Bamboo is a versatile and sustainable material that is growing in popularity for outdoor applications like decking, fencing, and furniture. However, left untreated, bamboo can be prone to splitting, rotting, mold growth, and sun damage when exposed to the elements. Properly sealing bamboo is crucial for protecting it from moisture, UV rays, insects, and decay so it lasts for years outdoors. This guide covers everything you need to know about sealing bamboo for exterior use.
When to Seal New and Existing Bamboo
- New bamboo should be sealed as soon as possible after installation. New bamboo has higher moisture content and is even more prone to cracking and rot if left unsealed. Seal all sides and ends.
- Existing unsealed bamboo should be sealed immediately to prevent further damage. Lightly sand to remove grime, mold, and mildew, then clean before sealing.
- Previously sealed bamboo will need to be resealed every 1-3 years as the finish wears off. Look for worn areas, cracks, peeling, etc. Sand lightly before reapplying sealer.
Sealing new bamboo right away and maintaining the finish regularly is key to making it last outdoors.
How to Prepare Bamboo for Sealing
Proper prep is vital so the sealer adheres well. Here are tips for prepping bamboo:
- Clean the surface thoroughly with a brush and mild detergent to remove dirt, debris, mold, etc.
- Rinse well and let the bamboo dry completely. Sealer won’t adhere to damp bamboo.
- Lightly sand to remove any splintered areas and smooth the surface. This gives the sealer something to grip.
- Wipe bamboo with a tack cloth to remove sanding dust before sealing.
- Apply wood filler to any cracks, holes, or imperfections for a smooth finish. Let filler dry completely.
- Use an oil-based primer on raw bamboo before sealing for best adhesion.
- Read the sealer instructions as some require wood conditioner pre-treatment.
Prepping properly will help the sealer stick, preventing peeling and having to reapply repeatedly.
Top Sealers for Outdoor Bamboo
There are many good sealing options for exterior bamboo. Here are some of the most effective:
1. Spar Urethane
Spar urethane is a top choice for sealing outdoor bamboo. It contains UV blockers to reduce fading, repels water, and resists abrasion, heat, and chemicals. Multiple coats of spar urethane will protect bamboo for years. It dries quickly and can be used on bamboo furniture, siding, and decking.
2. Marine Epoxy Resins
Two-part epoxy resins formulated for marine use offer superb protection for outdoor bamboo. The thick epoxy coating is highly water resistant and durable. Epoxy is tricky to apply evenly however and can yellow over time. It’s best for sealing rough-cut bamboo or bamboo susceptible to lots of moisture.
3. Tung Oil
Tung oil is a natural oil finish made from the nuts of the tung tree. It penetrates deep into bamboo to make it repel water and prevent moisture damage. Tung oil also enhances the natural beauty and grain of bamboo while shielding against sun damage. Multiple coats are needed for the best protection.
4. Water-Based Polyurethane
Water-based polyurethanes are easier to apply than oil-based versions with less odor and toxicity. They provide great protection for outdoor bamboo surfaces from moisture, mildew, and UV rays. Just be sure to apply enough coats to get a protective film.
5. Linseed Oil
Linseed oil derived from flax seeds soaks into bamboo and hardens to repel moisture. It contains UV absorbers to reduce sun damage but will need reapplied every year or so. Linseed oil brings out a rich luster in bamboo. Follow drying times before adding more coats.
6. Bamboo Finish Oil
Oils marketed specially for bamboo finishing penetrate deeply to protect from moisture while highlighting bamboo’s natural color. Made from tung, linseed, or other oils, they are easy to apply by brush. Reapply annually or as needed to refresh the protection.
How to Apply Sealers to Bamboo
- Read the instructions thoroughly and follow the application directions for best results.
- Use a paintbrush, roller, or rag to apply a thick, even coat over all surfaces. A pump garden sprayer also works for large areas.
- Apply sealer ends first then the sides for optimal penetration. Ends absorb the most moisture.
- Allow proper drying time between coats as specified on the can. Drying is essential for adhesion.
- Apply at least 2-3 coats for sufficient protection, adding more for high-traffic areas.
- Keep sealing until saturation; the bamboo should not absorb more.
- Lightly sand between coats to help the sealer bond.
- Maintain every 1-3 years depending on wear. Light sanding and cleaning before resealing extends the finish.
Applying sealers properly will keep your outdoor bamboo looking great for years.
Sealing Specific Bamboo Products
Sealing techniques vary slightly depending on the type of bamboo product.
Bamboo Decking
- Sweep debris and use a hose or deck cleaner to wash
- Let dry completely
- Sand smooth any splinters or rough areas
- Apply oil-based primers to unsealed bamboo decks
- Use a roller or pad applicator for even coverage
- Always do full length boards to avoid lap marks
- Choose finish with UV blockers for sun protection
- Reseal every 1-2 years
Bamboo Siding
- Clean siding thoroughly with detergent if needed
- Lightly sand any damaged areas and apply filler
- Use a pump garden sprayer to apply sealer evenly
- Focus on sealing siding ends where moisture enters
- Allow extra drying time before recoating
- Reapply sealer every 2-3 years
Bamboo Furniture
- Wipe furniture with mild soap and water solution
- Use fine grit sandpaper to smooth rough spots
- Tung oil and water-based polyurethane work well
- Apply finish along the wood grain using a clean rag
- Add extra coats to tabletops and seating surfaces
- Reseal outdoor bamboo furniture annually
Bamboo Fencing
- Use pressurized water to clean grime from fences
- Allow to dry fully before sealing
- Apply exterior stains or oils with a roller or brush
- Focus on the fence post ends in the ground
- Reseal thinner horizontal slats more often
- Refresh finish every 1-2 years for longevity
Maintaining the Bamboo Seal
To keep bamboo finishes intact for as long as possible:
- Add extra sealer to high-wear areas annually
- Watch for any cracks, peeling, dullness or erosion and reapply sealer right away
- Lightly sand then reseal any problem spots
- Clean stains from grease, food, oils quickly to prevent penetration
- Consider a water-repellent pretreatment on horizontal surfaces before sealing
With proper sealing techniques and regular maintenance, your outdoor bamboo projects will last for decades to come. Follow these best practices for keeping bamboo looking beautiful outside.
Natural Sealers for Bamboo
For a non-toxic and eco-friendly sealing option, try these natural sealers:
Beeswax and Carnauba Wax
Rubbing pure beeswax or carnauba wax (derived from palm leaves) into bamboo creates a moisture-resistant seal. The waxes penetrate into the bamboo and dry to a semi-gloss sheen. Reapply a couple times per year.
Walnut Oil
Walnut oil provides UV resistance and waterproofing. It leaves a lovely patina over time. Walnut oil is very prone to rancidity however, so purchase small bottles to use up quickly.
Hemp Oil
Hemp seed oil is an excellent sealer for bamboo surfaces. It absorbs well and dries fast to form a protective, clear coating. Reapply every 4-6 months for ongoing protection. Look for pure, food-grade hemp oil.
Flaxseed Oil
Pressed from flaxseeds, flaxseed oil penetrates deeply into bamboo while finishing with a smooth surface sheen. It shields against moisture, mold, and mildew. Reapply flaxseed oil every 3-6 months to refresh the protection.
Grapeseed Oil
Grapeseed oil is an affordable, easily absorbed bamboo treatment. It leaves a nice satin finish. Grapeseed oil does have less water resistance than some other oils, so reapply every 2-3 months.
Coconut Oil
Solid coconut oil rubbed into bamboo creates a protective finish that slowly absorbs. It repels water well due to the lauric acid content. Reapply every 3-4 months to maintain effectiveness. The coconut scent fades over time.
Beeswax Wood Conditioner
Mix equal parts beeswax and turpentine into a paste. Rub it into new, unsealed bamboo using a rag before applying your topcoat sealer. This acts as a pretreatment to fortify protection.
Pine Resin
Melted pine resin mixed with beeswax or linseed oil makes a water-resistant bamboo sealant. Slowly melt the resin first before mixing in other ingredients. One downside is pine resin can produce a tacky finish.
Milk Paint
Non-toxic milk paint containing casein protein can be used to finish bamboo surfaces. It leaves a matte, porous look however so top off with a beeswax or oil sealant for added protection.
FAQs
Does bamboo for outdoors need to be sealed?
Yes, sealing is highly recommended for all outdoor bamboo projects. Unsealed bamboo will absorb excess moisture leading to mold, mildew, splits and cracks, and eventual rot. Outdoor bamboo also needs UV protection to prevent premature aging. Consistent sealing gives bamboo used outside longevity.
How long does it take for bamboo to weather if not sealed?
On average, uncovered bamboo left continuously outdoors will start showing signs of wear within 1-2 years. Higher moisture climates will cause unsealed bamboo to weather and decay faster. Within 3-5 years, untreated outdoor bamboo will become extremely dried, cracked and faded.
What’s the best sealant for outdoor bamboo furniture?
Tung oil, spar varnish, and water-based polyurethane make excellent sealers for outdoor bamboo furnishings. They protect against sun damage, repel water, and resist surface abrasion from regular use. Reapply the finish yearly. Penetrating oils are a good choice for chairs, tables, and benches.
Can you use Thompson’s Water Seal on bamboo?
Yes, Thompson’s Water Seal is effective for bamboo outdoor applications like planter boxes, fencing, siding, and decking boards. Make sure to select the clear, waterproofer formula not the tinted wood stain options. Multiple coats are recommended for long-lasting protection.
Is tung oil good for sealing outdoor bamboo?
Tung oil is an excellent sealer choice for outdoor bamboo. When fully cured, tung oil forms a flexible, water-resistant, and UV-stable finish. Multiple thin coats allow gradual buildup for optimal protection. Reapply tung oil annually or as needed to refresh. It brings out bamboo’s inherent beauty.
How often should you seal outdoor bamboo?
On average, sealing outdoor bamboo every 1-3 years is recommended depending on usage and exposure. More frequent resealing is needed for tabletops, handrails and other high-traffic areas. Signs like peeling, erosion, and water spotting indicate it’s time to reapply the protective finish.
Can you use linseed oil on outdoor bamboo?
Yes, linseed oil is suitable for sealing outdoor bamboo. It soaks in well to repel moisture while enhancing the look of the bamboo grain. Linseed oil does need reapplied more often than other sealers – about every year for adequate protection. Make sure to let it cure fully between coats.
What is the most long-lasting sealer for outdoor bamboo?
Marine grade epoxy resins offer the most heavy-duty protection for keeping bamboo outdoors. The thick coating resists moisture, UV rays, heat, and surface abrasion better than most other sealers. Spar varnish and oil-based polyurethanes also provide long-lasting, multi-year protection.
Does sealing bamboo change the color?
Clear sealers like oils, waxes, varnishes, and epoxies will not alter the natural coloring of bamboo. Stained finishes will impart some color change depending on the tint used. A sealer may slightly deepen or enrich the shade but should not drastically change the original bamboo color.
Can you use polyurethane on outdoor bamboo?
Yes, polyurethane is an effective sealer and varnish for exterior bamboo surfaces. Oil-based polyurethane provides better protection than water-based versions. Be sure to use polyurethane containing UV inhibitors designed specifically for outdoor use. Multiple coats are recommended.
Conclusion
With proper preparation, sealant selection, application, and ongoing maintenance, bamboo can be made to last for decades outdoors. Sealing transforms bamboo from a material prone to rotting and decay into one that can withstand all the elements. Use these sealing techniques to protect your bamboo decking, fencing, siding and furniture from the effects of moisture, sunlight, insects, and weathering. With the right sealant and some periodic renewal, you can enjoy durable and beautiful bamboo projects outside your home for years to come.