Mould can grow on a wide range of different organic materials, such as textiles, leather, paper, and also wood. Mould is not a description of a particular fungus species, but an umbrella term for all fungal mycelia and their spore carriers growing on the surface of a given material.
On wood, mould usually populates the surface and feeds on freely available sugars and other organic substances. It doesn’t destroy the substance of the wood and causes no structural weakening. However, the discolouration caused by mould can lead to a considerable loss in value for many wood products. In addition, mould spores released into the air can pose a serious health risk, especially when mould occurs indoors.
What kinds of mould can grow on wood?
There are currently 20,000 known mould fungi. Those occurring on wood belong to the Deuteromycetes, Acomycetes or Zygomycetes groups. Important species are: Aspergillus, Penicillium, Trichoderma, Epicoccum, Mucor and Fusarium.
How is the wood attacked?
Mould fungal spores can be found in the air everywhere. To germinate on any substrate, they need sufficient moisture and warmth. The absolute moisture content is not decisive, but the amount of freely available water in the substrate. Wood is a hygroscopic material and absorbs moisture from the air. If wood is stored in a relatively humid environment for a longer period, it absorbs sufficient moisture to enable fungal spores to germinate.
The continued growth of the mould is influenced by substrate moisture, relative humidity, temperature and the available nutrients contained in the substrate. For example, mould grows quickly on the cut ends of freshly felled trees. Particularly at risk here is the sapwood, because the available nutrients are found in its rays. Badly stacked and stored rough sawn timbers also allow mould to grow quickly, as does timber that is insufficiently dried and stored in air-tight storage containers, such as wood being transported in the cargo holds of ships.
What damage can mould do?
Mould initially attacks only the surface of the wood but can, during the course of its development, penetrate a few millimetres into the wood’s interior. The hyphae are colourless so mould does not lead to any discolouration. The coloured spores, however, do lead to stains on the wood’s outer surface that cannot always be washed off completely, leaving so-called mould stains. Though these stains reduce the value of the wood, they can be removed by planing if necessary.
How can mould be prevented?
To prevent mould and infestation from other wood-staining fungi, freshly cut timbers must be dried quickly. When stored in saw mills, the risk of mould infestation in freshly cut timber is especially high. Temporarily effective, environmentally compatible anti-sapstain products protect the wood during the drying phase and prevent massive losses in its value.