How to Treat Wood for Outdoor Use

Wood is perhaps the most common building material on earth. Its only real competition in this regard is concrete, but wood has been used for far longer. Nevertheless, wood has always had one big problem: it rots and crumbles away.

Thankfully, human beings have come up with many innovative ways to prevent this decay. In this article, we will go over some of the methods used so that you can learn how to treat wood for outdoor use.

Wooden Patio
Wooden Patio. Photo:

How To Treat Wood For Outdoor Use

As I already mentioned, there are several different methods by which this can be done. We will go over the five most common of them. Any of these options may or may not be practical for you, but all of them should be understood before you make your decision.

Wood Sealers

Wood sealers are perhaps one of the surest ways to protect your wood from weathering and rotting. They work in a manner similar to that of the pressure treatment, but without the pressure. Wood sealers usually consist of some type of plastic/acrylic compound. This compound is then poured onto the wood and allowed to soak. When it dries, the top few inches of the wood have been encased in plastic, both inside and outside the surface.

Wood sealers are extremely easy to apply, and will only need to be re-applied every 1-5 years.
 If you go with this option, be aware that softer wood is more porous. As a result, it will require more sealer to give it adequate protection. On the plus side, softer wood will allow the sealer to soak in much deeper.

The process of using a wood sealer is very simple:

  • Step 1: Clean the surface of the wood and give it a light sanding.
  • Step 2: Apply the sealer to the surface generously. You can use a brush or dab it on with a cloth. A spray gun can also be used. It is very important that you don’t leave any visible streaks in the sealer.
  • Step 3: Allow the sealant to dry completely. Consult the product label for a good idea of how long that will take. 24 hours is typical, but some will be much quicker.
  • Step 4: Lightly sand the surface again before applying another layer of sealant. Make sure to use the finest grade of sandpaper you can find.
  • Step 5: Allow the second layer to dry, then do a third or fourth layer if desired.

Oil Finishes

Oiling Wood
Oiling Wood. Photo:

You might be wondering how people would waterproof their wood before plastic-based sealers came along. The answer is that they would treat outdoor wood with various types of oil finishes. It isn’t that hard to give your wood one of these hand-rubbed oil finishes, and they have the bonus of making the wood look really nice.

Most oil finishes made for wood are made from one of two things: Linseed oil or Tung oil. Linseed comes from a plant called Flax, while Tung oil comes from the Tung tree. Both of these plants offer similar properties, although they aren’t necessarily the same.

I would particularly recommend this kind of finish for dark woods like walnut, as the high level of shine will really add a lot to their appearance.

These oils soak into the grain of the wood, though they won’t soak as deeply as some other materials. Still, they will provide a waterproof surface, and that is the goal. Linseed oil has commonly been used for musical instruments and other expensive wooden crafts, while Tung oil has a history of use (in China, particularly) that goes back thousands of years. Some products will mix these two ingredients, and these are often sold under the trade name “Danish Oil.”

To apply a hand-rubbed oil wood finish, follow these steps:

  • Step 1: Clean the surface of the wood and give it a light sanding.
  • Step 2: Use a paintbrush with soft bristles to apply the oil finish to the surface.
  • Step 3: Allow the oil to soak into the surface entirely. Consult the product label for a better idea of your timeframe. If you see dry patches as the product dries, add a little bit more.
  • Step 4: Use some dry, clean rags to wipe off the excess oil that didn’t soak into the wood.
  • Step 5: Give the surface a light sanding.
  • Step 6: Apply as many additional layers as desired. Don’t forget to give the surface a light sanding between each layer.

Stain-Sealer Combinations

Wood Staining
Wood Staining. Photo:

If you are having trouble deciding between a stain and a sealer, you can easily do both at the same time. There are a number of different products that offer both stain and sealer in the same mixture. If you were going to do both of these things anyway, you could save time by doing all of it in one step.

These products are very simple in terms of their composition. By adding a dye to the polyurethane-based sealer, you get something that colors and seals at the same time. Light-colored wood can really benefit from this kind of finish. Polyurethane-based coatings will often yellow and fade over time, causing the wood to look older than its’ years. This effect is especially noticeable when using light-colored wood.

By using a stain/sealer combination, you can ensure that your wood is dark enough to hide any discoloration of the plastic finish that may occur. Not only that, but these products can provide a very precise ability to shade your wood. The amount of pigment added to the polyurethane will determine how dark of a finish you obtain.

To use a stain/sealer combination, just follow the same steps that you would use for a wood sealer product. Combo products are used in more or less the same way, although they will probably take longer to dry between coats. They may also require extra steps when preparing the surface, so make sure to read the label carefully and follow its’ directions.


Applying Varnish
Applying Varnish. Photo:

Varnishes are very similar to a sealer in the fact that they are normally made of polyurethane. However, many oil varnishes also exist, so what makes them unique? The thing that separates a varnish from an oil finish is the way in which it works.

Varnishes are not meant to soak into the wood, unlike most of our other options. Instead, a varnish creates a watertight coating, which is built up in successive layers to create a hard outside layer. This will function like a shell that keeps out unwanted moisture and absorbs impact without denting the wood itself.

To varnish anything made of wood, just follow these easy steps:

  • Step 1: Find a clean place in which to work. Dust, lint, and other small debris must not be allowed to contaminate the varnish. Your work area should also be well-ventilated.
  • Step 2: Use some fine sandpaper to give the surface a little more roughness. This will help the varnish to adhere. Make sure you sand with the grain of the wood for maximum smoothness.
  • Step 3: Use a tack cloth or something similar to remove all wood dust from the freshly sanded surface.
  • Step 4: Mix the varnish with mineral spirits (about equal parts). This will help it to cure harder.
  • Step 5: Lay your pieces flat, and apply the varnish with a soft-bristled brush. Start by brushing against the grain, then apply another layer brushing with the grain.
  • Step 6: Allow the varnish to dry completely. Consult product label for exact drying time (24 hours is typical).
  • Step 7: Add additional coats until the desired thickness has been reached.

Pressure Treatment

Pressure Treated Wood
Pressure Treated Wood. Photo:

This is an industrial process that is obviously not an option for DIY projects. By using a mix of hot water, pressure, and a variety of preserving agents, the wood is impregnated with preservatives. The pressure forces it deep into the grains of the wood so that it can prevent any chance of internal rotting.

The preservatives used are typically copper azole, alkaline copper quaternary, or some other copper compound. Because copper is incredibly resistant to weathering, it’s not too surprising that this ingredient would be used. If you buy pressure-treated lumber that looks wet, don’t worry: The water will evaporate, and the preservatives will be left behind.


There are other things that you can use to waterproof the surface of your wood. However, I have covered the five most common options and given you specific instructions as to their use. Most of the other methods are “niche” methods that most people won’t find to be practical.

I hope that this article has given you the knowledge to preserve your outdoor wood furnishings for as long as you desire. Don’t make the mistake of thinking that you don’t need to treat the wood, or you will soon see greying of the wood before it eventually rots away. Instead, use one of these methods to make it last for years to come.

William Stewart

The proud owner and lead writer of Started writing in 2018 and sharing his love and passion for wood treatments and crafts.

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Valerie Butcher
Valerie Butcher
1 year ago

Hello, I have a beautiful weepingwillow tree stump that I am wanting to preserve. Should I use the oil process or the plastic / acrylic process? I’m already starting to get fungus on it and I knew it won’t last very long if I don’t do something with it.

jim Claxton
jim Claxton
3 years ago

I have 15 year old cedar siding home org stain with flood clear acrylic stain the stain gain in seven years with flood cedar tone transparent stain now the house is getting dark and cleaning staining again would make the Julius even darker. so I’m considering stripping and then using a brightner to neutralize the stripper. The house is cedar shakes and cedar board and batten

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