How to Waterproof Wood for Outdoor, Bathroom, and Other Use

How to Waterproof Wood for Outdoor, Bathroom, and Other Use

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When it comes to constructing an indoor or outdoor project, you have a variety of materials to choose from. Some materials are extra sturdy while others provide an unbeatable aesthetic style. Wood provides both of those traits and more, making it a go-to option for many builders.

However, depending on how you incorporate wood into your project, it may become susceptible to one of its greatest enemies, water. Because of wood’s basic structure, wood planks, panels, and boards are at risk for damage when they are exposed to wood. Damage of this sort occurs when water is absorbed into the wood, causing it to swell up in turn, or when an abundance of moisture causes the wood to rot, resulting in more rapid decay.

While this is a clear weakness, waterproofing wood holds the potential to avoid all of these problems while preserving wood’s essential beauty and strength.

There are several ways to waterproof wood today. This guide will take you through those methods while teaching you which method is the best one for use in a bathroom or outdoors. This guide will also make it clear why waterproofing is an absolutely essential wood preparation step that no DIYer should ever skip over.

Why Waterproof Wood?

You may be wondering, “why should I spend the time and money to waterproof my wood?”

The answer here is simple. If you want your wood to last longer, look better, and remain as sturdy as possible, then you need to waterproof it. Water and even light moisture can degrade a piece of wood’s structure, causing it to become weak and moldy as a result.

Waterproofing prevents this undesirable end result by preventing moisture from piercing a piece of wood’s porous exterior.

Why Waterproof Wood

How to Waterproof Wood: A Step-by-Step Guide

Now, let’s take a look at the three most common methods of waterproofing wood starting with the most traditional one.

Method #1: Hand-Rubbed Oil

This first method is very traditional and involves the application of a mix of linseed and tung oil. This gives the wood a rich, dark color while also creating a waterproof layer over its surface. This method is best suited to wood pieces that will be regularly exposed to moisture but will not regularly be put under pressure from friction.

Step 1: Buy or Mix Oil

First, you’ll need to buy some pre-mixed oil or create your own mixture. To do the latter, procure linseed oil and Tung oil, as well as a vented container to mix them in.

Combine one part of each oil type with one part mineral spirit and one part liquid polyurethane. Stir this mixture thoroughly and test it out on a scrap piece of wood. Add more of either type of oil if you want the resulting finish to be darker.

Step 2: Apply the Mixture

After procuring your oil mixture, begin to apply it to your wood’s surface with a natural-bristle brush. Apply even pressure as you do this and always apply the brush strokes in the same direction. Continue to do this until the entire surface is covered.

After allowing the oil to sit for an hour or so, pick up some clean rags and begin to “rub” the residual oil into the wood’s surface. Do this with even pressure until all residual oil is removed from the wood’s surface. After this is complete, allow the waterproofing finish to dry for up to 24 hours.

Step 3: Sand and Reapply

Once your finish has entirely dried (I wrote more about tung oil drying time here), you may choose to lightly sand it with fine-grain sandpaper. This prevents the surface from becoming too slick, which can be dangerous in adverse weather. Then, you may choose to add additional coats of waterproof finish until the desired result is reached.

Method #2: Sealant

Artificial sealants are perhaps the most popular waterproofing option, not the least because they are very reliable.

In most cases, sealants are made up of polyurethane, varnish, and lacquer, allowing them to resist water effectively while providing rich color to the wood beneath. They also tend to dry with considerable ease and only need to be reapplied occasionally.

As such, they are a solid option for both indoor and outdoor use.

Step-by-Step Guide

In most cases, sealant can be purchased in its pre-mixed form from a local hardware supply store. There are a variety of styles on the market today, each of which come with varying strengths and prices. You can also find differing mediums for applying sealant today, making it difficult to describe just a single method.

However, most sealants come in a can or bottle, similar to paint. Also, much like paint, they can be applied to a dry and clean wood surface with a regular paintbrush. From there, the sealant can dry over a number of hours, after which additional coats may be applied.

This cycle can be repeated as many times as that particular mixture recommends for reaching the desired color and level of protection.

Also, you may be able to find a spray-on sealant that suits your needs.

These mixtures tend to be easy to apply via a built-in spray nozzle. Using these sprayers can differ from one brand to another, so always check your chosen brand’s application method before starting the process.

Method #3: Stain-Seal Combo

Stain-seal combos look and act a lot like standard sealants on the surface.

However, their most notable differences include a larger range of pigment color options and a far faster drying time. As a result, stain-seal combos are ideal for waterproofing if you are looking for a precise finish color or are short on time.

Step-by-Step Guide

A stain-seal combo usually comes in a liquid form and can be applied to dry, clean wood per the package’s instructions. Usually, this can be done with a standard paintbrush. However, no wiping is necessary to remove excess liquid.

This is because stain-seal combo soaks into the wood upon which it is applied. This also has the added effect of causing a stain-seal combo to dry rapidly.

HW Recommends

Ready Seal 112 Natural Cedar Stain and Sealer for Wood

Requires no primer before applying. Can be used with a sprayer, roller, or brush.

Waterproofing Wood for Outdoor Use: Tips & Tricks

While waterproofing your outdoor wood is essential for protecting it long-term, it also helps to choose the right wood for your region in the first place. That’s because certain wood types are better suited to withstand the elements of that region, even before a waterproof coating is added.

As such, a regionally-compatible wood choice can help an outdoor deck or wood table last through many decades of outdoor exposure as long as it’s regularly sanded and stained.

Generally speaking, most outdoor carpenters agree that redwood is a solid choice for homeowners on the US West Coast. This is because the wood is both abundant and resilient to the year-round sun and mild temperatures. Meanwhile, red cedar is usually the go-to pick in the Midwest for its ability to withstand cold weather and ice during the winter. Finally, homeowners in the eastern US will find Cyprus wood to be the best for dealing with the region’s wet winters.

Waterproofing Wood for Outdoors

Waterproofing Wood for Bathroom Use: Tips & Tricks

If you plan on waterproofing any wood in your bathroom, consider the following before starting the task.

First and foremost, only apply the sealant to wood that is fully dry. This can often be hard to judge, especially if you are waterproofing a piece of wood that was already in the bathroom. To ensure the best results, remove the wood from the bathroom space and allow it to dry under a warm light for at least a day before applying the sealant.

Also, when the time comes to apply your waterproofing agent, be sure that you are working in a room-temperature environment. Hot and cold environments can cause sealants to behave in different ways, which in turn causes them to dry and settle unevenly.

In particular, hot and enclosed environments should be entirely avoided due to the risk of inhalation of sealant fumes. If possible, always complete any coating jobs outside, rather than in the bathroom proper.


Waterproofing your outdoor or indoor fixtures need not be a difficult task. Even so, it is absolutely essential that you utilize one of the three methods described above. Otherwise, your wood’s exposed surface may take on moisture that causes it to degrade or rot in the short term.

You most certainly want to avoid these results, so be sure to make plans to waterproof your wood fixtures before calling your next woodworking job complete.