How to Treat Untreated Wood for Outdoor Use

How to Treat Untreated Wood for Outdoor Use

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Wood is one of the best materials you can work with. But if you don’t look after it, this material will deteriorate and rot away.

If your project is outside, you will need to treat the wood in some way. If you do, it will last for a long time and keep its appearance as well.

This article will explain how to treat untreated wood for outdoor use, so keep reading to find out all about this process.

5 Best Ways to Treat Untreated Wood for Outdoor Use

There are a few different methods you can use to preserve your wood. In this section, we’ll outline the most common approaches.

Method #1: Use Linseed or Tung Oil

Oils work by penetrating the wood and seeping into the grain to provide protection. Both linseed and tung oil are naturally occurring. Seeds from the tung tree make tung oil and flax seeds make linseed oil. While these oils provide protection on their own, they are often mixed with polyurethane, and mineral spirits, to create an outdoor finish.

A quick note on safety: when working with and applying these types of oil, be very careful with wet, oily, rags. It’s important to lay the rags out flat, in a well-ventilated area away from flammable materials. This is because the rags can combust if they are scrunched up and allowed to dry.

Applying the Treatment

In this section, we’ll discuss the process of treating your exterior timber with linseed or tung oil.

The list of tools you’ll need includes tung or linseed oil,  mineral spirits, polyurethane, a mixing stick, a paintbrush or roller, sandpaper, and rags.

Step 1: Mix the oil with polyurethane and mineral spirits in equal measure. Stir until they are completely mixed.

Step 2: Use a roller or paintbrush to apply the finish onto the wood. Make sure to work it in, with the final strokes going with the grain. Leave the oil to soak into the wood for a couple of minutes. Keep watching the surface and, if it starts to dry, apply more oil to these patches.

Step 3: Remove any excess. For the oil that doesn’t soak into the wood after a few minutes, wipe it off with a rag.

Step 4: Leave the finish to dry and cure. You need to give the oil enough time to dry before working with it more. In a separate article I wrote more about tung oil drying time.

Step 5: sand the wood back with fine sandpaper, 180-grit or higher.

Step 6: Repeat the previous steps to build up layers of finish on the wood at least twice.

Method #2: Use an Exterior Lacquer, Epoxy, or Varnish

There are a lot of finishes available on the market that are specifically created for exterior use. Three of the most common finishes are lacquer, epoxy, and varnish. The exact application of each of these will vary depending on the exact product, however, there are some common elements that we’ll explain in this section.

Before any work can take place applying the finish, there are some preparation stages to complete. Firstly, make sure that the wood is sanded and mark-free. Secondly, clean the surface and make sure it is free from dirt and dust.

For this method, you will need your finish of choice, a mixing stick, a paintbrush or roller, sandpaper, and clean rags.

Applying the Treatment

Step 1: Stir the finish. Some finishes can separate if not used for a long time so use the mixing stick to stir the finish lightly.

Step 2: Use the roller or paintbrush to apply the finish to the timber. You can spread the finish across the grain, but make sure to do the final strokes with the grain.

Step 3: Wait for the finish to dry. Check the packaging of the finish to see how long it needs to dry. Some environmental factors such as temperature and airflow will impact drying time. Make sure the wood is covered and safe from water if it’s outside.

Step 4: Cut the finish back with fine sandpaper. Use at least 180-grit.

Step 5: Clean away any dirt, debris, and dust that has settled over the surface after sanding.

Step 6: Apply further coats. You want at least 3 coats on the wood to protect it from the elements. To do further coats, simply repeat steps 1-6.

Method #3: Use an All-In-One

When finishing, a lot of the time people have to complete a multiple staged process. To get the tone and coloring they want, they use a stain. Then to protect the wood from the outside, they use a sealant or preservative. The trouble with using two different products is that there’s always a risk that they might not work together. This is why an all-in-one stain and sealant combination is a good choice for many people.

Applying an all-in-one stain will change depending on the manufacturer, so it’s important to always check the packaging and instructions before starting. However, following the steps outlined in method 2 will often be the best process.

Method #4: Wood Paint

When people come to the end of their woodworking projects, they often forget one of the best wood protectors out there: wood paint. Understandably, a lot of the time woodworkers would prefer to show off the natural grain and texture of the timber instead of covering it up with paint. However, sometimes, paint is the perfect finish.

With wood paint, you can add some vibrancy and color to your project. It’s quick and often quite cheap to apply paint. Alongside this, if there are a few mistakes in your project, you can use a filler and cover it up with paint. For the purists out there, this isn’t the best option, but sometimes it’s the cheapest and fasted option.

Paint protects wood by creating a barrier between the exterior weather conditions and the timber itself. Water, moisture, and bugs struggle to penetrate the best types of exterior wood paint, meaning that the wood can last a long time.

Traditionally, paint is applied with a brush, however, if you want a smoother, cleaner look, consider using a roller or even a spray gun. A brushed finish lends itself very well to cottage and rustic styles. Usually, you should apply multiple coats of paint, allowing it to dry in between each application. In a separate article, we wrote about paint drying times.

Method #5: Wood Preserver

A wood preserver does exactly as the name suggests: it preserves wood. Wood preserver comes in either clear or pigmented options and waterproofs timber, alongside keeping decay and rot at bay. Further characteristics of a good wood preserver are protection against algae, mold, and woodworms. Lastly, a wood preserver helps to reduce UV damage to the wood.

You can apply wood preserver in a few different ways, however, the best option is to soak it. Soaking the timber allows it to pull the preserver deep within itself, so protection is not just on the surface. If you are unable to soak the entirety of the wood, try just soaking the end grain, particularly parts that are in contact with the ground.

When you can’t soak wood at all, use a brush to coat the material liberally, multiple times. Depending on the manufacturer’s instructions, this should be repeated at least twice.

How Can You Tell If Your Wood Is Untreated?

The more you know a specific species of timber, the better you will get at understanding if it is in a natural state, or if there’s treatment added to it.

Treated timber can display a number of properties. For example, a different color, film on the surface, chemical smell, or oily feel all indicate a treatment has been used. Alongside this, wood that is pressure treated will be clearly labeled with either a stamp or tags, denoting what treatment it has gone through.

How Long Does Untreated Wood Last Outside?

In this section, we’ll provide rough guidelines for how long untreated wood lasts outside. However, it’s important to remember that these can vary drastically. Environmental conditions such as temperature, humidity, rainfall, and pests all have an effect on how long timber can last outside.


There are a lot of different pine varieties in the world. But on average, this wood has a lifespan of 5-10 years.


Cedar is considered a hardy wood and can last between 15 and 20 years untreated outside.


Oak is well known as a great choice for exterior work and is often sought after by timber framers. Untreated, oak can last between 15-25 years outside.


Spruce doesn’t cope well outside when not treated. Untreated spruce can last between 3 and 5 years.

Mistakes to Avoid, Tips & Tricks

To make wood last longer outside, there are a lot of techniques you can incorporate. In this section, we’ll discuss some of the mistakes to avoid as well as tips and tricks.

Don’t Have Wood In Direct Contact With the Ground

Wood in direct contact with the ground is going to rot more quickly. The moisture from the earth will seep into it and cause the wood to degrade. In larger building work, like houses, there will usually be an impermeable membrane of some sort to stop dampness rising through the timbers.

Don’t Have Wood Constantly Wet

If a piece of wood is underneath a leaking drainpipe, the constant water will cause it to degrade, rot, and fall apart.

Regularly Reapply Treatment

The key to long life spans for exterior wood is to keep a regular maintenance schedule. Treating the timber once will extend its life well beyond the untreated timescale, but retreating the timber means that the protective qualities of your treatment won’t fade away and leave the wood exposed to harm.

Quality of Timber

The better the timber you choose, the longer it will last. Try to avoid any wood that has a lot of knots, shakes, and splits.


Treating your timber is a vital step if you want to look after it and make it last a long time. There are a lot of options available to treat your timber, with many made for very specific situations, so make sure to do your research to find the perfect match.