Using untreated wood outdoors exposes it to the elements – rain, sun, snow, and fluctuating temperatures. This can lead to cracking, warping, rotting, and decay. Treating wood properly helps protect it from the environment so your wood projects last longer outdoors. There are several effective options for treating and sealing untreated wood before using it for decking, fencing, pergolas, planter boxes, and other outdoor structures.

Should You Use Treated or Untreated Wood Outdoors?

When using wood outdoors, you have two main options:

Treated Wood

• Treated lumber has been impregnated with chemical preservatives to help resist rot, fungal decay, and insect damage. Common treatments include:
• CCA (chromated copper arsenate) – a pesticide preservative once widely used on decks and playsets but phased out for residential use since 2004.
• ACQ (alkaline copper quaternary) – contains copper and quaternary ammonium, active against fungal decay and insects.
• Copper azole – uses copper as the main fungicide and insecticide.
• Treated wood is readily available at most lumberyards and home improvement stores. It costs more than untreated wood but can last over 25 years outdoors.
• Use treated wood for any direct ground contact like fence posts and deck supports. The preservatives help resist constant moisture exposure from the soil.

Untreated Wood

• Untreated wood is cheaper than treated lumber and contains no chemical preservatives. Types like cedar, redwood, cypress have natural decay resistance.
• Use untreated wood for above-ground projects like raised garden beds, benches, pergolas, picnic tables, plant boxes, and deck boards.
• You must properly seal and maintain untreated wood to help it withstand outdoor elements.

So in summary, use treated wood for ground contact and untreated wood for everything else outdoors. But be sure to adequately protect and seal the untreated wood against weathering.

How to Prepare Untreated Wood for Outdoor Use

Follow these steps to get untreated wood ready for exterior projects:

1. Select the Right Wood

Choose untreated wood that withstands weather well:

• Cedar – Exceptional rot and insect resistance. Popular for decks, shingles, fences. Red cedar has better durability than white.
• Redwood – Naturally decay-resistant softwood. Used for decks, siding, outdoor furniture. Has good dimensional stability.
• Cypress – Resilient against rot and insects. Good for decking, shutters, framing. Has an attractive grain pattern.
• Teak – Excellent weather resistance. Used for boatbuilding, outdoor furniture, decking. Needs no protective finish.
• Ipe – Extremely dense South American hardwood. Expensive but very durable and low maintenance.
• Mahogany/Sapele – Tropical hardwoods used for decking, siding, outdoor furniture when properly finished.

Other durable options: Black locust, jarrah, white oak

Decay-prone woods like fir, pine, spruce require extra protection. Avoid particleboard, plywood, MDF.

2. Check Moisture Content

• Wood needs to be dried to 15% moisture content or less before finishing and installing outdoors.
• Use a moisture meter to test. Higher moisture causes wood to shrink, split, twist, or crack when exposed to sun.
• Allow fresh cut wood to air dry 6-12 months. Kiln drying accelerates drying.

3. Remove Surfaces Defects

• Inspect wood for knots, splinters, cracks, holes. Sand smooth any rough areas.
• Use wood filler or epoxy to patch small holes and defects. Helps achieve an even finish.

4. Sand the Surface

• Sand wood thoroughly with 120-150 grit sandpaper to remove mill glaze and open the grain.
• Always sand in direction of the wood grain. Go up to 220 grit for extra smoothness.
• Sanding improves adhesion of stains, paints, and film-forming finishes.
• Remove all sanding dust with a vacuum, tack cloth, or dry rag.

Proper prep is vital for exterior wood to look great and last. Take time to choose durable wood, let it dry adequately, remove defects, and sand for the ideal surface to finish.

What is the Best Exterior Finish for Untreated Wood?

You need to apply some type of protective finish to untreated wood used outdoors. Consider these excellent options:

Film-Forming Finishes

• Spar urethane – Forms a glossy coating that repels water. Flexible finish good for doors, outdoor furniture. Requires sanding between coats.
• Exterior latex or oil paint – Provides a decorative, water-resistant coating that needs periodic repainting. Good mildew resistance.
• Oil-based varnish – Forms a durable, glossy film finish ideal for items exposed to weathering. Use marine-grade for boatbuilding.
• Epoxy resin – Used to completely seal and coat surfaces for a glass-like finish. Good for bars and tabletops.

Penetrating Wood Sealers

• Tung oil – Provides a resilient, water-repellent finish that protects well against moisture. Enhances natural wood grain.
• Linseed oil – Penetrates deep into wood for good weather resistance. Has to be reapplied annually.
• Penofin oil – Contains UV blockers. Flexible finish needs reapplication every 1-2 years.
• Bleaching oil – Contains pigments to add color as it seals and weathers wood naturally. Low maintenance.
• Teak oil – Penetrates to protect woods like teak, ipe, and mahogany. Contains UV inhibitors.

Water-Repellent Wood Sealers

• Timber oil – Low-build penetrating finish protects against moisture, mildew, UV rays. Won’t crack, peel.
• Silicone water sealers – Repels water to prevent warping, splitting. Doesn’t protect against UV damage.
• Beeswax wood conditioner – Contains natural waxes, oils, tree resins. Enhances natural color as it seals surface.
• Mineral oil – Penetrates deeply to protect wood from within. Needs frequent reapplication. Food safe option.

Stained Wood Sealers

• Semi-transparent deck stain – Penetrating oil-based formula enhances wood grain and color while protecting exterior wood.
• Solid color deck stain – Opaque, pigmented stain masks wood grain but shields better from UV rays. Film-forming.
• Wood preservative stain – Contains fungicides, insecticide to deter pests, mildew, decay. Doesn’t last as long as paint or varnish.

Consider project use, desired look, and maintenance level when selecting the best sealant. Film-forming finishes offer the most protection but need more prep and maintenance. Penetrating oils are lower maintenance but require more frequent reapplication.

Steps to Finish and Seal Untreated Wood

Follow these key steps to properly treat and seal untreated exterior lumber:

1. Prep the Wood Surface

• Ensure wood is cleaned, dry, and sanded up to 220 grit.
• Vacuum away all dust. Wipe with a tack cloth.
• Make sure moisture content is below 15%.

2. Apply Wood Conditioner

• For soft or porous woods, use a wood conditioner before staining.
• It penetrates deep to even out finish absorption for a more uniform look.

3. Apply Your Selected Finish

• Carefully read and follow all product label directions.
• Use a high-quality natural bristle or foam brush. Avoid over-brushing.
• Maintain a wet edge to prevent lap marks with uniform brush strokes.
• Thin coats are better than thick coats that may sag or drip.

4. Allow Proper Drying Time

• Let stains dry 24-48 hours and finishes dry 1-2 weeks before use.
• Check product labels for specific dry times based on humidity and temperature.
• Cold, humid weather increases dry times.

5. Apply Additional Coats

• For maximum protection, apply 2-3 thin coats of exterior finishes like paint, varnish, or urethane.
• Lightly sand with 220 grit sandpaper between coats to improve adhesion.
• Add another coat every 2-4 years for maintenance.

6. Check for Even Coverage

• Ensure you have an even, smooth coating across the entire wood surface.
• Look for any drips, runs, or thin spots and apply additional finish coats to build up those areas.

With proper prep, application, and drying time, these steps will provide a long-lasting, protective finish to keep your outdoor wood looking its best. Maintain the finish with periodic cleaning, light sanding, and reapplication as needed.

5 Outdoor Projects for Treated Wood

Here are 5 great ways to utilize untreated wood outdoors with the proper protective treatment:

1. Backyard Pergola

• Build a pergola over a patio or deck to provide cool shade using cedar beams and rafters.
• Use exterior paint or semi-transparent stain to finish the wood.
• Add weather-resistant fabric shade sails on top for adjustable sun coverage.

2. Modern Planter Boxes

• Construct contemporary planter boxes with smooth planks of redwood or cypress.
• Use Penofin penetrating oil or spar urethane to seal the untreated planter wood.
• Display them on a patio or against the house to grow flowers, vines, or vegetables.

3. Rustic Wood Sign

• Make a custom address or family name sign from unfinished cypress, cedar, or redwood boards.
• Paint or stain the sign with exterior products and seal with a protective polyurethane finish.
• Hang above the front door or suspend from the front porch.

4. Backyard Wood Fence

• Install wooden fence panels stained a semi-transparent medium brown for outdoor privacy and wind protection.
• Use naturally rot-resistant cedar or redwood boards so the panels require minimal maintenance.
• Add decorative post caps on top of 4×4 posts for an upgraded look.

5. Curved Garden Bench

• Build a gracefully curved outdoor bench using durable, easy-to-shape cedar.
• Sand and finish the bench and supports with marine spar varnish for protection from sun and rain.
• Place in a garden bed, under a tree, or by a pond to enjoy the outdoors.

Let your imagination run wild to create your own functional, beautiful wood projects to enhance your outdoor living space. Just be sure to properly prep and finish the untreated wood first!

Frequently Asked Questions About Treating Outdoor Wood

Many common questions come up regarding the best ways to treat and finish exterior wood projects:

Should I use treated or untreated wood for outdoor projects?

Use treated wood for any contact with the ground – posts, supports, fence slats. Use untreated wood for above ground projects like raised beds, benches, pergolas. Make sure to adequately finish and maintain the untreated wood.

How long does untreated wood last outside without treatment?

Most untreated woods like pine or fir will start to weather, decay, crack and split within just a few months outdoors if left unfinished. More naturally rot-resistant woods like cedar, redwood, or teak can last 1-2 years with no treatment in mild climates before signs of deterioration.

What’s the most waterproof sealant for outdoor wood?

Spar varnish and epoxy resin provide the most waterproof, protective seal for exterior woods. Oil-based paints and penetrating oils like Penofin are also excellent water-repellent finishes. Avoid latex paints alone.

Should I seal all sides of outdoor wood?

Yes, it’s important to thoroughly seal all sides – front, back, edges, and ends – on any outdoor wood using the finish of your choice. Otherwise moisture can penetrate untreated wood surfaces accelerating decay.

How often should you re-seal outdoor wood?

Many film finishes like varnish, paints, stains last 2-4 years before needing reapplication. Penetrating oils may need reapplying every 1-2 years. Inspect annually and reapply when finish appears worn, dull or compromised.

What kind of wood is best for outdoor furniture?

Teak is the gold standard for outdoor furniture but very expensive. More budget-friendly options that still resist weathering include cedar, redwood, cypress, treated pine, eucalyptus, and acacia. Use an exterior wood finish to help protect the furniture.

Can unfinished wood be used for raised garden beds?

Yes, versatile untreated cedar and redwood are great choices for raised beds. Just be sure to line the inside of the beds with a non-toxic pond liner or plastic sheeting first before filling with soil to prevent premature wood rot.

How do I get a smooth finish on exterior wood?

Getting a blemish-free, smooth wood surface takes diligent prep – sanding up to 220 grit, cleaning away all dust, applying conditioner, using high-quality primer, and applying multiple thin finish coats. Allow proper dry time between coats.

Conclusion

The key to using untreated wood outdoors is properly preparing the surface and sealing it with a protective finish. Assess your project plans and service conditions. Select appropriately resilient wood species. Allow adequate drying time. Sand, clean, and apply your preferred exterior wood sealant. Aim for 2-3 thin, even coats. With appropriate treatment you can have beautiful, long-lasting outdoor wood projects. Just be sure to mind the details in wood selection, prep, application, and maintenance. Your properly finished untreated wood will give you enjoyment for years to come.

How To Treat Untreated Wood For Outdoor Use

Using untreated wood outdoors exposes it to moisture, sunlight, pests and other elements that can quickly lead to decay, mold, warping and structural damage. While treated lumber contains preservatives to resist rot and insect damage, untreated wood requires special preparation and protection to withstand the outdoor environment.

This guide covers how to properly treat and protect untreated wood to extend its life and performance for decking, fencing, pergolas, raised beds, outdoor furniture and various exterior projects.

Select Appropriate Wood Species

Choosing naturally durable wood species is the first step for outdoor projects using untreated lumber. Look for woods with natural resistance to moisture, fungi and pests. Top options include:

• Cedar – Excellent rot resistance. Popular for decks, shingles, outdoor furniture. Red cedar is more durable than white.
• Redwood – Decay-resistant softwood perfect for decks, fencing, landscaping. Stable wood that handles weather well.
• Teak – Tropical hardwood with exceptional resistance to moisture, bugs, weathering. No finish needed.
• Ipe – Extremely dense Brazilian walnut. Resilient outdoor wood but expensive. Needs no treatment.
• Cypress – Rot-repellent wood ideal for outdoor furniture, decking, landscaping. Has attractive grain patterns.

Other naturally durable woods are black locust, jarrah, osage orange, sassafras, mesquite, and white oak. Avoid pore-prone woods like pine, fir and spruce unless properly treated. Also avoid manmade boards like particleboard and MDF.

Allow Wood to Dry Thoroughly Before Finishing

Freshly milled lumber needs time to dry out and adjust moisture content for ideal finishing:

• Allow wood to air dry 6-12 months until moisture content reaches 15% or less.
• Use a moisture meter to test moisture levels in wood.
• Kiln drying accelerates drying times for milled lumber.

Applying finishes too early causes unsightly cracks, splits, warps and stains when wood shrinks outdoors.

Prep the Surface for Finishing

Proper surface prep contributes to a long-lasting, uniform finish:

• Sand wood with 120-150 grit paper to remove mill glaze and open the grain. Always sand in the direction of the grain.
• Progress through finer grits up to 220 for final smoothing.
• Vacuum away all dust, then wipe clean with a dry tack cloth.
• Fill any small defects with wood filler and allow to dry completely.
• Ensure the surface is clean and dry before applying any finish.

These steps help finishes fully penetrate and bond well to the wood surface.

Choose an Effective Exterior Wood Finish

You must apply some type of protective finish to untreated wood used outdoors. Consider these top options:

Penetrating Oils

• Tung oil – Provides a flexible, water-resistant finish. Enhances natural wood grain well.
• Teak oil – Contains UV blockers to protect against sun damage. Repels moisture and mildew.
• Linseed oil – Must be applied annually but penetrates deep to protect wood.
• Mineral oil – Cheap, food-safe option that resists water and weathering. Requires frequent reapplication.

Film-Forming Finishes

• Marine spar varnish – Forms a glossy, durable coating to resist moisture. Flexible finish good for outdoor furniture.
• Exterior latex or oil paint – Pigmented opaque finish needs repainting every 4-8 years. Resists mildew growth.
• Epoxy – Coats surfaces with a thick, glass-like finish for bar tops, tabletops.
• Spar urethane – Applies a protective topcoat that seals out water. Use for doors, window boxes, railings.
• Oil-based polyurethane – Forms a durable, abrasion-resistant film finish. Use on outdoor fixtures, benches, planters.

Water-Repellent Wood Sealers