A decade in the elements: Teknos explains what 10 years of outdoor testing reveals about timber coatings

10 years of testing are providing rare insights into long-term coating performance

In 2015, a benchmark outdoor exposure programme was established in Arnhem, the Netherlands, to provide data on how timber coatings truly perform after years in the elements. Now, a decade later, the results are delivering rare, real-world evidence for Teknos, joinery manufacturers, specifiers and the wider coatings industry.

Why outdoor testing matters

Accelerated weather testing in laboratories offers controlled conditions, but it can’t fully replicate the complexity of real-world exposure.

Panels were prepared according to EN 927-3, the European standard for assessing the durability of wood coatings over one year. They were mounted at a 45° south-facing angle, with sharp edges included to accelerate coating breakdown.

However, one year proved insufficient to produce significant results. Teknos and Accsys therefore extended the testing period to three years, five years, and now 10.

As Steve Ashton, Technical Services Manager at Teknos, explains: “Certain things simply can’t be replicated in a lab. To truly prove the performance of a coating, real-world testing is the only option.”

Teknos has also operated test sites for more than 10 years in Denmark, the UK and Malaysia to provide further climatic perspectives.

What’s been tested

The trial included a wide range of species and substrates: meranti, merbau, pine, thermally modified timbers, as well as Accoya and Tricoya. Both translucent and opaque coating systems were applied, at varying film builds, to capture how different systems performed in real-world conditions.

What the data shows

Some findings confirmed expectations. More dimensionally stable substrates, such as Accoya and Tricoya, showed reduced timber movement, placed less stress on coatings and extended performance.

Less predictable was the impact of care and maintenance. Regular cleaning – even with just water and a sponge – made a notable difference, improving both surface appearance and long-term performance.

According to Justin Peckham, Regional Head of Sales at Accsys: “One thing we’ve seen consistently is that coatings last significantly longer on Accoya and Tricoya than on other, less stable substrates. The more stable the timber is, the less stress the coating is under.”

Why it matters to the industry

For manufacturers, the results provide reassurance that coating specifications can be trusted over the long term. For homeowners, it means better advice on care and maintenance, potentially lowering lifetime costs. For the wider industry, the greatest value may be confidence: proof that warranties and performance claims are backed by robust, real-world data.

Looking ahead

The panels remain in the field. Some will be recoated and returned for further exposure, extending the dataset and building an even clearer picture of long-term performance.

As product development specialist Alireza Boustani explains: “On most of the samples we still see very good coating performance even after 10 years. The idea is to continue outdoor exposure of those samples.”

10 years marks an important milestone, but the work is far from finished. With more timber types, coating systems and climates still to assess, outdoor testing will continue to deliver lessons no laboratory can replicate.For further information on Teknos, see www.teknos.com.