Select the right kind of finish to get the best results on your outdoor projects.
When you build an outdoor wood project, you want it to look great and last. The best way to get both is to apply a good exterior finish. Finding the right one can be more challenging than finding an interior finish, because an exterior finish has to do more things.
An interior finish needs to make the wood look good and maybe protect against scuffs and abrasions, along with the occasional spill. An exterior finish needs to protect against more scuffs and abrasions, to keep out moisture from the air and from precipitation, to prevent damage from ultraviolet (UV) rays, to withstand extremes of cold and heat, and, of course, make the wood look good.
Thankfully, there are multiple types of finishes that can do the job, and you can find them all in home centers. Here’s the information you’ll want to know about several popular types.
1. Exterior Wood Sealer
If you want a finish that’s easy to apply and that won’t change the color of the wood, exterior wood sealer is a good choice. It can be wiped, rolled, sprayed, or brushed on, so you can apply it without having to worry about any special skills or techniques. That makes it safe if you’re not experienced with finishing.
A big part of why sealer is easy is that it stays clear. Sealer will highlight the grain—along with any other marks or imperfections in the wood—but it doesn’t change the wood’s color. That’s great if you want to show off the wood, but it may not be as good if the wood color is unattractive, like really green treated lumber, if the color is inconsistent, or if you’re refinishing old, discolored wood.
Wood Sealer can also be used like a primer if you plan to paint. Just be sure to wait the recommended amount of time after you seal the wood before you paint.
2. Exterior Oil Finish
Exterior oil finishes act a lot like interior oil finishes you might have tried, such as tung oil or linseed oil. In fact, many exterior oil finishes contain the same base oils. Additives such as synthetic resins (alkyds) and UV inhibitors often get added to increase durability for outdoor use.
Exterior oil finishes penetrate into the wood, and may take a couple coats to fully cover, especially on very dry woods. They generally add a nice amber tone to the wood while retaining the natural feel. Oils may have to be renewed more often—every year or two—because they wear away more quickly than film-building finishes like wood sealer (above) or spar varnish (discussed later).
Exterior finishes offer beauty that (only sort of) lasts
When you finish an indoor project, it’s pretty much forever. Outdoor finishes just don’t last as long. Exposure to the elements, especially sun and rain, break down even the best exterior finishes. The more protected the piece is, the longer the finish will last, so a project on a covered patio may look great much longer than one that sits out fully exposed in the yard. Be prepared to at least touch up if not completely refinish exterior wood projects every two to three years.
3. Spar Varnish/Spar Urethane
Spar varnish has been around in one form or another since the days of sailing ships. Most of the time these days you’ll find spar urethane, which simply means it’s made with synthetic resins, rather than the natural resins that were originally used.
Either way, spar varnish creates a very strong exterior finish that builds a thicker film with every coat you apply. If you want a “furniture” look on your outdoor project, spar varnish is worth a try. The color is clear to light amber, and you can usually find satin or gloss sheens.
Spar varnish is more challenging to apply than some exterior finishes. It will require several coats, and the thickness means you have to apply it carefully, as you would with an interior varnish, to avoid brush marks. But the results can be worth the extra effort for outdoor furniture.
As spar varnish wears, it can chip and flake, which may require sanding before you can reapply more varnish.
4. Exterior Wood Stain (Deck Stain)
Home centers have a big selection of exterior wood stains. They’re usually referred to as deck stains, but they work great for staining all kinds of outdoor projects. Usually, you’ll find several premixed wood-tone colors, such as “natural cedar” on the shelf, along with displays showing other deeper wood tones you can have custom mixed, just like paint.
You’ll even find bold colors like blues, reds, and greens that might not be great for a deck but can be dynamite for a piece of outdoor furniture, a shed, or other smaller projects. Just remember stains penetrate into the wood so, once you’ve committed to a dark or bold color, it can be tough to go back—at least without a lot of stripping and sanding.
When you shop for outdoor stains, you’ll find them in different levels of transparency, which determines how much of the wood will show. You can learn more about what that means in this video.
Dry and clean are key to success
With any finishing job, the prep work is a big key to success. To make an exterior finish last, prep work can be even more important.
First, make sure the wood is dry. If you’re building something new, that’s probably not an issue, unless you are using treated lumber. It can be very wet and may need one to six months to dry out enough for finish. Learn more about staining treated lumber here.
Second, make sure the wood is clean, meaning free of dirt or mildew, and from sawdust or other contaminants that can prevent the finish from really sticking to the wood.
Just because you’re building with wood, that doesn’t mean you have to, or maybe even want to, have the wood grain show. That’s why exterior paint is still a very viable option for your outdoor projects. Exterior paint is durable, it’s available in essentially any color you could ever imagine, and it’s available everywhere.
Paint is also easy to apply with a brush or a roller. Check out this video to learn more about how to pick the right roller for painting furniture. And many of today’s paints are made as “paint plus primer,” which means you don’t have to go through an extra step—though you may still want two coats to ensure maximum durability outdoors.
You can see that, when it comes to finish for exterior projects, there are a lot of great options. Choose the one that gives the look you want and the protection you need, and then maintain the finish as necessary to enjoy your outdoor projects for a long time.