Painted Wood for Outdoor Use

How to Seal Painted Wood for Outdoor Use

In Exterior Wood, Tips by Jamie

If you have painted wooden fixtures in your yard, you may be thinking about sealing them to give extra protection. Although not always necessary, this is a good way to improve the longevity of the paint.

Using 2-3 coats of spar urethane or exterior polyurethane is the best way to seal painted wood for outdoor use. Other products can be effective, just stick with oil-based sealers and always use specific exterior products.

It is important to know when it is right to seal exterior painted wood and what products you should use. This guide will tell you everything you need to know. 

Does Painted Wood for Outdoor Use Need to Be Sealed?

No, most painted wood does not need to be sealed, even if you are using it outdoors. Exterior paints are designed to protect against weather elements, including rain, snow, sun, and temperature changes. Weather-resistant paints usually contain UV protection ingredients to keep the color from fading over time too. Think of paint for siding, for example.

The instructions don’t say paint and then apply sealer because the paint itself is strong enough to form a protective bond against the elements. A good exterior paint, when applied properly, can last for decades in ordinary conditions.

However, there are some situations when using a sealer can be a good idea if you want to protect painted wood.

When Can Clear Coats Be Used on Exterior Painted Wood?

Clear coats can be used to offer extra protection and stop the paint from peeling and chipping when exposed to the elements. Garden furniture or doors, for example, may need to be sealed. Arbors and other wooden garden features may also benefit from a clear coat because they are constantly exposed to moisture and dirt. Boats are also given a clear coat, in many cases, because they are sitting in the water and they need as much moisture protection as possible.

That doesn’t mean that exterior paint does not offer enough protection because it does, as long as you use good quality products. But if you want to be extra sure, you can use a clear coat to give you an added layer of protection and prolong the life of the paint.

How to Seal Painted Wood for Outdoor Use (Step-by-step)

Applying a few coats of spar urethane or exterior polyurethane can protect the paint for longer and stop moisture from damaging it. Just keep in mind that spar urethane will turn yellow over time if used on a white or light colored paint. So, it is best avoided if you have used chalk paints on furniture, for example.

If you want to seal painted wood for outdoor use, follow these key steps:

  1. The first thing you need to do is clean the surface from dust and dirt. If there’s any old paint, you can scrape it off with a wire brush or steel wool before you start cleaning the surface.
  2. Apply a coat of exterior primer if your wood is bare or if the existing paint has started peeling and flaking.
  3. The next step is to apply two coats of exterior paint, whether it’s oil-based or alkyd enamel. Oil-based paints are usually more durable so they tend to give better results in the long term.
  4. After the paint has dried thoroughly, apply a coat of spar urethane or exterior polyurethane with a brush or roller. Two coats are generally enough to protect your painted wood well but feel free to use three if you need better protection against the elements.

That’s it! If you follow these key steps, your painted wood should hold up for years outdoors without peeling or chipping.

What Types of Wood Sealers are Available for Outdoor Use?

Spar Urethane Rust-Oleum 250241 Diamond Spar Urethane Satin

Spar urethane is a protective wood sealer that’s used to waterproof, stain, and enhance the appearance of wooden decks, fences, and garden furniture. It comes in oil-based or water-based formulations. It’s very durable and long lasting, and it’s easy to apply and gives excellent results. It also offers great UV protection, which means it can protect the surface from fading over time.

Exterior Polyurethanes

Polyurethane is a wood sealer that protects the wood from moisture, fading, and discoloration. It also comes in water-based or oil-based options (use oil-based for exterior painted wood). It’s easy to apply and offers high levels of UV protection as well as color stability. Specific exterior polyurethane products are available for different types of wood, such as cedar and redwood. It gives excellent protection to wood once painted but can be used to protect unpainted wood too.

Wood Oils

Hope's Pure Tung Oil, Waterproof Natural Wood Finish and Sealer, 32 Fl Oz

Wood oils are a common choice for protecting wood. They penetrate deep into the surface and nourish, waterproof, and protect it from fading or discoloration. They’re easy to apply with a pad or brush and give you a natural-looking finish that’s suitable for garden furniture, planters, fences, and decks. However, wood oils are not recommended for painted wood as they cannot soak into the wood properly.

RELATED: How to Treat Untreated Wood for Outdoor Use

Wood Sealers to Avoid Outdoors?

Polycrylic or Water-Based Polyurethane

Polycrylic and water-based polyurethanes are not suitable for exterior wood surfaces because they tend to peel off when exposed to the elements. They may work fine indoors but they are not recommended for outdoor use because their performance declines much faster if exposed to the sun, rain, snow, etc. Always stick to oil-based products when working outside.

Furniture Wax

Furniture wax is often used to give a nice finish and protect furniture. However, it is not effective when used on exterior painted wood. The wax needs to penetrate deep into the wood to protect it, and it is not able to do this if the wood has been painted. There are specific exterior furniture wax products available, but they are only good for bare wood surfaces.

Shellac

Shellac is one of the worst choices for outdoor projects because it doesn’t like moisture. As soon as it gets wet, the surface will go a cloudy white color. This may disappear when it gets warm and dries out again, but this will continue happening and completely ruin the appearance of the wood.

Shellac can also trap moisture under the surface, so the paint starts to peel and bubble in no time at all. So, unless you want to ruin the paint, avoid shellac.

Lacquer

Lacquer is another finish that’s not suitable for exterior projects. It doesn’t like moisture or changes in temperature, so it can peel off the wood in no time when exposed to the elements.

Any Other Interior Finishes

As a general rule, any interior finishes should be used for exactly that – interior projects. There’s a reason that there are separate products for interior and exterior use. Those that are designed for outdoor use give a much better seal and offer superior protection.

painted wood outdoors sealed

What Makes a Sealer Rated Outdoor Use?

Extra Protection

Typically, exterior wood sealers are formulated to withstand more conditions than interior products. The manufacturers know that the wood will be exposed to rain, snow, sun, high humidity levels, heat, etc., so they make sure their products are vastly superior in terms of quality and durability. They often give more protection against general wear and tear from foot traffic or being moved around etc, which is why they are more effective for things like decking and outdoor furniture. They also tend to last longer than interior finishes.

Seals from Water and Moisture

Moisture is the number one problem with wood outdoors. It causes mold, rot, and discoloration so it’s important to seal outdoor projects properly, or else they won’t look good for long. Exterior wood surfaces need to be sealed against moisture so water cannot penetrate deep into the surface layers. The exterior finishes are formulated to create a barrier and prevent water from soaking the wood.

Prevents Mold and Mildew

Exterior wood sealers also protect against mold and mildew. These can damage the wood if left untreated, so it’s important that any exterior surface has been treated with a moisture-resistant sealer. Specially formulated sealers for outdoor use can also include specific mildewcide chemicals to kill off mold and mildew spores and prevent them from growing.

UV Protection

Exterior wood surfaces are exposed to sunlight on a daily basis so they need extra protection. The exterior finishes that are made for outdoor use usually contain some form of UV-resistant chemicals that protect the wood against damage from ultraviolet light. This is an important feature because untreated, the sunlight will cause the wood surface to fade and lose its color. This is a significant benefit if you are using a sealer on painted wood because it will hold its color for much longer than it would if it were not protected against UV rays.

Related Questions

Can You Mix Paint and Sealer Together?

Mixing paint and sealer will cause problems because they are not compatible. The exterior finishes are formulated with specific components carefully checked to make sure they work together properly. If you pour an interior finish on top of an exterior finish, it will cause the two liquids to separate inside the container.

Once the paint is dried and the chemical reactions have finished, it is then safe to apply the sealer over the top. But if you do it while wet, the two will react.

How to seal acrylic paint on wood for outdoors?

If you want to seal acrylic paint on wood outdoors, then the best solution is exterior-grade polyurethane. It will resist any moisture from penetrating into the surface and offer an extra layer of protection against scratching and abrasion.

Start by applying the acrylic paint according to the manufacturer’s instructions. Make sure that you let it fully dry before applying two or three coats of polyurethane, giving it time to dry between each coat.

However, keep in mind that acrylic paint already forms a good protective layer and is designed for outdoor use. So, you may not need to seal it in the first place.

Can You Apply Thompson Water Seal Over Paint?

This depends on the type of paint that you are using. If you are using water-based or latex paints, you need a water-based sealer, so Thompson’s Water Seal is not the best option. However, it does work well on oil-based paints. But bear in mind that Thompson’s Water Seal is designed to soak into the wood and offer protection, so if the surface is painted it is less effective at protecting against moisture. If possible, it is better to use spar urethane or exterior polyurethane.

Can You Apply Minwax Polycrylic for Outdoor Protection?

Polycrylic is not as durable as polyurethane or spar urethane, so it is not a good option for exterior use. It works well indoors to protect against spills and stains but is not a durable finish for outdoors where the UV rays will break down the chemical compounds found in the product.

Can I Use Interior Paint on Exterior Wood?

Interior paints can technically be used on exterior wood, but it’s not a good idea. They are not designed to stand up against the elements and exposure to UV rays and moisture will cause the color to fade and chip off. If you want full protection, use exterior paint for the best results. It’s what it was designed for.

Does a Painted Deck Need to be Sealed?

A painted deck does not necessarily need to be sealed, but it does give more protection, especially in high-traffic areas. Spar urethane is the best choice for painted decks, but you can also explore specific deck sealer products too. Just bear in mind that many of these are designed for decks that have not been painted.

How Do You Seal Painted Rocks?

The easiest way to seal painted rocks is to use a spray sealer. Many acrylic paints are self-sealing, so you don’t need to bother with another sealer. But if you do decide to seal them, a spray can of general-purpose gloss or stain sealer will work well.

Final Thoughts

Sealing outdoor painted wood is a good way to improve the longevity of the paint and prevent fading from sun damage. In most cases, spar urethane or polyurethane are your best options. Just make sure that you always use products that are specifically formulated for outdoor use so you get the protection you need.

About the Author

Jamie

Jamie is the founder of The Backyard Pros. When he was 15 years old he started working at a garden centre helping people buy plants, gardening products, and lawn care products. He has real estate experience and he is a home owner. Jamie loves backyard projects, refinishing furniture, and enjoys sharing his knowledge online.