How to Waterproof Wood for Bathroom? (3 Methods)

You must waterproof wood in the bathroom to prevent it from swelling and rotting. So, how to waterproof wood for bathroom use?

To waterproof wood for the bathroom, use a sealer. When dry, the sealer will form a thick glossy layer that protects the surface from moisture, water, and scratches. You can also waterproof it by covering it with a carpet.

Common sealers to use on bathroom wood are polyurethane, varnish, and Thompson water sealer. The sealer must be waterproof, or at least water-resistant, to protect it.

Should You Do it?

Pros Of Using Waterproof Wood In Bathroom

The primary advantage of waterproof bathroom wood is that it protects it from water damage. Since wood is porous, it will absorb water, which causes it to swell and warp, resulting in uneven lines on the surface. If left unchecked, it will begin to rot. 

But, waterproofing protects it from all types of damage. Here are some other advantages: 

  1. Beautifying Wood – Using wood oils to waterproof it will beautify it. Wood oils, such as tung or linseed oil, will add a coat of sheen to your bathroom wood. This sheen is reflective and beautifies the surface.
  2. Durability – Bathrooms are high-moisture areas, and constant exposure to water will ruin the bathroom furniture fast. So, waterproofing them will increase their durability and protect them from water. 

Types of Wood To Waterproof:

When choosing a wood type to waterproof, you must consider a few things:

  • The waterproofing properties of the wood.
  • How well it accepts paint, wood stains, and most importantly, sealers.
  • Its durability

All three factors determine how well the wood will repel water and how long it will last in your bathroom.

  1. Pine Wood

Pine is an affordable softwood that works great for bathroom use. Since pine is a type of softwood, this means it’s non-porous and has good water-resistant features.

However, it isn’t waterproof, and you must apply a waterproof sealer to protect it. To seal it, use polyurethane or Thompson’s water sealer coating.

  1. Koa Wood

Koa is an ultra-durable hardwood that can be waterproofed for bathroom use. Its strength and durability is ideal for bathroom cabinets and other heavy-duty furniture.

Asides from its strength and durability, it also has a unique reddish appearance that can complement the décor of your bathroom.

Unfortunately, Koa wood is not water-resistant. Being a hardwood, it is porous and absorbs water easily. However, its porosity also means it accepts stains and sealers evenly. So, it will be easy to seal and waterproof.

  1. Oakwood

You can waterproof oak wood since it’s easy to paint, stain, and seal. There are two types of it; red and white Oak. Red oak is more water prone than white Oak, so White Oak is a better option for bathrooms. However, you still must apply a water-resistant sealer over it.

  1. Plywood

You can use plywood in your bathroom, but you must seal it. To seal plywood, use polyurethane or varnish. You shouldn’t use wood oils over it without a wood conditioner or sanding sealer. That’s because its surface is very porous and will absorb too much wood oil. 

Also, there are different grades of plywood in the market, and A-grade plywood is considered the most durable and water-resistant type of them all.

  1. Teak Wood

Teak wood is water-resistant, durable, and strong. However, you must seal it with polyurethane or varnish before using it in a high-moisture area. 

How To Prep The Wood?

Before waterproofing it, you must prep the wood and make it ready to accept the sealant coating. If you don’t, the finish will look amateurish and can peel off. 

1. Clean The Wood

The wood must be dry and clean before applying a sealant. If you don’t clean it, the sealant won’t stick properly because the dirt and grime will prevent good adhesion. Also, most sealers are clear coats, so the dirt and filth will show once the finish dries. 

To clean the wood, use TSP or soapy water. Avoid using too much water as the word can absorb it. It’s best to dampen a rag with TSP or soapy water and then wipe the dirt off. 

2. Remove Existing Sealer or Finish

If the wood is already sealed, you must remove the existing finish first. That’s because the existing sealant won’t allow the new sealant to stick. Instead of removing the sealer, you can also abrade it. 

To abrade an existing finish, use medium-grit sandpaper. This sandpaper will remove some “parts” of the existing sealer, so the new can penetrate into it. 

To remove an existing sealer:

  1. Use a chemical-based paint stripper and steel wool. 
  2. Once the finish is removed, sand the surface with fine-grit sandpaper.
  3. Remove the paint stripper residue. 

3. Repair It

If the wood is cracked, damaged, or has dents, you must repair it before waterproofing. To repair it, use wood filler. 

How To Waterproof Wood For Bathroom?

Waterproofing bathroom wood isn’t hard, but you must prep its surface properly and use the right type of sealant. 

Here are top 3 methods you can use:

1. Use Thompson’s Water Seal

Use Thompson's Water Seal

Thompson’s water seal is a silicone-based transparent seal that can be used on outdoor and indoor surfaces. This water sealer penetrates the wood grain and seals the pores from the inside. This prevents the surface from absorbing water.

Also, the transparent finish of Thompson’s water sealer highlights and preserves the natural beauty of the wood. 

Here’s how to use it:

  1. Clean The Surface– Remove the dust and filth from the surface. 
  2. Apply the Water Sealer – Once the surface is clean, apply the water sealer. To apply Thompson’s water sealer, use a paintbrush, roller, or sprayer. For a horizontal wood surface, pour it directly on the surface and allow it to settle. For vertical surfaces, start at the bottom and work your way up. 
  3. Apply Another Coat – You must let the first coat of the water sealer dry for 90 minutes before applying the next coat. 
  4. Let the Sealer To Dry – Allow the Thompson’s water sealer to dry for 48 hours. 

2. Use Wood Oil (Tung Oil)

Use Wood Oil (Tung Oil)

Wood oils are natural finishes that can waterproof wood. It’s recommended to use Tung oil for this. Tung oil is a natural wood oil gotten from the Chinese Tung tree.

When applied, Tung oil penetrates the pores and seals the surface. It also dries to reveal a honey tone that matches the appearance of your wood. Asides from Tung oil, you can also use boiled linseed oil.

Here is how to do it:

  1. Prep (clean) the surface. 
  2. Thin the Tung oil with mineral spirits (only a small amount of mineral spirits is needed).
  3. Apply the first coat of Tung oil using a clean rag, bristled paintbrush, or foam brush.
  4. Allow it to dry for 24 hours.
  5. Sand the first coat with ultra-fine sandpaper and remove dust.
  6. Apply the second coat and leave it to dry for 48 hours.
  7. If needed, you can buff the finish using a polishing cloth.

Tip: When the Tung oil is dry, you shouldn’t subject it to high humidity yet because it only becomes fully waterproof when it has cured, and this can take up to a week. Pure tung oil can take up to 21 days to cure.

3. Use Varnish (Polyurethane)

Use Varnish (Polyurethane)

Polyurethane is a hybrid varnish type containing solvents, urethane compounds, and resinous materials. The combination of these compounds produces an ultrathick and water-resistant film known as polyurethane.

There are two types of polyurethane; oil-based and water-based polyurethane. Both types of polyurethane work great to repel moisture, and the finish highlight the grain, creating the perfect finish.

Here’s how to use it:

  1. Prep the surface.
  2. Apply the first coat of polyurethane using a paintbrush or spray gun. You can also purchase ready-to-spray polyurethane cans.
  3. Leave the first coat of polyurethane to dry for about 8-24 hours before recoating. It’s important the first coat dries well before the second coat.
  4. Apply the second coat and leave the surface to dry for 24 hours.

Durability

A waterproof wood lasts 10-20 years in the bathroom. However, how long it will last depends on the maintenance routine, the quality of the wood, and the type of sealer used.

For example, a bathroom wood sealed with polyurethane lasts longer than one sealed with Tung oil. That’s because polyurethane is a stronger sealant and is more water-resistant than Tung oil. This means it protects the surface better and helps them last longer even if exposed to water. 

Final Words

You can use wood in bathrooms, but you must waterproof them. To waterproof bathroom wood, use polyurethane, Thompson’s water sealer, Tung oil, or any other waterproof or water-resistant sealant.

Allow the final coating of the sealant to fully dry (cure) before exposing the surface to water. 

Tony Adams
Tony Adams

Tony is a professional painter and an author of DIY Geeks. Tony has completed over 1,000 painting projects for his clients. It's safe to say he knows what he Is talking about,

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