The role and potential of pressure treatment in the wood industry

The use of wood in construction keeps growing because it is renewable and has a low carbon footprint. Wood is combustible, however, so many buildings need it to be fire protected. One way to apply a fire retardant is pressure treatment in an autoclave. This article explains how it works, what it can and cannot do, and what has been tested with SPFR100.

01What is autoclave treatment?

In autoclave treatment the wood is placed in a closed pressure chamber. A vacuum first removes air from the wood cells, then pressure forces the treatment liquid into the wood. Compared with brushing or spraying, the liquid penetrates deeper and the uptake per cubic metre can be controlled batch by batch.

How deep it goes depends on the wood. Pine sapwood takes up liquid well, while spruce and heartwood are much harder to penetrate. Pressure treatment therefore does not automatically protect the whole cross-section, and surfaces that are cut or planed after treatment should be treated again.

02Pressure treatment or surface treatment?

Both can be the right choice. Pressure treatment suits industrial production of larger volumes, such as cladding boards treated before delivery. Surface treatment by spraying, brushing or in a coating line suits smaller volumes, work on site and tinted finishes. What matters for the building is not the method itself but the fire class tested for the exact system: wood species, thickness, uptake or consumption and mounting.

03What has been tested with SPFR100

• Surface treatment: classified B-s1,d0 under EN 13501-1 (classification ET-0388-24) for timber of at least 18 mm, with 240 g/m² in at least two coats.
• Pressure treatment: SBI testing (EN 13823) of pressure-impregnated wood has given results at class B level. A test report is available, but a certified classification for the pressure-treated system has not yet been issued.
• Weathering: SPFR100 has been tested for the durability of its reaction-to-fire performance under EN 16755. Certification has not yet been issued.

If your project requires a certified class, use the classified surface system or ask us about the status of the pressure-treatment classification. We can send the test reports on request.

04Where pressure treatment makes sense

Pressure treatment is worth considering when large volumes of the same profile are treated in a factory, when the timber is machined as little as possible after treatment and when the treatment plant can control uptake for each batch. For façades and interiors where color and appearance matter, surface treatment with tinted SPFR100 is often the simpler choice.

Updated 27.10.2026: clarified the test and classification status.