you.

These two types of screw composition are sold in almost every single home-improvement retailer in the world, so it's not like you can necessarily ignore the topic altogether. There will come a time when you will walk down the screw and fastener aisle of Home Depot, Rural King, Lowe's, or your friendly neighborhood Ace Hardware, and when you do: both these types are right there vying for your attention. Which do you choose and why? Read on, dear mortal.

What Is Stainless Steel?

Let's start with what each is comprised of, and then onto which will suit your needs. First up is the stainless steel. This technology was first invented in 1913, as "rustless steel." Seeing as it's been around for over 100 years now, it's fair to say there have been hundreds of alterations to the formula over time. There's Ferritic stainless, Austenitic stainless, and Martenitic stainless. It's not super important to know each process or how they differ, but do know that it's the levels of chromium, nickel, titanium and copper. Each process has different levels of these additives to make versions more pliable or hardy. Most applications of an architectural nature use austenic stainless, which is not meant to be pliable. Later on I will expound upon the virtues of why these chemical additives make stainless steel so attractive for DIYers and contractors alike.

What Materials Comprise Hot-Dipped Galvanized Zinc Screws?

Two processes are at play with HDG zinc products. The first is that the composition of the interior of the screw is just plain black steel. Strong stuff, sure, but prone to corrosion by its very nature. The second process is that scientists in the 1700s came upon the idea of coating a steel object in molten zinc to increase its ability to withstand water and subsequent corrosion. Similarly, zinc had been used to plate copper to make brass during the 10th century BC. That's 12,000 years ago, and yet it was only in the last 300 years that zinc was found to be useful in coating steel and iron as well.

Which One Is Stronger?

Stainless is composed of several elements, with chromium being the highest of the additives and nickel a close second. The biggest and most important point to be had here is that the entirety of the fastener is stainless. It isn't just a coating. Its strength and rust protection are throughout. That accounts for its higher tensile strength rating. You see, companies do stress tests on fasteners to tell us what kind of insane load-bearing capacity our bolts and screws have. I'm glad they do, so I can say "tensile pound per square inch" and sound like a genius.

That being said. . .stainless steel has a tensile PSI strength of 100,000 to 150,000. It depends on composition, mostly, but its minimum acceptable PSI is 75,000. Pretty decent, if I do say so myself.

The Strength of HDG Zinc

Hot-dipped galvanized zinc metal alloy screws (boy that is a mouth full) have a tensile strength of 62,000 PSI, since they are grade 2 bolts. There are, however, more expensive versions of zinc bolts such as grade 5 and grade 8 that are common. Grade 5 has a max threshold of 120,000 while grade 8 tops out at 150,000. That sounds great, except that grade 5 and 8 are almost never galvanized. Yep, you're stuck with grade 2. Sorry, my friend.

If you're seeking a practical image of how strong these bolts can be, think about the last time you went into a Home Depot or Lowe's. It doesn't matter which, as they use the same types of racking. They're both warehouse stores, so they use beams, uprights and wood boards to display product for consumers. Every single beam that is on the front of the shelving has a zinc bolt going through the collar of the beam into the upright. That way, if there's an earthquake or you run your car into one of the shelves, it will bend, but not break. That beam bolt keeps these stores from disaster. It will do the same for your deck as well, assuming it's done correctly.

This really would be an even contest of strength if, perhaps, we were comparing stainless steel with grade 5 bolts. Oh, but we are not! Nay, we are comparing stainless with grade 2 (also known as grade A). Yes, that's right. The comparative strengths are 62,000 (average) for HDG and 75,000 (minimum) SS. That's the kind of no-brainer cage match that ends in disappointed fans!

A hot-dipped galvanized zinc steel lag screw.
A hot-dipped galvanized zinc steel lag screw.
A stainless steel lag screw.
A stainless steel lag screw.

Which One Will Look Better?

Really, that all depends, captain. Pictured above is a stainless steel lag screw below a galvanized gray lag screw. Judge for yourself. Oftentimes when contractors or DIYers build swing sets or other outdoor constructions, looks aren't what's important. It's more about function and safety. I think there's more to it. If you're building something that is going to be a reflection of your abilities, shouldn't you use the product that will give the finished product the best face possible?

In the pictures above, you'll notice the rough surface of the galvanized lag screw. If you ran your thumb along it, you would feel a scratching resistance the entire length of the screw. Not all galvanized screws are made rough or bumpy in texture. I have found some that are a bit more smooth, with a little shine to them. By and large, galvanized products are a bit ugly. Utilitarian. But do keep your eyes open for those rare shinier ones, as that can make all the difference.

Now for our other contender, let's talk about the elephant in the room. Stainless looks a bit wonky, doesn't it? Yeah it's shiny, and it's smooth, but what's with the color? It's a bit purple and a bit yellow. Yep, that's the nickel alloy showing its color. At first glance it looks a smidge like a plain zinc screw went and got sick and started turning unpleasant colors. Now look at it again. Hmm, maybe it kind of looks distinguished, doesn't it? It's not just a shiny metallic color, it's a composition of metals. Small aside: it has its own....smell too. Kind of like smelling a pocket full of loose change. Why am I going around smelling lag screws? That's a really, really good question.

In the end, it's up to your tastes. Do you prefer the more industrial feel of HDG or the refined, alien feel of stainless?

A plain zinc lag screw.
A plain zinc lag screw.

Which Will Rust First?

Please look at the plain zinc lag screw picture. It's pretty, right? Never ever use plated zinc products outdoors. While it is coated in zinc, it simply is not coated in the same method that HDG is. Don't even try it. That stuff is going to rust so quick. It's cheaper today, I know, but when your deck falls apart and you're left as a floating disembodied, you'll be regretting it.

That aside, both HDG and SS can rust. Don't believe anyone telling you they're rustproof. They're simply rust-resistant. Given the right conditions, both can be extremely vulnerable to the tragic entropy created by condensation and precipitation. A defining distinction then, is that stainless is one solid mass of metal alloys. Should someone dare to grind down a portion of the screw's exterior, they will only find more of the same on the interior. It's nickel, chromium, and the lot all-throughout.

Galvanized fasteners are essentially black steel on the inside with molten zinc on the outside. It's pretty damn difficult to burrow your way to the original steel, but it's been known to happen through wear-and-tear. When this happens, it creates an extremely weak point that can be damaged in the form of rust relatively quickly.

Stainless, on the other hand, is protected by its chromium chemical nature. Chromium uses oxygen to create a layer of rust resistance on the exterior of the screw. That leaves one glaring weakness, however. Without the oxygen needed to continue this process, this metal will rust just as quickly as the next. While there aren't too many situations without oxygen but with water present, it could happen. You don't know!

No one can tell you exactly how many years the screws you pick today will last you in the ever-present war against entropic water, but picking the hardier material may prove to be a better choice in the long run. Go for it. I believe in you.

Which Is Priced Better?

Even at this point, the two could be a toss up in your mind, but fear not, as I bring with me the decider of all. Money. Why don't we go with our familiar lag screws from earlier on. Three-eights inch diameter by four inches in length. Coarse thread, of course. One of these in HDG will run you $1.78 per lag. Stainless is a whopping $3.06. That's a huge $1.30 difference!

Price difference isn't the only thing you'll notice at the store, either. Stainless rarely comes in bulk packs for a discount. Why, you ask? Oh well...it's a huge theft risk. Those puppies are expensive, after all! While you may not care about retail politics, it does impact you a bit, as you must pay the "each" price for each of your stainless fasteners instead of the bulk price. It's an..how should I say...investment. Do not fret, mere mortal, as you can get bulk packs online oftentimes, so all hope is not lost.

For those of us that want our lag screws today, it's quite the heavy decision. Pay ~$1.50 for a galvanized lag or over $3.00 for stainless. That is a big difference, and surely one that gives galvanized zinc a leg up in our deliberations.

Which Do You Use Most?

See results

What's Better Between Galvanized and Stainless?

Let the scoring begin!

Strength: Stainless (don't kid yourself)

Looks: Tie/subjective

Rust Prevention: Stainless by more than some

Price: Galvanized by a mile

So who wins, really? I think you do, but you already knew that. Building things is expensive and stainless will set you back a few pesos, but why not do it right the first time? Why not make it an exceptional deck that you can tell all your friends is of stainless fastening. That'll be sure to get the party started.

© 2018 Alistair

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