Sealing outdoor wood is crucial for protecting it from the elements and ensuring its longevity. Proper sealing provides a protective barrier against moisture, UV rays, insects, and other damage. When done correctly, sealing your outdoor wood can help it last for many years with only periodic reapplication needed. This guide will teach you everything you need to know about sealing outdoor wood.

Choosing the Right Outdoor Wood Sealant

When it comes to sealing outdoor wood projects and structures, you have several good options:

Oil-Based Sealants

These penetrate deep into the wood grain and provide moisturizing as well as sealing properties. Common types are:

Tung oil – Provides a nice natural finish and water resistance. Multiple coats are needed for best protection.
Teak oil – Great for teak and other fine woods. Contains UV blockers. Requires multiple coats.
Linseed oil – Made from flaxseed oil. Has natural water repellency. Takes weeks to fully cure.
Danish oil – A blend of oils and varnish that seals, protects, and enhances wood grain. Easy application.

Water-Based Sealants

These seep into the wood and solidify to create a protective barrier. They include:

Water-based polyurethane – Acrylic-based and fast drying. Resists UV rays and provides good moisture protection.
Spar urethane – Specially formulated for outdoor use. Withstands sun, water, and temperature changes.
Exterior varnish – Contains UV absorbers. Dries slower than polyurethane but provides excellent protection.

Lacquer Sealants

Evaporate quickly to form a hard, durable, water-resistant finish:

Marine spar varnish – Exceptional protection against sun, water, and humidity. Requires fewer coats than other varnishes.
Exterior-grade lacquer – Acrylic-based for UV resistance. Multiple coats needed for best moisture protection.
High-gloss enamel lacquer – Very durable and scratch resistant once cured. Ideal for items like outdoor furniture.

Epoxy Resins

Offer the most complete and long-lasting wood sealant protection:

Polyurethane casting resin – 100% waterproof with superior UV resistance. Used for decorative coatings.
Marine epoxy – The gold standard for waterproofing, strength, and resistance to abrasion. Ideal for boats and docks.
Tabletop epoxy – Gives an ultra clear, glass-like finish for bar tops, tabletops, etc.

Prep Your Wood Before Sealing

Proper prep work is vital for the sealant to adhere correctly and provide maximum protection:

Clean Thoroughly

Remove all dirt, dust, grease, wax, mildew, or existing failing sealant
For cleaning, use mild soap and water, denatured alcohol, or ammonia
Rinse off any cleaner residues thoroughly

Sand Lightly

Use 120-150 grit sandpaper to scuff up the surface
Helps sealant penetrate and improves adhesion
Be careful not to expose new raw wood

Allow to Dry

Let the wood dry out completely before sealing
Moisture trapped under the sealant can cause problems
Allow at least 24-48 hours for thorough drying

Apply Wood Conditioner

Using a pre-seal wood conditioner helps regulate moisture absorption
Evens out porous areas and prevents blotchiness
Lets you achieve a more uniform sealed surface

How to Apply an Outdoor Wood Sealant

Follow these steps for a smooth, effective sealing application:

1. Plan Your Coats

Read the product directions to determine how many coats are needed
Oil-based sealants require more coats than water-based ones
Allow proper drying time between coats

2. Stir the Sealant

Stirring blends the ingredients smoothly for an even coat
Makes sure pigments are evenly dispersed throughout

3. Use a Good Brush

Use high-quality brushes made for oil-based or water-based sealants
Disposable foam brushes work for oil-based sealants
Avoid cheap brushes that can leave behind bristles

4. Load the Brush Properly

Don’t overload it – excess sealant leads to drips and sags
Dip halfway into the can and tap lightly against the side

5. Apply Even Coats

Work evenly and gently to spread the sealant smoothly
Go with the wood grain direction for best results
Allow time between coats for drying

6. Cover All Sides

Fully coat all surfaces – front, back, edges, and ends
Don’t miss any crevices, holes, or hidden sides
Protect decorative carvings and details thoroughly

7. Work in Good Conditions

Seal when the temperature is between 50-90°F
Avoid sealing in direct sunlight or on hot surfaces
Wind and dust can affect the final cured surface

8. Allow Proper Curing Time

Most sealants take 24-48 hours for one coat to fully cure
Curing takes longer in cold, damp, humid conditions
Don’t replace outdoor furniture or walk on sealed decks until fully cured

How Often to Reapply Outdoor Wood Sealant

On decks, fences, siding – every 1-2 years
On outdoor furniture – every 1-3 years
High-traffic areas may need sealing annually
Reapply when you notice fading, cracking, or peeling

Watch for signs like water beading up rather than absorbing to know when it’s time. Harsh weather and sun exposure will require more frequent resealing.

Sealing Different Types of Outdoor Wood

Certain wood species and products need special sealing considerations:

Cedar and Redwood

Contain natural oils that resist moisture – don’t require much sealer
A weatherproofing stain or light sealant helps maintain color

Pressure-Treated Wood

Let it dry out for several months before sealing
The chemicals used to treat it can interact with certain sealants

Plywood

Its laminated construction can react with some film-forming sealants
Oil-based sealants recommended to allow for expansion/contraction

Log Homes or Timbers

Use highly elastic sealants that won’t crack as wood shifts
Saturate end grains extra well to prevent moisture ingress

How to Seal Wood Furniture for Outdoor Use

Outdoor wood tables, chairs, benches, etc need proper protection:

Lightly sand to improve adhesion and apply wood conditioner
Use oil-based sealants like tung oil or spar varnishes for protection
Teak oil helps maintain the natural look of teak furniture
Reseal furniture every year or when water stops beading up
Epoxy resin can provide the most heavy-duty coating for bar tops and tables

FAQs About Sealing Outdoor Wood

Does the wood have to be bare before sealing?

Previously sealed or finished wood needs to be stripped down to bare wood again before applying a new sealant.
This ensures proper adhesion. Use a chemical stripper or power washer to remove old sealant.

Should I use a sealant or a stain on outdoor wood?

Deck stains help protect and beautify but don’t waterproof as well as true wood sealants.
For optimal protection, use a sealant first followed by an exterior-grade stain.

What mistakes should I avoid when sealing outdoor wood?

Skipping proper surface prep
Applying in direct sunlight or on hot surfaces
Not allowing proper drying time between coats
Not stirring the can thoroughly before use
Using poor quality brushes that leave behind bristles

Why does my sealed outdoor wood look dull and faded?

Outdoor sealants degrade over time due to sun exposure and weathering.
This is normal wear. Simply clean the wood thoroughly and reapply fresh coats.

What’s the difference between varnish, polyurethane, and lacquer?

Varnish has a longer oil base for deeper penetration. Polyurethane dries faster and resists abrasion. Lacquer dries the quickest for multiple coats in one day.

Conclusion

When sealing any outdoor wood project, the key steps are proper surface prep, choosing the right sealant, following application directions, allowing for full cure time, and periodic reapplication. Oil or water-based formulas as well as marine epoxies and varnishes are all good options. With the right sealant and some periodic upkeep, your outdoor wood projects can maintain their beauty for years to come against the effects of sun, rain, and weather. Follow this guide to get the most longevity out of fences, decks, furniture, and any other outdoor wood.

How to Seal Wood for Outdoor Use