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Waterproof Wood

How To Waterproof Wood For Your Bathroom

When it comes to home improvements, many people love the idea of having a nicer bathroom. There are many ways in which you can improve a bathroom, but all of them must deal with the problem of moisture. Due to the frequent use of hot water, these rooms are often filled with steam and water vapor. That can be a serious problem if any part of your bathroom is furnished with wood.

Thankfully, there are multiple ways in which you can address this problem. Wood can be waterproofed in several ways, allowing you to add a touch of natural beauty to your bathroom. Let’s go over the four most common ways of achieving this.

Waterproofing With Oils

This is the oldest and simplest method of waterproofing, and it might also be the easiest. By rubbing an oily substance into the grain of the wood, you create a water-resistant top layer. This happens because the oil is absorbed into the wood, where it stays for a very long time.

Of course, not all oils can be used to treat wood. Even common vegetable oil can be used to treat wood, but it will not provide a truly waterproof surface. To fully protect the wood, you need something made from linseed oil or tung oil. One of these solutions (the linseed oil) is of European origin, while tung oil is the Chinese equivalent. Modern versions are often mixed with other ingredients to make them dry faster and stronger.

The chemical properties of linseed oil and tung oil are actually very similar. Both of them contain mixtures of linoleic acid, stearic acid, oleic acid, and palmitic acid. These two substances are basically just different mixtures of the same ingredients. Unlike most oils, these will leave behind a hard and water-resistant layer. If you want a good example of this kind of finish, the clear coating of a guitar (traditionally done with linseed oil) would be one.

To use oils for waterproofing wood, follow these steps:

  • 1. Prepare the wood surface with a little bit of sanding and cleaning.
  • 2. Stir the oil vigorously for as long as the label demands.
  • 3. Using a natural-bristle paintbrush, apply the oil liberally to all parts of the surface. Try to spread the oil as evenly as possible.
  • 4. Wait until the oil has soaked into the surface, and then give it a touch-up job. Re-apply the oils to any area that looks dry.
  • 5. When the oil has once again soaked into the surface, use a clean, dry cloth to wipe away the excess.
  • 6. Leave the wood surface to dry for 12-24 hours. Some products will allow you a shorter wait time, but a full day is always the safest bet.
  • 7. Using super-fine sandpaper or steel wool, give the surface a light sanding to remove any unsightly globs.
  • 8. Wait 24 hours, then repeat steps 1-6 if additional coats are desired.

Waterproofing With A Sealant

Now let’s look at the more modern option. Wood sealers are distinct from oils in the fact that they create a watertight seal between the surface of the wood and everything from the outside world. The most common type of sealants (by far) are those made from polyurethane. However, you can also opt for lacquer or varnish.

Lacquer is basically just a resin that is derived from a tree. This resin (usually pine resin) is suspended in alcohol, which evaporates easily, leaving a moisture-proof covering. Varnishes, on the other hand, contain tree resin, various solvents, and some drying oil. These are good options, but polyurethane tends to be both cheaper and longer-lasting.

Polyurethane sealers can be water-based or oil-based, and both of these types have their distinctive strengths and weaknesses. Water-based sealers are definitely the most popular, and that is because they are more pleasant to use. They don’t have the harsh chemical smells that oil-based sealers will often have, and can easily be cleaned up with soap and water. As such, polyurethane sealers are much more forgiving of mistakes.

Of course, there are a few little things which you need to be careful to avoid. Cheaper, low-quality polyurethane products have a tendency to turn yellow over time. None of them will advertise this quality, but one look at the review section for a cheaper product will tell the tale. The last thing you want is for your bathroom to have a sickly yellow hue. When people walk in, you want them to feel that they are in a clean environment.

You also need to make sure you don’t shake the sealant, as this will cause air bubbles to develop. You can gently stir the sealant if you want to, but that isn’t necessary unless the product has sat idle for a long time. Finally, you want to make sure that you use the sealer at room temperature. Excessive heat or cold can affect its ability to cure properly, making it useless.

To waterproof wood with a sealant, follow these steps:

  • 1. Prepare the wood surface by sanding and cleaning. A pressure washer is also an option.
  • 2. Use fans and open windows to achieve good ventilation in the work area.
  • 3. Using a soft brush, apply the sealer to the entire surface. Use long, even strokes so as not to leave streaks or globs behind.
  • 4. Check the instructions to see how soon the surface can be re-coated. When the time has elapsed, apply up to five coats.
  • 5. Using fine sandpaper or a razor blade, go over the surface and remove any bumps or globs that may have been left behind. Do this carefully until you get a perfectly smooth surface.
  • 6. Use a polishing or rubbing compound to remove the marks you made when smoothing the surface.

Waterproofing With A Stain/Sealer Combo

As you have already seen, most sealers are either oil-based or polyurethane-based. However, there are also blended products that attempt to give you the best of both worlds. One of these combination products is a stain/sealer combo. When you are planning to stain and seal your deck, for instance, this kind of product can save you time by turning two steps into one.

These products combine a polyurethane sealer with pigment, but the proportions can make a big difference. For instance, if the product contains very little pigment, it will only offer a change of shade rather than a color change. It will just give the wood a colored tint, while one with more pigment would actually change its color. If you want to customize your results, you can mix it yourself.

These products can be water-based, oil-based, or alkyd-based. Although all of these products will do the same thing, there are small differences between them. Water-based products are less volatile, easier to clean up, and form a harder surface. Oil-based products will take longer to dry but will add a lot to the beauty of the wood. Oil-based versions will also soak into the wood more deeply, giving a deeper and longer-lasting finish.

Alkyd-based products, on the other hand, are distinct in the fact that they leave a surface layer rather than penetrating the wood. In general, it is recommended that you do not use alkyd-based products for outdoor projects. Over time, they have a tendency to peel away, while a penetrating sealer does not. For a bathroom job, you probably don’t need to worry too much about that, and so an alkyd-based product wouldn’t be a bad choice.

Chances are, your main reason for using wood in the bathroom is its beauty. If you were only interested in practical reasons, you would probably go with plastic, ceramics, and stone in your bathroom (all of these substances are much more waterproof than wood, obviously). For this reason, a combination of stain and sealer is likely to produce the best results for a project of this type.

To use a product of this type, simply look at the instructions on the label and follow them to the letter. We cannot give you a universal set of instructions for these blended products because there is a lot of variation from one to another. Thus, the best thing to do is to follow the manufacturer’s instructions.

Waterproofing With An Oil/Varnish Mixture

When it’s time to choose between an oil and a sealer, you might be asking yourself, “why not both?” If you really want to get the benefits of both types, you can and should opt for an oil-varnish mixture. To save money, most people prefer to mix these products themselves.

The best thing about the DIY approach is the opportunity for customization. By tweaking your recipe a little bit, you can change the properties of each mixture to fit whatever project is being done. The standard recipe is equal parts boiled linseed oil, paint thinner, and varnish. The linseed oil can be substituted with tung oil, and you can use pretty much any sort of paint thinner. Mineral spirits are probably the most popular choice, but you can experiment with others. As for the varnish, this can be polyurethane, resin-based varnish, or anything similar.

By controlling the amount of linseed/tung oil in the mixture, you can control its penetration, drying time, and appearance. Mixtures with more oil will tend to darken the wood, penetrate deeper, and dry slower. By controlling the amount of paint thinner in the mixture, you can control the thickness and potency of the product.

If the mixture is too thick to be easily spread, you need more thinner. Finally, you can control the degree of moisture protection in the final product by adjusting the amount of varnish. You can also change the properties by using resin-based finishes like lacquer, although this is not the common way to do things. Although it takes some trial and error, this method will help you to produce the best custom-made waterproofing mixture that you can.


Over the years, people have invented a wide variety of ways to waterproof wood. As for which of these is the best, it will depend on the project. For instance, a sealer would probably be the best choice for something that is sure to get wet. For instance, an outdoor log bench will benefit from the superior moisture protection of a pure poly sealer.

On the other hand, you would probably not choose a pure poly product for your bathroom since you want to increase the beauty of the wood. That’s why we would recommend the stain/sealer combo for most instances. At the same time, we hope that you will do your research, experiment a little bit, and find the method that works best for you.

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