How to Waterproof Wood for Bathroom? (3 Methods)

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

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

Pros Of Using Waterproof Wood In Bathroom

Pros Of Using Waterproof Wood In Bathroom

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

Waterproofing the wood protects it from all types of water damage. Here are other advantages of using waterproof wood in the bathroom:

  1. Beautifying Wood – Using wood oils to waterproof bathroom wood 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 wood.
  2. Durability – Bathrooms are high-moisture areas, and the constant exposure to water will ruin the bathroom furniture fast. So, waterproofing bathroom wood will increase its durability and protect it from water. 

Types of Wood You Can Waterproof For Bathrooms

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

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

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

Here are the top 5 types of wood that you can waterproof and use for bathrooms:

  1. Pine Wood

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

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

  1. Koa Wood

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

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

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

  1. Oakwood

You can waterproof oak wood for bathroom use. The wood is easy to paint, stain, and seal.

There are two types of Oakwood; red and white Oak. Red oak is more water prone than white Oak, so White Oak is a better option for bathroom wood. 

However, you still must apply a water-resistant sealer over white oak wood. 

  1. Plywood

You can use plywood as bathroom wood, but you must seal it. To seal plywood, use polyurethane or varnish. You shouldn’t use wood oils over plywood without a wood conditioner or sanding sealer. 

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

  1. Teak Wood

Teak wood is water-resistant, durable, and strong. To use Teak wood in the bathroom, seal it with polyurethane or varnish.

Prepping The Bathroom Wood For Waterproofing

Here is how to prep your bathroom wood for waterproofing:

1. Clean The Wood

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

To clean wood, use TSP or soapy water. 

2. Remove Existing Sealer or Finish

If the bathroom wood is already sealed, you must remove it before applying a new one. That’s because the existing top coat won’t allow the new sealer to stick. Instead of removing the sealer, you can also abrade it. 

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

To remove an existing sealer:

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

3. Repair The Bathroom Wood

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

How To Waterproof Wood For Bathroom?

You can waterproof wood for bathroom by using:

  1. Sealer (Thompson water seal)
  2. Wood oils (Tung oil)
  3. Varnish (Polyurethane)

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 interior wood surfaces, including bathroom wood. This water sealer penetrates the wood grain and seals the wood pores from the inside. This prevents wood from absorbing water.

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

Here’s how to use it:

  1. Clean The Wood – Remove the dust and filth from the wooden surface. 
  2. Apply the Thompson’s Water Sealer – Once the wood is clean, apply the water sealer. To apply Thompson’s water sealer, use a paintbrush, roller, or sprayer. For a horizontal wood surface, pour the Thompson’s water sealer directly on the wood 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 wood finishes that can waterproof wood. The best wood oil to waterproof bathroom wood is Tung oil. Tung oil is a natural wood oil gotten from the Chinese Tung tree.

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

Here is how to waterproof wood using Tung oil:

  1. Prep (clean) the bathroom wood. 
  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. Leave the wood oil 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 Tung oil only becomes fully waterproof when the oil 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)

The best way to waterproof a bathroom wood is to apply varnish (or 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 wood grain, creating the perfect wood for your bathroom.

Here’s how to use it:

  1. Prep the wood.
  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.

The lifespan of Waterproof Wood in Bathrooms

A waterproof wood lasts 10-20 years in the bathroom. However, the lifespan of a waterproof bathroom wood 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 a bathroom wood sealed with tung oil. 

Under peak conditions, waterproof wood must last up to 20 years in bathrooms. 

Final Words

You can use wood in bathrooms, but you must waterproof the wood. To waterproof bathroom wood, use polyurethane, Thompson’s water sealer, or tung oil.

Allow the sealer to dry and cure over the wood before using the wood in bathrooms. 

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