A Finnish university delves into the properties of untreated wood

The stress-reducing effects of wood have a strong influence on people’s well-being. The specific mechanisms behind this phenomenon and how they can be used at a larger scale are currently a hot topic of research at the South-Eastern University of Applied Sciences (XAMK).

Text: Sami Anteroinen
Photographs: Manu Eloaho

Read the article in English: Kaakkois-Suomen ammattikorkeakoulussa pureudutaan pintakäsittelemättömän puupinnan ominaisuuksiin

Katri Martikainen and Milla Sairanen examine cleanliness of a wood surface.

Research indicates that it simply makes sense to use wood surfaces in the interior design of buildings: wood evens out indoor moisture and improves the quality of indoor air. In fact, untreated wood surfaces are even better. What few people realise is that these surfaces tone down the extreme variations in indoor moisture and keep it at an optimal level. In short, wood is sometimes best left alone.

With modern technology, different shapes can easily be machined into wood surfaces to increase their total exposed area. This improves the surface’s ability to gain and release moisture. So-called cross cut wood surfaces absorb and release moisture over three times more effectively than traditional panel surfaces that go with the wood grain.

Finland’s own anti-bacterial trio

Hygiene concerns also call for using wood surfaces. Studies on the anti-bacterial properties of wood surfaces have clearly shown that bacteria deposited on wood surfaces die more quickly than on glass surfaces.

In light of this research, we can see that wood surfaces have an inherent ability to inhibit bacterial growth. Finnish conifers such as pine and spruce in particular have chemical properties with this anti-bacterial characteristic.

It’s strange but true: a dirty-looking pine surface can have significantly fewer microbes than a glass surface that looks sparkling clean.

The tree species and processing method impact the end result

The Wood for Welfare Innovations (PUUSTA) project at XAMK dives head-first into the subject. Work package 1 (TP1) in the PUUSTA project includes “hands-on” investigations into how different tree species promote cleanliness. Since wood’s anti-bacterial properties are better without a surface treatment, this method tests how well untreated wood surfaces can be cleaned.

In the test, Katri Martikainen, an environmental technology student and trainee, pours blueberry soup and a fat mixture over different pieces of wood – and then cleans the surfaces.

These wood surfaces are then assessed: Did microbes remain in the wiped off piece of wood? The process is repeated once a week for 13 weeks. The consulting firm Ramboll will do the final analysis based on the collected information.

– The first phase of the study saw fat and blueberry soup applied to pieces of wood. In the second phase, we only used fat, Martikainen says about the project, which started in August 2021.

Only the best performing materials – pine, spruce, and birch – went on to stage two. The observations made so far indicate that the tree species and surface treatment method have a considerable effect on the result.

– It really is possible to clean the bacteria off the surface, says Martikainen.

Martikainen, who has a Master’s degree in forestry, would like to see untreated wood gain a larger foothold in public spaces.

– It is an ecological and healthy solution that increases well-being, says Martikainen, who finds the smell of wood particularly pleasant herself.

What is moisture buffering?

Milla Sairanen, who is a research engineer at XAMK, is leading work package 2 (TP2) of the PUUSTA project. TP2 studies moisture buffering and thermal comfort properties of wood materials. Sairanen explains that the term “moisture buffering” refers to the ability of a hygroscopic material to absorb moisture from the surrounding air and to release it again.

Milla Sairanen tests the ability of a cross cut wood surface to absorb and release moisture.

– Moisture buffering materials gain or release moisture until they reach the same moisture level as the surrounding air. Sairanen, who has a background in building services engineering, gives a practical example: consider an indoor space with no people or humidity producing equipment. Since the space has no moisture load, the moisture-buffering material releases moisture into the indoor air until the material and air share the same moisture level.

– Likewise, when the indoor space has a moisture load such as people sweating, the moisture-buffering material absorbs moisture from the indoor air.

Buffering applications still in their infancy

Sairanen notes that it is a good idea to recognise the phenomenon of moisture buffering when there is a lot of hygroscopic material in a building as it can affect the control of indoor air moisture and thermal comfort. The field still has a lot to research and develop.

– People talk a lot these days about breathable materials and about how pleasant the indoor air is in wooden buildings. Sairanen, who has brought her expertise to the project for over a year now, notes that moisture buffering plays a role in this but that its systematic applications are still in their infancy.

What kind of wood is the best buffer?

Untreated and cross-cut wood is the answer according to Sairanen.

– On the other hand, you need to take into consideration that untreated wood adds to the fire load.

Towards more pleasant interiors

And what about the other research topic in TP2: thermal comfort – why is this important? Sairanen explains that the term “thermal comfort” refers to how pleasant people find the thermal conditions in their environment. For example, ceramic tile feels quite different from a wooden surface when you walk on it barefoot.

– Humidity affects thermal comfort, as people may consider high or low relative humidity to be unpleasant.

It may well be that the solution lies in moisture buffering: with increased moisture buffering, momentary fluctuations in indoor moisture will be less dramatic and thermal comfort may improve as a result.

The wood for welfare innovations project aims at making wood’s well-being benefits visible and understandable. Through research and development, knowledge is increased on possibilities of wood material in promoting well-being and health.

The main sponsors of the project are The South Savo Regional Council and the European Regional Development Fund (ERDF). Other sponsors are the city of Mikkeli, the South Savo Social and Health Care Authority, Luomoa Oy, Woodi Oy, Uni Development Oy, OiOi Collective Oy and Timberwise Oy.

More information: xamk.fi/puusta