Over the past twenty years, thermally modified wood has been positioned in Europe as a sustainable alternative to tropical hardwood. Manufacturers often refer to the European standard EN 350 to classify their wood into durability classes. But what many people don't know is that the laboratory tests on which these claims are based were, until recently, incomplete. Since 2020, the new standard (EN 113-2:2020) has required a third, critical fungal species that primarily tests thermally modified wood for its weak points. Time to lay the facts on the table.

The situation before 2020: EN 113:1996
Until 2020, the biological durability of wood was tested using the old EN 113:1996 standard.
This test consisted of a laboratory setup in which wood samples were exposed to two basidiomycetes (fungi):

Coniophora puteana (brown rot)
Trametes versicolor (white rot)
Based on these two fungi, the wood was classified into durability classes according to EN 350.

Problem:
Standards are usually only updated when practical experience shows them to be insufficiently reliable.
This also applies here.

The original fungal combination in the durability tests was originally intended to assess natural wood species, not modified materials.
Significant damage from these fungi was observed in untreated softer wood species or untreated bamboo fibers.
When thermal modification emerged, it seemed like the solution: thermally modified wood and even bamboo composites suddenly scored (very) well in these tests and could claim high durability classes according to EN350.

But was that realistic?

The fungi used in the old standard didn't test for the weaknesses created by thermal modification.
This modification changes the structure of the wood, but doesn't make it immune to all fungal species.
Critical fungi, such as Rhodonia placenta, were simply not included in the test.

It's like testing the brakes of a car while it's stationary.
Of course, everything seems fine, but the result was unrealistic.

December 2020: The standard change - EN 113-2:2020

In December 2020, the old, unrealistic standard was withdrawn and the latest, current standard was launched: EN 113-2:2020.
This new version has a clearer purpose: correctly determining the natural durability of untreated and modified wood or wood products.

Main change:

In addition to the well-known fungi (Coniophora puteana and Trametes versicolor), "Rhodonia placenta" (formerly Poria placenta) has now been mandatory added as a third fungus for thermally modified products.

Why Rhodonia placenta?

Rhodonia placenta is an aggressive brown rot fungus known for its ability to degrade thermally modified wood and bamboo fibers.
While Coniophora puteana produces relatively few enzymes against hemicelluloses and modified cell walls, Rhodonia does.
Thermal modified wood, bamboo, or other wood products have a weak spot in these areas due to the thermal degradation of their cell structure.

What does this mean for thermally modified wood and bamboo composites?

Many official sustainability claims for thermally modified wood and bamboo composites are based on tests without the presence of "Rhodonia placenta."
The fact that this new, mandatory fungus has a significant impact is confirmed by the adjustment to the standard and the fact that little to no new data or documents have been found since 2020.

Fortunately, considerable scientific research had already been conducted before the standard was updated.
Now that this fungus is mandatory for thermal modifications, scientific studies indicate that the following results are plausible:

A significant decrease in the durability scores of thermally modified wood and bamboo composites (often from classes 1-2 to classes 3-4 or even 5 in some cases).
This impact will be significantly lower for untreated wood species.

The next scientific study is underway.

In our search for Lesser Known Timber Species, we are regularly limited by the availability of general data on wood species.
Sometimes we even encounter untreated wood species with durability classes 1-4.
This distribution is unusual and even illogical.

It's time to test a wide range of untreated wood types ourselves, in accordance with the applicable standard (EN 113-2:2020).
Regardless of the results, we'll then know exactly what we're doing.
We'll likely also include some modified wood types and/or bamboo composite in this test series.
The latter is not yet certain.