Once you know how to waterproof wood, your wood will look beautiful and remain in top condition for the long term. Waterproofing wood protects the wood with liquid sealants and coatings that fill and top the wood's cells to create a hardy structure that stands up to water in all its forms. As a bonus, waterproofing wood strengthens it against surface wear. Some coatings have additives to guard against fading and sun damage.
Before You Begin
Choose a synthetic sealant, a natural oil, or a stain/sealer to waterproof the wood. Each has its own waterproofing profile, ease of use, and durability expectation.
Synthetic Sealants
Sealants applied to the surface of the wood soak in to firm the wood's cellular structure. Additional coats of sealant build the coating to the top, forming an impermeable barrier against water penetration. The water cannot damage the wood because the water is never given a chance to contact the wood. Sheens range from satin to high-gloss.
- Varnish: Varnish gives the wood a tough, shell-like finish that resists yellowing, and which works well for outdoor use because it filters out harmful UV rays.
- Lacquer: Lacquer imparts a deep tone to the wood, but it will yellow over time.
- Polyurethane: Polyurethane sealants, available in both water- and oil-based versions, are popular wood finishes because they are easy to work with and resist yellowing.
Natural Oils
Natural oils applied to the surface of the wood soak in deeply, eventually hardening within the wood's cells. Oils are considered to be penetrative sealers: They remain in the wood but not on top of the wood. Oils maintain wood's natural look and tactile quality. So, the wood continues to feel like wood, not like coated wood.
Natural oils for waterproofing wood include linseed oil, tung oil, and Danish oil. Danish oil is a blend of tung oil and varnishes. Oils can be brushed on or wiped on with a cloth. Oils have a short re-coat time and are usually ready to be touched soon after.
Tip
Waterproofing oils need to be reapplied more frequently than synthetic sealants—up to twice a year, depending on the wood and surrounding conditions.
Stain/Sealer Combinations
Stain/sealers are exterior wood stains that contain wood sealers. Stain/sealers typically come in a range of wood-friendly colors like browns, tans, and reds. These products are mainly used for outdoor elements like decks, fences, siding, shingles, outdoor wood furniture, and railings.
Stain/sealers can be brushed on or wiped on. Due to the larger scale of the items stain/sealers are meant to protect, most are rolled on or sprayed with airless paint sprayers.
Tip
Stain/sealers are meant to protect wood under the harshest conditions, so many come with a host of additives, including UV protectants and mild and mildew blockers.
When to Waterproof Wood
All waterproofing products require the wood to be completely dry before application. Applying the coating over wet wood will trap the moisture in the wood, especially with sealants. When waterproofing new wood, test the wood with a pin-type moisture meter. Wait until the wood's moisture content has reached 12 percent or less.
Do not apply wood waterproofing products in direct sunlight. The temperature should be between 55 to 90°F, with a relative humidity level of less than 85 percent.
Safety Considerations
Work in a well-ventilated area. Wear a NIOSH-approved respirator if there are ventilation concerns.
What You'll Need
Equipment / Tools
Sealant Method
- Nitrile waterproof gloves
- Synthetic bristle brush, foam brush, or applicator pad
- Tack cloth or shop vacuum
Oil Method
- Clean, lint-free rags
- Staining pad
- Nitrile waterproof gloves
- Tack cloth or shop vacuum
Stain/Sealer Method
- 3/8-inch nap roller, nylon/polyester brush, pad applicator, or an airless sprayer
- 5-gallon bucket
- Nitrile waterproof gloves
- Tack cloth or shop vacuum
Materials
Sealant Method
- Sealant
- Mineral spirits or paint thinner
Oil Method
- Tung, linseed, or Danish oil
- Mineral spirits or paint thinner
Stain/Sealer Method
- Stain/sealer
- Mineral spirits or paint thinner
Instructions
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How to Prepare Wood for Waterproofing
For any waterproofing method, prepare the wood the same way:
- Remove paint and other coatings down to bare wood with sandpaper or strippers.
- For stain/sealers, pressure wash the deck, fence, or railings with a pressure washer on a broad spray pattern.
- Sand the surface with a series of sandpaper grits, starting with coarse grits and working down to fine grits.
- Clean the wood of sanding dust with a vacuum, tack cloth, or a cloth soaked in mineral spirits.
- Strip problem substances like grease with mineral spirits.
How to Waterproof Wood With Synthetic Sealants
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Mix the Sealant
Stir the sealant gently with a paint stirring stick in a separate container. Do not shake or slosh as this will create bubbles.
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Apply the Sealant
Apply the sealant to the wood with a synthetic bristle brush, foam brush, or applicator pad.
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Let the Sealant Dry
Let the sealant wait for its entire re-coat time or longer before applying the next coat. The re-coat waiting period for water-based polyurethane is two hours or more. For oil-based polyurethane sealant, the re-coat time is four hours or more.
Tip
Assist drying times by keeping the room warm and well-ventilated but dust-free.
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Lightly Sand
If the surface of the wood is raised at the end of the re-coat time, lightly sand the wood with #220 to #320 grit sandpaper. Wipe clean with a tack cloth.
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Apply Multiple Coats of Sealant
Apply two or three more coats of sealant. The sealant should form a build on the wood, with none of the wood grain exposed.
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Clean Tools
With water-based sealant, clean tools with warm water and soap. With oil-based sealant, clean with mineral spirits or paint thinner.
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Wait Until Use
Wait up to three days for the wood to be ready for use.
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How to Waterproof Wood With Natural Oils
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Mix the Oil
Mix the oil in a separate container with a paint stirring stick. You can also mix the oil in its own container by sloshing it gently and then allowing 15 to 20 minutes for bubbles to disappear. Do not shake vigorously.
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Apply the First Coat
Brush or wipe the first coat of oil onto the wood with a brush, applicator pad, or a lint-free cloth. Apply the oil in the direction of the wood grain. Be careful not to over-apply the oil, as this will cause it to pool up.
Tip
Keep the room clean and dust-free during the entire oil application process. Dust will cling to the oil before it has fully hardened.
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Let the Oil Penetrate
Let the oil soak into the wood for about 15 minutes.
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Wipe the Surface Clean
Using a fresh towel, wipe the entire surface in the direction of the grain to even out the oil and remove pools. Keep the pressure gentle. Removing excess oil is one of the most important steps in working with oil because it improves drying time and prevents the wood from developing a spotty appearance.
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Reapply the Oil
If another coat of oil is needed, apply it with a fresh cloth. Let the oil sit for 15 minutes, then wipe clean.
Tip
With oils, it's best to keep it light. One or two coats are sufficient. Too many coats will make the surface look dirty and cloudy.
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Clean Tools
Clean brushes and other tools with mineral spirits or paint thinner.
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How to Waterproof Wood With a Stain/Sealer
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Mix and Box the Stain/Sealer
Combine several separate containers of stain/sealer in a larger container (five gallon bucket) for color consistency. Stain/sealers are heavy with pigment, so make sure that the product is well-mixed.
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Apply the Stain/Sealer
Apply the stain/sealer to the wood with a 3/8-inch nap roller, nylon/polyester brush, pad applicator, or an airless sprayer. Apply a thin coat. Work quickly but carefully, so that you'll always be working with a wet edge.
Tip
If the wood was pressure washed, wait at least 24 hours for the wood to fully dry before sealing it.
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Wait for the Stain/Sealer to Dry
The re-coat time for water-based stain sealers is one to two hours. For oil-base stain/sealers, the re-coat time is a minimum of two to four hours.
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Apply a Second Coat
Brush, roll, or spray on a second coat of stain/sealer. Like the previous coat, keep it thin and light. Two coats are sufficient for stain/sealers. Wait two to three days before using the wood item.
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Clean Tools
Clean brushes, paint sprayers, and other tools with mineral spirits or paint thinner for oil-based stain/sealers. Water-based products clean up with water and mild soap.
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FAQ
Can you make wood 100-percent waterproof?
You can make wood 100-percent waterproof by completely saturating the wood with a sealant and building up the product so it forms a hard shell.
How many coats of polyurethane does it take to waterproof?
Three to four coats of polyurethane are needed to waterproof wood. Water-based polyurethane will require several more coats than oil-based polyurethane.
What is the best outdoor wood protection?
Stain/sealers that contain both wood stain and wood sealers are designed for outdoor wood protection. They are the best protection for most applications.
5 Best Wood Deck Board Materials
As a seasoned expert in woodworking and wood preservation, I bring a wealth of hands-on experience and in-depth knowledge to guide you through the intricacies of waterproofing wood. Over the years, I've honed my skills in selecting the right sealants, oils, and stain/sealer combinations to enhance the beauty and longevity of wood structures, be it decks, furniture, or outdoor elements.
Understanding Waterproofing Options:
1. Synthetic Sealants:
- Varnish: Provides a tough, shell-like finish resistant to yellowing, making it ideal for outdoor use.
- Lacquer: Imparts a deep tone but tends to yellow over time.
- Polyurethane: Water- and oil-based options that are popular for ease of use and resistance to yellowing.
2. Natural Oils:
- Linseed Oil, Tung Oil, and Danish Oil: Penetrative sealers that maintain the natural look and tactile quality of wood.
- Application: Can be brushed or wiped on, with a short re-coat time, usually ready to touch soon after.
3. Stain/Sealer Combinations:
- Purpose: Designed for outdoor elements like decks, fences, siding, and furniture.
- Colors: Come in wood-friendly shades like browns, tans, and reds.
- Additives: Many contain UV protectants and mildew blockers for added durability.
When to Waterproof Wood:
- Dry Wood: Ensure the wood is completely dry before applying any waterproofing product.
- Moisture Content: Use a pin-type moisture meter; apply when the wood moisture content is 12% or less.
- Temperature: Apply in temperatures between 55 to 90°F, with humidity below 85%.
Safety Considerations:
- Ventilation: Work in well-ventilated areas.
- Respirator: Wear a NIOSH-approved respirator if ventilation is a concern.
Materials and Tools You'll Need:
- Synthetic Sealant Method: Nitrile waterproof gloves, synthetic bristle brush, foam brush, or applicator pad, and mineral spirits or paint thinner.
- Oil Method: Clean, lint-free rags, staining pad, and mineral spirits or paint thinner.
- Stain/Sealer Method: 3/8-inch nap roller, nylon/polyester brush, pad applicator, or an airless sprayer, 5-gallon bucket, and mineral spirits or paint thinner.
Step-by-Step Instructions for Waterproofing:
- Preparation: Remove coatings, sand, and clean the wood thoroughly.
- Synthetic Sealants: Mix, apply, let dry, sand if needed, apply multiple coats, clean tools, and wait for use.
- Natural Oils: Mix, apply the first coat, let penetrate, wipe clean, reapply if necessary, and clean tools.
- Stain/Sealer: Mix and box, apply, let dry, apply a second coat, clean tools.
FAQ:
- Making Wood 100% Waterproof: Achieve this by saturating the wood with a sealant and building up layers to form a hard shell.
- Coats of Polyurethane: Three to four coats are needed for waterproofing wood. Water-based polyurethane may require more coats than oil-based.
- Best Outdoor Wood Protection: Stain/sealers that combine wood stain and sealers are optimal for outdoor applications.
By following these comprehensive guidelines, you'll ensure the effective waterproofing of your wood, enhancing its beauty and ensuring long-term durability.
