How To Seal Painted Wood For Outdoor Use

Last Updated on April 28, 2023 by Ernest Godia

While you may not permanently prevent outdoor wood from weathering, you can apply a sealant to guarantee longevity.

Painting is one way to protect outdoor wood from the elements and make it more durable. Once you choose this option, you may have to repaint your wood occasionally or as the seasons change.

However, sealing painted wood is a life-changing hack that makes the painted outdoor wood durable and helps retain its aesthetics.

This article looks at how to seal painted wood for outdoor use to guarantee longevity. You will also learn the instances where sealing painted wood is necessary and how to choose a sealant for this project. 

How To Seal Painted Wood For Outdoor Use

Outdoor wood tends to weather with exposure to the elements, heat, moisture, and mechanical force. Evidence that your outdoor wood is weathering, you’ll notice a change of color on your fence, mailbox, or furniture placed on the patio, deck, porch, or backyard.  

Most exterior paints contain chemicals that make them waterproof and immune to extreme weather changes. However, some paints are susceptible to peeling, fading, or discoloration. Adding a coat of exterior-grade sealant can help prolong the life of the finish.

Ready to learn how to seal painted wood for outdoor use? Read along.

What you will need to complete this project   

  • Tack cloth or rag
  • Sandpaper
  • Applicator (Paintbrush, sponge, or roller)
  • Paint thinner or mineral spirits
  • Trisodium phosphate (TSP)
  • Protective gear
  • Your choice of sealant
  • Latex or rubber gloves
  • Stir stick

Below is a step-by-step guide detailing how to seal painted wood for outdoor use:

STEP 1: Choose the appropriate sealant

Since you are working on an outdoor project, ensure the sealant you choose is specifically formulated for exterior use. Using a product formulated for indoor use outside will not work.

When choosing your sealant, also consider the following factors: 

  • The type of paint coat on the wood (the paint must be compatible with the sealant) 
  • Durability
  • Cost 

STEP 2: Clean the painted wood surface 

After picking your preferred sealant, it’s time to prep the painted surface.

Mix the trisodium phosphate (TSP) with warm water in a clean container or bucket. Put on your gloves and saturate a rag or sponge with the solution.

Squeeze out the excess liquid until the cloth or sponge is only damp and not wet. The aim is to clean your painted surface, not to soak it up. 

Remove any dirt, oils, and stains off the painted surface by wiping it with the damp cloth.    

Some states have banned the use of phosphate-based detergents like TSP. If that law affects you or you are trying to avoid using phosphates, the TSP substitute is an excellent alternative. Mix and use the substitute like you would TSP.  

STEP 3: Prepare the sealant

Prep the sealant by mixing the pigment and binders that might have settled at the bottom of the container. To do this, use a wooden stirring stick to gently but thoroughly stir the product until it is consistent.

It is essential to stir gently to avoid introducing air bubbles.

Carefully read the manufacturer’s instructions. Some sealers need you to follow specific instructions.

STEP 4: Lightly sand the painted wood surface

Lightly sand the painted wood surface to remove any rough spots, splinters, or stains. Use fine-grit sandpaper, preferably 220-320 grits.

When sanding, don’t press too hard or scuff too harshly. You’ll risk sloughing or peeling the paint off.

Ensure the surface is dry. If it isn’t, you can give it a day before proceeding.

STEP 5: Remove the dust

Wipe off the sand dust with a tack cloth or blast of air. Particles will affect how well the sealant bonds to the painted wood surfaces. 

Sealing with sanding dust or dirt particles underneath creates a bumpy, unsightly surface.

STEP 6: Apply the sealer 

Once the surface is clean and dry, dip one-third of your brush into the prepared sealant. Don’t wipe off the excess on the ends of the container to prevent the formation of bubbles. Instead, tilt the brush and let the excess sealant drip off.

In sweeping strokes, apply the sealant from one edge to the other along the direction of the wood grain. Remember to keep a wet edge and paint forward to smooth out bubbles or drips quickly. 

Don’t over-brush, as that creates bubbles and makes your brush sticky.

Apply a thin and even coat of sealant and let it dry according to the manufacturer’s instructions. 

STEP 7: Sand the cured sealant 

The time taken by each sealant to cure varies because some are quick-drying, like polyacrylic, and others, like polyurethane, take at least 24 hours to cure.

Sand between coats as you let the sealant dry before applying another layer. Use an electric sander with fine-grit sandpaper.

What happens if you don’t sand between coats of polyurethane? Read our article to learn the details. 

STEP 8: Remover the sealer’s sanding dust

Sand the coat after it has cured into a hard finish. Clean off the dust on the surface with a tack cloth, vacuum, or clean rag.

STEP 9: Reapply the sealer and let it dry

Add another coat of sealant for better adhesion and durability.

Let the sealant dry as per the manufacturer’s instructions. If the drying time isn’t indicated, let the furniture stand overnight for an excellent finish.

How to seal painted wood for outdoor use

How to choose the right product for sealing painted wood for outdoor use

Here is what you ought to consider when choosing a sealant to apply over painted outdoor wood:

1. Type of paint on the wood 

The type of paint coat on the wood will dictate the suitable sealant for your project. Some outdoor paints are designed to withstand the elements, heat, and heavy traffic. Other paints require a sealant to extend their lifespan.

2. Adhesion 

Check if the sealant is compatible with the paint before using it on your project. Oil-based paints bond better with solvent-based sealants, while water-based sealers adhere better to acrylic and latex paints.

3. Durability 

A suitable wood sealant helps prolong the life of the paint and slows down the wood weathering process.

In most cases, oil-based sealants like exterior oils and polyurethane provide more extended protection than water-based sealants. Overall, epoxy and polyurethane are still the kings of outdoor sealants.

4. Toxicity

Some sealants have highly toxic fumes. For example, oil-based polyurethane contains a high level of volatile organic compounds, making it toxic. So, too, are cleaners like trisodium phosphate, or TSP.

When working with such chemical products, it is best to wear protective gear, including a respiratory mask and eye protection. In addition, your work area needs to be well-ventilated and properly dispose of the products you use.

Remember to clean the brushes used with mineral spirits or paint thinner and have them ready for the next project.

Products To Use When Sealing Painted Wood For Outdoor Use

The market is flooded with various sealers for painted wood for outdoor use. After extensive research, we have picked out five products that make excellent sealants on painted wood for outdoor use:


Polycrylic is water-based and will only bond to water-based paints. It contains polyurethane resins, making it resistant to moisture, heat, and abrasions.

Polycrylic has less pungent and toxic fumes than polyurethane. In addition, it is quick-drying and easy to apply, giving your furniture a clear, satin, or high gloss finish. Due to its thin nature, you’ll have to use more layers for a better outcome.

Polycrylic is not the most durable exterior-grade sealant, so consider using it only for painted wood in sheltered outdoor areas for better durability. 


Polyurethane is available in oil- and water-based forms. When sealing oil-based painted surfaces, use a solvent-based poly, and apply water-based polyurethane on latex or acrylic paints. 

Be careful to distinguish the two because using incompatible products will be a waste of money and the product.

Polyurethane takes longer to dry. It gives painted wood a shiny finish.

Exterior Oils 

Exterior oils like Danish, coconut, tung, teak, and linseed oils are popular.

Manufacturers now combine different oils with mineral spirits and additional components to create the perfect wood sealant for painted wood for outdoor use.


Epoxy is an excellent sealant that leaves a non-porous coat on painted wood surfaces. Despite how pricy epoxy is, it offers protection against the elements, heat, and heavy traffic. The protective film of epoxy can last 5-10 years.

Here is an in-depth comparison of epoxy and polyurethane. Enjoy!

Paint and sealer combinations 

There is a fuss about the sealer combos. This new product combines paint and sealant in a single can. The sealer combos dry clear, making them ideal for white-painted surfaces.

The paint and sealer combinations don’t need additional toppings for extra protection. The product comes with instructions on how to prepare and apply it. You should read and follow the instructions to avoid messing up your project.  

Reasons For Sealing Painted Wood For Outdoor Use

A wood sealer comes in handy in any painting project, irrespective of whether it is indoor or outdoor wood. Sealants protect the wood from moisture and sunlight and preserve its natural allure.

Below are reasons why a sealant will benefit your painted outdoor wood:

  • Some paints are prone to peeling, discoloring, and fading over time. A sealant works as a barrier between the painted wood and external elements, just like sunscreen to the skin.
  • Sealing outdoor painted wood surfaces helps reduce the rate at which it weathers and prolongs its life.
  • Sealants protect painted outdoor wood from abrasions, mechanical damage, and wear and tear.
  • Applying a sealer slows down paint decay.
  • It helps the wood preserve its beauty.

When To Seal Painted Wood For Outdoor Use

If you look at your outdoor furniture and notice the paint has faded and lost its gloss, it’s time to apply a sealant.

Painted outdoor wood is predisposed to photo-degradation. Photo-degradation is when the paint molecules lose their adhesion and protective bond. Some of the components in paint absorb sunlight’s UV rays and speed up paint decay.

Get your sealants and brushes ready when you notice the paint has lost its original color, shine, appeal, and elasticity. 

Here are other conditions under which you’ll need to seal painted wood:

  • To add a tone to the existing paint job. Sealants can give paints an amber or sepia tone.
  • To add life to distressed or weathered wood.
  • To increase paint durability
  • When you notice the presence of mildew on the wood, water makes wood a haven for fungi which multiplies and eventually damages the wood. 

When To Avoid Sealing Painted Wood For Outdoor Use 

Some exterior-grade paint and paint sealer combos don’t need an additional coat of sealant for protection. Applying 2-3 coats of exterior paint is sufficient for outdoor protection.

If the exterior paint needs a redo, add another layer or two of the same paint, and the painted wood regains its glow.

When feeling exploratory and deciding to apply a clear-coat painted wood, keep in mind that the exterior paints contain sealants and that some paints will, in turn, change color. It is best to experiment on a less conspicuous part of wood before you ruin the entire painted surface.   

An alternative to wood sealant is applying a powder coat on the surface. Powder coating provides better heat resistance and is durable and beautiful. In addition, powder coating is available in multiple colors to blend with your style. 

How To Seal Painted Wood For Outdoor Use: FAQs

Here are the answers to some of the commonly asked questions about sealing painted wood for outdoor use:

Do you need to seal the painted wood outside?

Yes and no!

Some paints, like latex and acrylic paints, need a sealant to act as a protective barrier between the painted wood and external factors.

Sealing some paints can result in color change. Exterior paints already contain sealants, so you don’t need to add an extra coating. However, if you feel a sense of adventure and decide to add a clear sealant over the paint, test it out on an inconspicuous part first.

Can you seal the wood after painting?

Yes, you can. Applying a sealant on a painted wood surface reduces its chances of mold and mildew infestation. It also acts as a protective barrier against the elements and prevents yellowing, cracking, and peeling.

Wait at least 3-4 days before adding a coat of sealant to a freshly painted piece. Follow the manufacturer’s instructions for the correct mix ratio and application technique of the sealant. 

How To Seal Painted Wood For Outdoor Use: Final Thoughts  

There mustn’t be more than a paint job to protect outdoor wood from the elements. However, adding a sealant can help postpone the painted wood damage to a later date.

We have gathered the necessary information you might need in your sealing project. We take great pleasure in making your project a success, and we hope this guide helps make that happen.

As you embark on your new project of sealing painted wood for outdoor use, please share your experience with us in the comments.

Happy sealing!

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