Outdoor wooden furniture and structures like decks, pergolas, and fences can provide great aesthetic value and functionality to your yard. However, untreated wood that is constantly exposed to the elements will deteriorate fairly quickly. Treating logs and lumber intended for outdoor use is important for protecting the material and extending its lifespan. With the proper treatment and care, you can help your outdoor wood projects hold up for many years to come.
Selecting the Right Wood
When choosing wood for an outdoor project, opt for species that are naturally resistant to rot and insect damage. Some of the best woods for outdoor durability include:
- Cedar – Has natural oils that act as preservatives. Good resistance to weathering and decay.
- Redwood – Dense grain makes it resistant to insects and moisture. Ages gracefully.
- Teak – Contains oils that help it stand up to weathering. Ages to a silver-gray color.
- Ipe – Extremely dense and durable tropical hardwood. Resistant to rot and insects.
- Pressure-treated pine – Pine infused with preservatives under pressure. Budget-friendly treated option.
Stay away from woods like pine, fir, and spruce which have low natural rot resistance. Even with treatment, these woods will deteriorate more quickly than durable species when used outdoors.
Opt for wood graded for outdoor use whenever possible. Look for terms like “decking” or “construction heart” which indicate superior durability and structural integrity.
Choose wood boards with a kiln-dried (KD) stamp. Kiln drying reduces moisture content which helps prevent cupping and decay.
Inspect wood carefully for checks, knots, and splits which can allow moisture inside and lead to rot. Avoid wood with an excessive amount of defects.
Using Preservatives and Water Repellents
Preservative Treatment Options
- Pressure treating – Forced infusion of chemicals like copper azole under high pressure. Available for common woods like pine.
- Brushing/spraying – Applying preservative liquids to wood’s surface. Less effective than pressure treating.
- Dipping – Submerging end grains in preservative coating to protect vulnerable cut ends.
- Borate treatment – Borate powder or solution applied to wood to deter insects and fungi.
- Heat treatment – Exposing wood to high heat eliminates moisture and makes it less appetizing to wood-destroying organisms.
Water Repellent Options
- Paint – Opaque solid colored paint adds moisture protection. Needs regular recoating.
- Stain – Pigmented stain tints wood and seals surface. Translucent to show some grain.
- Clear sealer – Protects surface without changing natural color. Needs frequent reapplication.
- Oils – Oils like tung and linseed soak into wood and reduce moisture absorption.
- Waxes – Form protective coating and need reapplication every 1-2 years.
- Polyurethane – Clear varnish-like coating repels water. Needs refinishing periodically.
Treating Logs
1. Start with Quality Logs
Seek out logs with thicker sapwood, which is more rot-resistant than the inner heartwood. For stackable outdoor furniture like chairs, look for straight logs with even diameter. Curved logs can be used decoratively.
Use logs with intact bark and avoid excessive cracking which allows moisture inside. Filling cracks with a flexible caulk immediately helps limit water intrusion.
Cedar, cypress, oak, and locust are naturally durable log options. Pine logs will need extensive preservative treatment for outdoor use.
2. Remove Bark (Optional)
Removing outer bark exposes the rot-resistant inner heartwood and allows preservatives to penetrate. This can give logs a nice rustic look over time.
Use a drawknife, chisel, or power washer to remove loose bark. Taking off too much bark can dry logs out excessively though. Leaving some bark intact helps regulate moisture.
3. Apply Preservative
Applying a preservative treatment helps protect logs from rot, fungi, and wood-boring insects. Some options:
Brush on preservative oil– Apply liberally to bare logs. Let soak in. Recommended to treat cut log ends.
Borate powder – Sprinkle borate powder on log surface. Scrub in with a stiff brush to work into cracks.
Wood preservative – Brush on liquid wood preservative designed for outdoor use per manufacturer instructions.
Water repellent – Coat logs with a breathable water repellent sealant to fortify against moisture damage.
Reapply preservatives annually or as directed. Treated logs may still crack over time. Fill new cracks with a flexible sealant.
4. Add Finish (Optional)
For added protection and aesthetics, consider applying an outdoor wood finish:
- Stain – Penetrating oil-based stain adds rich color while protecting from UV rays.
- Paint – Exterior grade opaque paint provides a strong moisture barrier.
- Clear sealer – Clear water-repellent sealant preserves natural look of wood while protecting surface.
Use finishes specially formulated for outdoor wood. Follow all label directions closely. Expect to refinish periodically as the coating wears.
Pro tip: Always finish all sides of logs for balanced moisture protection.
Treating Dimensional Lumber
Dimensional lumber is boards and timbers sawn from larger logs for use in wood projects. Follow these tips to effectively treat dimensional lumber for outdoor durability:
1. Choose Pre-Treated Lumber
Look for pressure-treated (PT) lumber at lumberyards and home centers. This process forces preservative chemicals deep into the wood for long-lasting protection.
Common preserved lumber options:
- ACQ – Alkaline copper quaternary compound treatment. Greenish tint.
- Copper azole – Copper combined with organic azole fungicide. Golden/brownish color.
- Ammoniacal copper zinc arsenate (ACZA) – Contains copper, arsenic, and zinc.
Pre-treated lumber stamped for ground contact can be buried in soil. Above ground applications only require less intensive preservative levels.
2. Apply Additional Preservative
Even pressure-treated lumber can benefit from supplemental brush-on preservative treatment:
- End grain – Brush preservative liberally on fresh cut ends which act like straws absorbing moisture into the wood’s interior.
- Drill holes – For large timbers, drill holes and fill with preservative to saturate interior areas. Plug holes afterwards.
- Penetrate cracks – Flow preservative into any cracks with an eyedropper and let soak in fully. Then seal crack with caulk.
- Bolt holes – Dab preservative on holes drilled for hardware to prevent water intrusion.
- Reapply annually – Brush preservative over visible surfaces each year as routine maintenance.
3. Add a Protective Finish
While optional, additional coating with a water-repellent wood finish will provide enhanced surface protection:
- Use an exterior grade penetrating oil or stain that contains mildewcides and UV blockers.
- Clear water sealants also soak in to fortify wood against moisture damage.
- Paint or opaque stains provide extra weather and UV rays protection.
- Reapply finishes periodically as they erode to maintain protection.
4. Allow Wood to Adjust to Moisture
Once installed, let wood acclimatize for several sunny days before applying any protective finish. This allows wood to equalize moisture content and dry from any treatment chemical surplus. Starting with properly dried wood helps maximize coating adhesion and performance.
Maintaining Outdoor Wood
Proper maintenance is key to getting the longest service life from outdoor wood projects. Follow these maintenance tips:
- Inspect wood yearly for signs of wear, cracking, insect damage, or fungal growth. Address issues right away before they worsen.
- Re-apply protective finishes like stains or water sealants as needed to refresh weathered surfaces.
- Remove splintering or cracked wood planks that could allow moisture intrusion.
- Ensure proper drainage so water flows away from wood structures. Prevent puddling.
- Keep soil or mulch at least 6 inches from siding, posts, and beams to discourage termite and carpenter ant access.
- Clean outdoor wood periodically with a brush and mild cleaner. Avoid pressure washing which can damage surfaces.
- Consider re-treating inland wood projects every 2-3 years for optimal protection
Proper preservative treatment paired with vigilant maintenance helps ensure your outdoor wood projects withstand the elements so you can enjoy them for years to come.
Frequently Asked Questions
What is the most durable wood for outdoors?
Teak, cedar, and redwood are naturally durable woods that hold up very well outdoors. Ipe and black locust are also extremely rot-resistant choices. Pine is inexpensive but will deteriorate quickly without extensive treatment.
How long does treated wood last outside?
Treated lumber that is properly maintained can last 15-30 years outdoors since the preservatives protect it from moisture, fungi and insect damage. Regular inspection, cleaning and refinishing extends service life.
Should pressure treated wood be sealed?
It is recommended to add a protective finish like penetrating stain or sealer to pressure-treated lumber for enhanced weather-resistance. The finish soaks in to fortify the interior preservatives. Reapply the finish periodically as it wears away.
What is the most weather resistant outdoor wood stain?
Oil-based penetrating stains that contain UV blockers, mildewcides and water repellents provide the most durable and weather-resistant finish. Semi-transparent stains allow some of the wood’s natural color to show. Opaque stains provide maximum UV protection.
Do logs need treatment for outdoor use?
Untreated logs will eventually crack, rot, and invite insect damage when left outdoors. Applying preservative oils, sealants or finishes is highly recommended to protect logs used for furniture, retaining walls and other outdoor structures. Annual reapplication helps maintain protection.
How long does Thompson’s Water Seal last on wood?
On decking and exterior wood, Thompson’s Water Seal can last 1-3 years depending on the exposure and traffic. More frequent re-coating is needed on wood flooring or furniture that sees heavier use. Thompson’s recommends re-applying annually for best protection.
What is the most waterproof sealant for wood?
Of available clear wood sealants, varnish or polyurethane will provide the most waterproof and durable finish. Multiple coats are needed for a strong moisture barrier. These sealants require periodic sanding and reapplication as they wear over the years with outdoor exposure.
Can you use Thompson’s Water Seal on pressure treated wood?
Yes, Thompson’s Water Seal or other water-repellent finishes can be applied to pressure treated wood for added weather-resistance. Allow the wood to dry fully before applying the sealant so it penetrates deeply. Thompson’s recommends 2 coats on PT wood for maximum protection.
How do you weatherproof plywood outside?
To weatherproof plywood for exterior use, opt for marine grade plywood which is designed to resist moisture. Apply a primer, then coat with a high-quality exterior grade latex paint. For best results, add a final coat of spar urethane varnish to make the surface totally waterproof.
What kind of paint should be used on exterior wood?
Exterior grade acrylic latex paints provide good coverage and protection on outdoor wood surfaces like siding, trim, fences and furniture. Oil-based alkyd paints are also highly durable options. Paint formulated specifically for decks, patio furniture or siding offers enhanced durability.
Conclusion
Ensuring lumber and logs are properly treated and maintained for outdoor exposure is crucial to get the most life from beloved wood projects. Take time to carefully select suitable wood species, apply preservative treatments, and finish with a protective sealer, stain or paint. Keep wood well-maintained and catch issues early before they escalate. Your diligence will be rewarded with many years of enjoyment of handsome, durable outdoor wood structures and furnishings. With the right preparation and care, your wood projects can gracefully withstand all of nature’s challenges.