Selecting a durable, weather-resistant finish is crucial for any deck, fence, bench, planter box, or exterior door that endures long-term exposure. This woodworking finishing for outdoor projects guide covers the key factors in picking an optimal outdoor finish to withstand the elements while enhancing and safeguarding your woodworking creations.
Wood projects destined for the outdoors require special consideration when it comes to choosing a protective finish. Unlike indoor furnishings, outdoor woodworks face the unrelenting bombardment of sun, rain, snow, and temperature swings. Using the wrong type of finish can lead to cracks, peeling, mold growth, and premature rotting of the wood.
| Key Takeaways |
| Spar varnish and teak oil provide optimal UV and water protection for outdoor wood. |
| Properly prepare surfaces by sanding, conditioning, and filling cracks before finishing. |
| Apply at least 3-4 thin, even coats of exterior varnish for sufficient protection. |
| Allow adequate drying time between finish coats. |
| Expect to refresh the finish every 2-5 years depending on quality and exposure. |
| Watch for fading, mildew, flaking as signs it’s time to renew the finish. |
| Clean surface and scuff sand before reapplying varnish or teak oil. |
| Maintaining the finish properly keeps outdoor woodworking projects looking their best. |
Evaluating Outdoor Finish Options
While stains, paints, oils, and varnishes might seem interchangeable, important performance differences make certain finish types better choices over others for exterior applications.
Stains allow the wood grain to show through while adding a hint of color. Common varieties like acrylic latex and oil-based penetrate and protect the surface. Though affordable and easier to apply than film-building finishes, most stains lack adequate protection on their own against moisture damage. They work best as a preparatory base layer.
Paints excel at fully obscuring the underlying wood texture with opaque, vibrant hues. Alkyd and acrylic latex formulas resist fading, chalking, and blistering when exposed to sun and water. But the thick coating can crack over time as wood expands and contracts, allowing moisture to seep in.
More durable exterior options are penetrating oils and varnishes that soak into and seal off the wood pores. These withstand UV rays while allowing the natural movement of the wood without deteriorating. We’ll explore these promising picks next.
Preparing Raw Wood for Finishing
Since all finishes adhere best to clean, absorbent surfaces, take time to prep and condition new wood intended for the outdoors.
Begin by using 120-150 grit sandpaper to lightly abrade and smooth any rough sawn wood. This removes mill glaze and opens the grain to accept the finish. Carefully dust off sanding residue with a brush or vacuum.
Next, an application of wood conditioner helps regulate moisture absorption, preventing the finish from raising the wood grain. Allow this to fully dry.
Fill any knots, cracks or nail holes with compatible wood filler designed for exterior use. Once cured, sand smooth and level with the surrounding surface.
Finally, let the bare wood acclimate to the ambient outdoor temperature and humidity for 2-3 days before finishing to prevent expansion/contraction issues down the road. Now it’s ready for a protective topcoat.
Brush On Multiple Coats of Exterior Varnish
When applying finishes outdoors, natural bristle brushes generally produce a smoother, more consistent flow versus roller or spray methods. Work in the shade and avoid finishing on excessively hot, humid or damp days.
Spar varnish (or marine varnish) makes the optimal protective topcoat for outdoor wood. Formulated to resist sunlight, water, and chemicals, it provides a crystal clear, vibrant finish that lasts up to 7-10 times longer than interior varnishes before needing maintenance.
Apply a minimum of 3-4 thin, even coats following the manufacturer’s instructed recoat times to build adequate protection. Lightly sand with 220 grit paper to smooth out brush marks and ensure adhesion between coats. Adequate film thickness and proper curing delivers durability measured in years rather than months.
Teak oil is another excellent penetrating finish option for outdoor projects. Containing UV inhibitors, it accentuates the natural color tones of wood species like cedar, redwood, pine, oak and mahogany while safeguarding against moisture, mildew, and sun damage. Wipe-on application makes it easy for quick renewal coats in the years ahead.
Maintaining the Outdoor Finish Over Time
With exterior wood projects, expect to clean and reapply protective finish coats every 1-2 years to keep wood looking its best. However, a quality spar varnish or teak oil finish may last 3-5 years or longer before needing attention.
Watch for telltale signs like fading, mildew growth, flaking or alligatoring that signal time for maintenance. Gently scrub away these flaws along with dirt and environmental contaminants using a soft nylon brush, wood cleaner, and rinse water.
Once the surface dries thoroughly, evaluate if the existing finish has worn too thin in areas to protect the underlying wood. Scuff sand if necessary to improve adhesion before brushing on 1-2 renewal coats of varnish or teak oil. This refreshes the finish while further extending the life of your woodwork investment.
Key Takeaways
- Spar varnish and teak oil finishes provide optimal UV and water protection for outdoor wood.
- Proper surface preparation improves finish adhesion and durability.
- Apply multiple thin coats for sufficient protection, allowing adequate drying time between coats.
- Expect to refresh the finish every 2-5 years depending on quality and exposure levels.
Maintaining a resilient outdoor wood finish requires diligence and reapplication over time. But the effort delivers lasting protection and beauty for your woodworking creations. Share your own outdoor finishing tips and lessons learned in the comments below!
Frequently Asked Questions
What are some DIY ways to weatherproof plywood for outdoor use?
You can help protect exterior grade plywood for projects like planter boxes by sealing all edges with quality exterior caulk. Use an oil-based primer followed by 2-3 coats of exterior latex paint for additional water resistance. Consider adding metal flashing or aluminum angles along the bottom edges to prevent wicking up of ground moisture.
Can I use the same finish on outdoor furniture that I would on a deck or pergola?
Generally lighter applications of exterior oil finishes work well on outdoor furniture, allowing the wood grain to show through. Meanwhile, opaque stains or paint finishes make better sense for decks, fences, pergolas and other solid structures to fully protect the wood from UV damage.
What type of wood holds up best outside without a protective finish?
Heartwood from durable species containing natural oils like teak, ipe, cedar, redwood, and white oak resist rot, insects, and moisture damage for many years without a protective topcoat. However, all woods will eventually grey and crack from sun exposure if left unfinished.
Is there a simple way to renew the finish on my faded deck without having to strip and refinish the whole thing?
A good option is using a revitalizing deck coating designed for renewing old finishes and sun-faded decks without the need for sanding or stripping. After cleaning the surface, apply by sprayer or roller over the existing finish to restore color and protection.
Can I apply polyurethane over an oil-based stain to add extra protection outside?
Yes, once an oil stain has fully cured, applying 1-2 coats of a spar polyurethane (designed for exterior use) adds extra defense against moisture, UV damage and dirt accumulation. Be sure to stick with the same brand of products for compatibility.
How do I get rid of mold growth on an outdoor wood finish?
Mix up a solution of 1 part bleach and 3 parts water and use a soft nylon scrub brush to gently clean away the mold. Allow the wood to dry 2 sunny days. Then apply a quality exterior wood cleaner followed by a fungicide solution like Concrobium to help prevent future mold growth. Once dry, reapply your protective outdoor finish.
When refinishing a previously varnished deck, is it necessary to strip off all old finish first?
In most cases, you can prep the surface by cleaning with a wood restorer solution and scuff sanding to de-gloss before applying new coats of varnish. Remove any failing finish in bare spot areas first. Completely stripping back to bare wood becomes necessary if there are extensive signs of peeling, flaking or alligatored finish.
Additional Resources
For more tips on successfully finishing woodworking projects intended for outdoor use, check out these helpful references:
Applying Spar Urethane from Woodcraft
Exterior Wood Finishes at Family Handyman
DIY Network’s Guide to Outdoor Wood Finishing
How to Finish Outdoor Wood, Youtube.com
Best Outdoor Wood Sealers, BobVila.com
Exterior Wood Finishing Tips, PopularWoodworking.com