Determining the Best Type of Fastener to Use For Outdoor Furniture Construction

If you want to learn about selecting hardware for your next outdoor furniture project, then you’ll want to read this article. Specifically, I’ll be telling you about what type of hardware will perform best, why the type of metal used for fasteners and the finish used are important considerations, and how properly protecting or limiting exposure of your furniture to wet and winter conditions can increase life span. After you’re done with this article you will understand that the best choice of hardware for your outdoor furniture project is dependent on furniture style, material used for construction, selected location for the furniture and budget.

Selecting proper hardware for your furniture will help ensure a long life span, as well as improve the overall appearance of your furniture. Part of the problem is knowing what hardware to select when there are so many options available at the hardware store. The typical Lowes or Home Depot carries a huge selection of stainless steel, hot dipped galvanized, bright galvanized, plain steel, coated steel and brass bolts, nuts, washers and screws. Each type of fastener is suitable for certain applications, but not all are ideal for outdoor furniture applications. 

In fact, choosing the wrong fasteners can greatly shorten the lifespan of your furniture, contribute to rot of wood furniture, cause unsightly staining, and even make your furniture unsafe to use. 

One thing that needs to be noted right up front is, do not ever use unprotected steel fasteners for outdoor furniture, They will rust very quickly, and the steel will react with the tannic acid in the wood causing streaks and staining. The tannic acid actually speeds up the corrosion of the fasteners. Have you ever seen a wooden fence with black streaks running down the boards from the nails? This fence was installed with the wrong type of fasteners. The same thing will happen to your furniture. Even worse, as the fasteners rust, they will speed up the decay process of the wood around the rusted fasteners, ruining your furniture and making it potentially unsafe to use.

Hot Dipped Galvanized

Screws and bolts treated by hot dipped galvanizing are specifically designed for use outdoors. Electroplated galvanized or bright galvanized fasteners ultimately will not hold up as well as the hot dipped galvanized hardware. Zinc is used as a coating in both methods, and acts as a barrier against the elements and the tannic acids in the wood. 

I strongly recommend only using screws or bolts in the construction of outdoor furniture, however. The galvanized finish on nails, either electroplated or hot dipped, can easily become damaged while hammering them in, exposing the nail head to the elements and allowing them to begin rusting quickly. 

Adequate care must be taken when installing galvanized screws. Drill pilot holes in hardwoods, and be sure to use a bit that is not worn and susceptible to skipping in the screw head. For whatever reason, the galvanized screws seem to not be as well tempered as other steel fasteners, and are more likely to either snap off or have the heads strip out while installing them. Due to the allowance required for the hot dipped coating, galvanized bolts do not have as tight of tolerance on the threads, and are more likely to strip if over tightened.

Hot dipped galvanized fasteners are a fine choice for many outdoor furniture applications, including Adirondack Chairs, but are not the best choice for use in woods, such as teak.

Stainless steel

Stainless steel is the best choice for use in woods with higher levels of tannic acid, such as teak. Stainless steel is an alloy or blend of steel, nickel and chrome. The ratio of the other metals with the steel determine the weather and corrosion resistance of stainless steel. Because the steel is mixed with other softer metals, the stainless steel is not as strong, so predrilling of screw holes is highly recommended in all applications, and essential in hardwoods such as teak and mahogany. The added corrosion resistance more than outweighs any shortcomings that the metal may have, especially in outdoor furniture applications. 

While stainless steel fasteners are the most rust resistant, they are also the most expensive of the options we are discussing. However, using stainless steel fasteners will add years of life to your furniture. In the respect, they are an investment that will pay out for years to come.

Brass

I have seen brass used in some commercially produced outdoor furniture, but do not recommend it. While brass does not form red rust, and is well suited for many wet applications such as toilets and sinks, it does tarnish and corrode. It is also very susceptible to the tannic acids in wood, which will cause it to fail more quickly. Brass screws in particular do not have sufficient strength for outdoor furniture applications.

Outdoor or deck screws

In the past several years a number of manufacturers have introduced outdoor fastening products specifically marketed for deck building. These will typically be green, gray, tan or brown. These screws are either ceramic or plastic coated to delay the metal reacting with the wood acids. The specific coating methods are proprietary to each manufacturer, and can be a combination of electroplated galvanizing and plastic, or a baked on ceramic.

I have used these fasteners in furniture applications and they perform just fine. Unfortunately, I have not come across bolts with this type of finish. The brand of screw I used was Deck Mate, and they were available in tan and brown, so that the color can be selected to better match the wood being used. These screws are ceramic coated, and the manufacturer provided a coated bit for installation, which was designed to not damage the ceramic coating at the screw head. If you choose this type of fastener, be sure to compare the cost with stainless steel, as the price will vary. If the stainless steel is reasonably comparable in cost, it would be the recommended fastener. 

Always be sure to read the manufacturers specifications on the box to be sure that the screws are suitable for your application. 

Other Considerations

If you are building furniture that will be located on a covered porch or patio where it will be protected from the elements, the concern will be the interaction between the wood and the fasteners, much more so than the weather. Furniture that will be exposed to the elements all year, such as a garden bench, or an Adirondack chair in the corner of your garden, will have to be constructed with much more care and concern to ensure that they hold up more than just one or two winters.

Additional considerations must be made beyond just the choice of what type of fastener to use, though this is very important. For example, fasteners should not be located where water where collect and sit on the fasteners for an extended period of time. The screws that attach the seat slats to an Adirondack chair are a prime example- typically these screws will be countersunk below the surface of the wood. This will allow water to collect in the screw holes, shortening the life span of all but stainless steel fasteners, and prolonging the exposure of the wood to water, which will increase the rate of decay. In applications where the furniture will be exposed to the elements year round the screw heads should be driven flush with the surface of the surrounding wood. 

Construction and design of the furniture are also important considerations. Are the horizontal surfaces of the furniture constructed in such a way that will allow them to shed water, rather than collect it? Think of a picnic table with a slatted or board top. The gaps between the boards allow water a way to run off the top and not pool up. 

Conclusion

Stainless steel is usually the best choice for outdoor furniture applications, though the cost may be prohibitive for some. There are other less expensive fastener options available that will perform acceptably. Do not use unprotected steel fasteners for outdoor furniture applications under any circumstances. Know where and how you intend to use your furniture and design it for the conditions it will be subjected to.