If you’re thinking about waterproofing painted wood, it’s probably because the wood is outdoors, or in a bathroom or similarly damp interior environment.

In these situations, Tim Conn, president and co-founder of commercial cleaning solutions company Image One USA, advises three strategies: spraying a sealant, applying a waterproofing top coat, or mixing a waterproofing additive with your paint.

Wood tends to swell and contract with changing humidity. That does a number on paint finishes that aren’t supposed to be outdoors.

“Without proper waterproofing, your painted wood can be susceptible to damage from water and moisture, resulting in cracks, warping and discoloration,” Conn says. Even worse, paint that isn’t waterproofed can fade and actually flake off.

This can be a real problem when you’re painting signs for outdoors. You’ve probably seen at least one nearly illegible wooden sign whose message has been lost to the elements. That won’t happen if you properly waterproof the paint.

Does Painted Wood Need Waterproofing?

Yes and no.

If you painted with an exterior latex or oil-based formulation, then no. Exterior paints are made to withstand outdoor conditions. They’re flexible, resist cracking when wood swells and contracts, and repel moisture. Most also control the growth of mold and mildew. If you need to re-coat wood with exterior paint, another coat of the same type is all you need.

Interior paint formulations aren’t as robust. So if you choose an interior enamel or wall paint for its color or some other reason, you’ll need to waterproof it. The same goes for chalk, clay and milk paint.

What’s the Best Moisture Damage Protection on Wood?

The best waterproofing sealant maintains the original appearance of the paint as much as possible, while protecting it from the weather. Conn recommends three options that perform these tasks to varying degrees of efficacy.

Spraying a sealant

“Sealants are a popular choice for waterproofing painted wood because they provide a protective barrier without altering the appearance of the paint,” says Conn. “They create a waterproof layer on top of the paint while still allowing it to breathe.”

However, sealants typically contain silicone, which repels new paint as effectively as it does water. Silicone can be difficult to remove if you choose to repaint your wood.

Applying a waterproof top coat

You can waterproof most types of paint by coating them with clear polyurethane or acrylic. This method can be as effective as spraying a sealant, but may change the paint’s appearance by adding a glossy or shiny finish.

In some cases, a waterproofing top coat may also add an amber hue, but that isn’t necessarily a bad thing. Even a small amount of pigmentation blocks UV sunlight and protects the finish.

Using waterproof paint

If you’re dead set on using an interior paint outdoors, you can mix in a waterproofing additive like Paint Proofer to help it repel water and resist mold and mildew. You can also choose a paint with a waterproofing agent already mixed in.

But Conn says these paints “may not be as durable as other waterproofing methods and may require more frequent touch-ups.”

How To Waterproof Painted Wood

If you need to waterproof painted wood, you have two options: sealing and top-coating. Conn recommends keeping the following tips in mind:

1. Clean and prepare the surface: Before applying any waterproofing product, make sure the painted wood is clean and free of dust and debris. Sand any rough spots or imperfections to ensure a smooth surface.
2. Test the product first: It’s always a good idea to apply it on a small, inconspicuous area of the painted wood first. This will help you determine if the product alters the appearance of the paint or causes any issues.
3. Follow instructions: Always adhere to the manufacturer’s instructions for proper application. This may include using specific tools or techniques, and allowing enough drying time between coats.
4. Apply more than one coat: Depending on the product, you may need multiple coats for maximum waterproofing protection. Be sure to allow each coat to dry fully before applying the next one.

Waterproofed Painted Wood Maintenance

Waterproofing finishes can deteriorate rapidly in harsh outdoor conditions, especially if the wood faces direct sun. Conn recommends regularly checking for any signs of damage or wear, and touching up as needed to ensure continued protection.