What is pressure treatment and how does it protect wood?

Within the garden buildings sector, the term ‘pressure treated’ or ‘pressure treatment’ may be a phrase you hear banded about a lot.

In this article, we’ve broken it down into simple terms for you. Hopefully, with the information we provide, you’ll be able to make an informed decision on what you want to do with your garden shed, log cabin or summerhouse.

A natural product

Wood is a natural material, which unfortunately means it is susceptible to rotting, decay and other changes. When wood is part of a tree, you won’t notice any changes to it. This is because the tree is rooted in the ground, which means that the wood can’t move easily.

Once wood is crafted into planks and batons, however, it’s a different story. The wood can bend and change shape. In the gardening industry, this is called warping or bowing. You may have seen this in action if you own any wooden household items. For example, if you’ve ever had a wooden chopping board that all of a sudden doesn’t lie flat on the worktop, it’s probably because it has absorbed water while being washed.

Wet wood especially also attracts insects and bugs, who feed on the damp timber. You’ll know, if you’ve ever lifted up a log, how much woodlice and similar creatures love the soggy, dark conditions that wood provides.

If your wood is looked after properly, however, problems like these can be avoided.


Since the mid-2000s, the main chemical component of pressure treatment solution has been copper. Copper inhibits the growth of fungus and microbes and stops mould and mildew in it’s tracks. It really is a magical metal. Copper also oxidises enzymes, lipids and proteins, making them reactive and toxic and so not suitable for any living, such as termites, to thrive around.

Wood preservative

Wood preserver, and the practice of preserving wood, has been around for centuries. You can buy tins of wood preserver which you apply to the shed yourself, like paint. If you don’t opt for pressure treatment, you will need to treat your wood manually at least once per year. However, even if you do practice this, the wood will not be as resilient as it wood be with pressure treatment.

Industrial procedures used in pressure treatment cannot be replicated at home. This is why we recommend you purchase pressure treatment with any of our buildings, and save yourself the hassle of treating it yourself!

Pressure treated wood

Pressure treating is colloquially known as ‘tanalising’. This name stems from the use of a branded pressure treatment solution called ‘Tanalith E’. Not every company uses the same solution, however, for treating their wood.

The process that takes place within tall, cylindrical vats that are laid flat on the ground. This means that the top is lying sideways. The wood, which is usually in batches of thin planks wrapped together, can then be wheeled into the cylinders.

Once the wood is in the cylinders, the doors are secured shut. The next step is the creation of a vacuum within the tank. All of the air is removed from the cylinder. Then the solution is poured into the vat.

Once the wood is immersed in the liquid, a further vacuum is created to increase the pressure inside the tank – hence the name. This forces the liquid further inside of the wood than it would naturally go. As the liquid is absorbed, the chemicals become rooted in the grain of the wood. Pressure treatment is a far more rigorous preservation process and protects the wood in a far more reliable way than would be achieved with a simple paint-on preserver.

Treatment with pressure

Pressure treated wood appears a natural green colour after the process is complete. This is because the copper in the solution has reacted with the air. Eventually this green colour will fade to the original light sandy-brown colour of natural softwood. It certainly doesn’t mean your wood is mouldy!

It then takes a lengthy amount of time for the wood to dry out completely. At Garden Buildings Direct, we sometimes vacuum wrap the pressure treated wood before it is entirely free of moisture. This sometimes leads to the common misconception that the wood is rotting, or has been left out in the rain when it is delivered to the customer. Rest assured that it is not rotting! Instead, the mere fact it is green, or wet, will mean that it fares a lot better against the elements and against being left outside.

Pressure treated garden shed
The new BillyOh Switch comes pressure treated as standard.

Pressure treatment can protect wood from rot for many, many years. At Garden Buildings Direct, we offer a ten-year anti rot guarantee on most of our buildings, but with pressure treatment, this guarantee is extended to fifteen years. You’ll be able to tell how long your guarantee is from the sticker icon located on the image of the product on its page.

Some of our buildings are now offered with pressure treatment as standard. This includes the new BillyOh Switch Pent shed and the BillyOh Planthouse Potting Shed.

Can I paint a pressure treated shed?

Yes. You can still paint or stain a shed that has been pressure treated, meaning you won’t have to settle for the natural colouring if it’s not your style. The only thing you have to be aware of is the moisture within the wood. Before you paint, make sure that the wood is completely dry. Whether it’s a matter of days or weeks, this is integral to the painting process.┬áThis is because oil-based paints will repel the water and will not set to the wood, and water based paints will not be absorbed into the wood, due to the moisture blocking its path.

Hopefully with this guide we’ve given you an insight into the process of pressure treatment, and explained why it’s great! There are only a few of our buildings on which we don’t offer pressure treatment. You can find out whether we do on your building of choice by heading to the ‘Select Treatment’ section of the product page. Thanks for taking the time to check out our article!

For more helpful guides and advice, head to our blog.