Insights into long-term Weathering Tests

Ten years of testing is 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 really perform after years in the elements.

Now, ten years later, the results are providing rare, real-world evidence for Teknos, joinery manufacturers, specifiers, and the wider coatings industry.

Why outdoor testing matters

Accelerated weather testing in laboratories offer controlled conditions, but they cannot replicate the complex conditions of real-world testing.

Panels were prepared according to EN 927-3, a European standard test for assessing the durability of coatings on wood over 1 year. They were mounted at a 45° south-facing angle, with sharp edges included to accelerate coating breakdown.

But one year was simply not enough to have any significant impact on the coatings. So, Teknos and Accsys decided to extend the testing period to 3 years, 5 years, and now 10 years.

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

Teknos have also been running test sites for over 10 years in Denmark, the UK, and Malaysia to give further climatic perspectives.

What has been tested

The trial included a wide variety 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 of the findings confirmed expectations – More dimensionally stable substrates, such as Accoya and Tricoya, proved reduced dimensional movement in the timber, put less stress on the coating and extended performance.

Less easy to predict, was the effect of care and maintenance. Regular cleaning, even with just water and a sponge, showed a marked improvement in surface appearance and performance over time.

According to Justin Peckham, Regional Head of Sales at Accsys: “One thing we’ve seen consistently here is that the coatings are lasting significantly longer on Accoya and Tricoya than on the other more unstable 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 relied upon over the long term. For homeowners, it translates into better advice on care and maintenance, which could lead to lower lifetime costs. But for the wider industry, the biggest contribution may be confidence: evidence that warranties and performance statements are not simply marketing claims, but backed by real-world data.

Looking ahead

The panels remain in the field. Some will be recoated and returned for further exposure, allowing the programme to continue building a picture of long-term performance. As product development specialist Alireza Boustani explains, “On most of the samples we still see a very good coating performance even after ten years. The idea is to continue outdoor exposure of those samples.”

Ten years is a milestone, but the work is far from finished. With more timber types, more coating systems, and more climates to assess, outdoor testing continues to provide lessons that no laboratory can replicate.

Teknos Paint – Teknos