Have you ever purchased timber with a green tinge? That means you’ve already bought tanalised timber, which is wood pressure-treated with Tanalith E, a preservative forcing protective chemicals deep into the grain to guard against rot, insects, and fungi.
It’s a brilliant choice for outdoor timber in the UK. Here’s why in a bit more detail…
What is Tanalised Timber?
Tanalised timber is softwood that has been treated to extend its lifespan outdoors; typically, the specific softwood is Scots pine or spruce.
When untreated timber is exposed to the Midlands' weather conditions, it will typically rot within a few years. Tanalised timber can last for decades.
It gets its name from Tanalith E, the preservative used in the process; it’s a copper-based compound that binds to the wood fibres and creates a hostile environment for the fungi and insects that can decay the wood.
Ever wondered what that green you see on fencing, decking, and structural posts is? That’s the Tanalith E, a.k.a the reason behind the timber’s long lifespan. Another benefit is that modern Tanalith E is water based and free of arsenic and chromium, which means it is safer than traditional timber preservatives.
Treatment Classes: UC3 vs UC4
Something definitely worth noting is that not all tanalised timber is treated quite the same. There are different levels, also known as classes; the two common ones are:
UC3 - This one is suitable for applications that are still exposed to the weather, but aren’t in direct contact with the ground; examples include fence panels, cladding, decking boards, garden furniture frames, and pergolas.
UC4 - It provides a better level of treatment for timber that will be buried or sitting in water, such as fence posts, gate posts, sleepers, and structural supports.
Can Tanalised Timber Be Painted or Stained?
Yes, but timing matters. Freshly tanalised timber retains moisture from the treatment process and needs to dry out fully before you apply any finish. Painting or staining too soon traps moisture and the finish won't adhere properly.
Once the timber is dry (this can take several weeks depending on conditions), it accepts paint, stain, or decking oil without any issues. A good quality exterior wood stain will complement the preservative treatment and further enhance the timber's lifespan.
Find Treated Timber Online
We hope you now have a better understanding how treated timber is made and why it’s so key in outdoor environments.
A range of treated timber is available at Emerys, with fast delivery to go with it. Get in touch with us today to complete your project successfully.
FAQs
Is tanalised timber safe?
Yes. Modern tanalised timber uses Tanalith E, a copper-based preservative that meets current EU and UK safety standards.
It's safe to handle with normal precautions. Washing hands after use is recommended, as with any treated material.
Can you use tanalised timber indoors?
It's not generally optimal if you’re working in enclosed indoor spaces that lack effective ventilation. For internal structural use in well ventilated areas (floor joists or roof timbers), however, tanalised timber is commonly used. For furniture or surfaces with regular skin contact, untreated or naturally strong timber is preferable here.
How long does tanalised timber last?
UC3-treated timber typically carries a 15-year guarantee above ground. UC4 in-ground timber is rated for 15–30 years, depending on soil conditions and species. Proper maintenance extends this further.