How to Seal Painted Wood for Outdoor Use? (4-Steps)

Painted wood gives a beautiful and natural feel but the problem with paint on outdoor wood is that the wood will be exposed to harsh elements. So how do you seal painted wood for outdoor use?

You can seal painted wood for outdoor use by covering the paintwork with a few coats of polyurethane or exterior varnish. Polyurethane and Varnish are waterproof finishers that can be used to seal bare wood and painted wood for outdoor use.

If you don’t want to use a sealant, you can cover the painted wood with a wood sealer. However, if you are on a budget, you can go for waterproof paint like exterior latex paint instead of buying the paint and a sealant.

This post reveals all you need to know about sealing a painted wood including the tools needed to carry out the task. Let’s dive in.

What Are The Benefits of Sealing Wood?

The benefit of sealing painted wood is to protect the wood against all types of water and wood damage. When wood is used outdoors, the wood will be exposed to all sorts of harsh conditions that it isn’t exposed to indoors.

Nothing damages wood faster than water and when the wood is used outside, it will be exposed to high humidity levels and rainfall.

If the wood is left exposed and without a sealant, it will become waterlogged and will eventually rot. However, if there is a sealant on the wood, the sealant will protect against water damage.

Here are other benefits of sealing painted wood:

1. To Preserve the Finish

When wood is painted, the paint dries to form a finish on the wood surface. It can be a matte, eggshell, semi-gloss, or high-gloss finish depending on the type of paint used. The finish can also be a certain color or have no color at all.

Some oil-based paints give tones rather than colors and you can get honey or gold tones on the wood. Regardless of the type of finish that you get, the finish will not last long if you don’t seal it.

However, when the finish is sealed, the sealant will protect it from moisture, dents, scratches, and stains making the finish last longer on the wood. You can even retouch the sealant when it gets old while the finish underneath remains protected.

2. To Prevent Mold Growth

Sealing wood also prevents mold growth on the wood. When wood is exposed to moisture, contaminants, and air, the wood will develop mold sooner or later because all of the requirements needed for mold on the wood are present.

However, when the wood is sealed, it becomes impossible for mold or fungi to grow on it. Some sealants even have mold-killing additives to stop and prevent mold growth.

3. To Protect Against UV Rays

Sealing wood also protects the wood from UV rays but this is only when the sealant is reinforced with UV blockers.

Not all sealants have UV blockers but if you need one with UV blocking additives, you should go for sealants designed for outdoor wood like exterior polyurethane varnish.

Without this type of sealant in place, your wood will gradually deteriorate and wear down when exposed to UV rays from the sun.

4. To Protect Wood From Pests

Sealing your wood also repels insects like termites and other bugs from making a home in the wood. This is especially important for wood structures made to support weight like front decks.

These structures can give way if infested with termites so a sealant is put in place to deter the insects and protect the frame of the wood structure.

5. To Give a Glossy Finish

Paints especially the water-based types hardly have any sheen and when applied on wood, all you get is a colorful but dull finish.

So, to improve the luster of the paint and make it shine, painters often apply high-gloss sealants on the painted wood. When dry, these sealants will reveal a transparent but glossy finish that will bring your paintwork to life.

When You Should Not Seal Painted Wood?

Usually, sealing painted wood is a great idea but, in some cases, it’s a terrible idea. Here are some of such cases:

1. When the Paint Has an Existing Sealant

Usually, after painting woodwork, the painter will seal the woodwork with a sealant. If there is an existing sealant on the painted wood, do not seal it. In this case, you can only seal the painted wood after stripping or sanding off the existing sealant.

To know if there is an existing sealant/sealer on the painted wood, use the water test. To do this, sprinkle some water directly on the painted surface and wait a few minutes. If the water is absorbed into the wood, then there is no sealant on the wood.

If you notice that the water starts to dissolve the color of the wood, it also means there is no sealant on the wood and you can apply a new sealant.

However, if the water has no effect on the wood and just remains on it, then there is an existing sealer on it that needs to be removed before another sealer is applied.

2. When a Waterproof Paint Was Used

Using waterproof paint on the wood will also result in the same case as having a sealer on the wood. In both cases, the sealer or waterproof paint will not allow the new sealant to stick.

So, if there is waterproof paint on the wood, don’t seal it unless the waterproof paint is stripped off of the wood first using a chemical-based paint stripper.

3. When the Paint Was Used for Its Unique Finish

If the paint was used to reveal a unique finish on the wood, do not seal it or you’ll ruin that particular finish. This is because when a sealant is used, you usually end up with a glossy and reflective finish.

For instance, if chalk paint was used on the wood for its unique antique finish, sealing the wood will no longer give you an antique finish. Instead, you’ll get a glossy finish because the sealant will cover the antique finish of the chalk paint.

What to Use To Seal Painted Wood in the Outdoors?

What to Use To Seal Painted Wood in the Outdoors?

When it comes to sealing painted wood, some products and methods stand out over others. Here are the top 3 methods that you can use to seal painted wood:

1. Use Exterior Sealers

The best way to seal painted wood to be used outdoors is to use an exterior sealer. Exterior sealers are thick and ultra-durable coats that protect outdoor wood from moisture damage, UV rays, dents, scratches, and UV rays.

The durability of exterior sealants is caused by the presence of chemical and solvent-based additives in their formula. Some sealants also have a good percentage of plasticizers and urethane compounds in their formula making it possible for the finish to stretch and contract based on temperature changes.

Here are amazing options to choose from:

  1. Exterior polyurethane
  2. Lacquer (on water-based paints)
  3. Exterior Varnish
  4. Spar Urethane

1. Use a Water Sealer

You can also use water sealers like Thompson water sealer to seal the painted wood but you need to ensure that the paint is completely dry before applying the water sealer.

Water sealers have different formulas depending on the type and brand of water sealer but one common feature of all water sealers is that they are waterproof when dry and can be used over painted wood. As an expert tip, always pick a water sealer that is compatible with the type of paint on the surface.

3. Apply Wood or Furniture Wax

The third method to seal a painted wood surface is to apply wax. Wax is a jelly-like coat that repels moisture when dry and can be used over painted wood.

You should ensure to purchase waterproof wax because these products often differ based on the brand and type of wood wax. The Howard Sunshield outdoor furniture wax is a good choice.

Next, let’s find out how to seal painted wood for outdoor use.

How To Seal Painted Wood For Outdoor Use?

When it comes to sealing painted woodwork, DIYers often question the dry time, the number of coats to apply, how long before applying the next coat, and so much more.

Luckily, this guide reveals how to seal painted wood in 4 steps. But first, we need to gather a few tools and supplies:

  • Fine-grit sandpaper
  • Wood filler
  • The required sealer (for this guide, we’ll be using polyurethane)
  • Clean rags
  • Paintbrushes
  • A pair of gloves
  • Mineral spirits
  • Some paint

Here is a 5-step guide to sealing painted wood:

1. Wipe and Clean The Painted Wood

Wipe and Clean The Painted Wood

The first step is to wipe and clean the painted wood. Use a clean rag for this and ensure the rag is dry. If you use a wet rag or filthy rag on the painted wood, the rag will ruin and smear the paint. The purpose of cleaning the rag is to remove dust and stains on it so the sealer can adhere properly.

When the wood is clean, inspect it for dents and damages. If there are discolored or scratched parts on the painted wood, you should touch up those areas with a fresh coat of paint. Allow the paint to dry before moving on with the task.

2. Scuff The Wood With Fine Sandpaper

Scuff The Wood With Fine Sandpaper

The next step is to scuff the painted wood with a fine-grit sandpaper. Usually, 320-400 grit is good enough.

The purpose of scuffing the painted wood is to create tiny ridges on the paint that the sealer can adhere to. Sanding also helps to remove stubborn stains on the painted wood. After sanding the wood, vacuum the dust.

3. Apply The Sealer

Apply The Sealer

The next step on our list is to apply the sealer. To do this, follow the manufacturer’s instructions for whatever sealer you buy.

If you are using polyurethane, it’s very easy to apply it on painted wood and you can either use a roller, paint sprayer, or a paintbrush. You should apply thin coats of the polyurethane and wait 4 hours between coats of water-based polyurethane and 10 hours between coats of oil-based polyurethane.

You don’t have to sand between coats of polyurethane but a light scuff with 400-grit sandpaper will increase your chances of a perfect finish. You need 3 coats of polyurethane on the painted wood for good coverage and durability.

4. Leave The Sealer To Dry

Leave The Sealer To Dry

After applying the sealer, leave it to dry for at least 3 days before normal use is resumed. Some sealers especially oil-based types can take up to a week to cure before normal usage can be resumed.

How Often Should You Seal Wood For Outdoor Use?

You should seal outdoor wood every 5-10 years for outdoor use. It’s difficult to state when exactly you need to seal the wood for outdoor use because the frequency is determined by the type of sealer on the wood.

Exterior polyurethane for instance can last up to 10 years if applied correctly while exterior wax doesn’t last that long.

So, if you seal your outdoor table with exterior polyurethane and seal the outdoor chair with wax, you’ll need to reseal the chair for outdoor use sooner than you’ll have to seal the table.

Can You Seal Any Type Of Wood?

You can seal any type of wood because wood generally accepts sealers. However, the type of sealer to use on the wood is another question. Penetrating sealers like oils generally don’t work well on softwood like Pine because softwood doesn’t absorb oils evenly.

Instead of penetrating sealers, you can use polyurethane on softwood because polyurethane doesn’t penetrate the wood.

On the other hand, hardwood like Oak accepts all types of sealers. The bottom line is you can seal any type of wood but the type of sealer required varies from wood to wood.

Final Words

In summary, you can seal painted wood and you have a wide range of sealers and top coats to pick from. You can go with traditional sealers like polyurethane or water sealers like the Thompson water seal.

You can also use exterior wood wax or apply waterproof paint on the wood. It all depends on your choice and the type of wood you are working on.

Always remember to properly prep the painted wood before application and don’t use coarse sandpaper to sand painted wood as that will remove the paint.

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