For log houses, saunas, and other log structures—as well as wooden construction in general—bacteria and fungi can cause significant damage by promoting decay and mould growth. These processes affect the aesthetic appearance of the building and, importantly, can be harmful to health. The primary measure to prevent bacterial and fungal growth is proper ventilation of the wood. Treatments such as impregnations, antiseptics, and other products serve as preventive chemical protection. However, even with these treatments, there is no 100% guarantee that the impregnation was applied correctly or that the builders followed the strictest instructions. Biological processes can occur if the wood moisture content reaches 20% or higher and the temperature exceeds 22°C.
Mould fungi are microscopic parasitic organisms. Their spores, like pollen, are carried through the air. To reiterate, they are a problem in warm, damp, and poorly ventilated spaces. The first signs of mould include blueing, greening, peeling walls, lichens, and black spots. Mould colonies can appear in different colors: Alternaria and Aspergillus niger – black or brown; Penicillium – blue or green. Mould can also appear in shades of grey, yellow, and red.
One of the most dangerous fungi is the dry rot fungus (Serpula lacrymans), whose first signs are yellow or pink fuzz. Later, a white, fluffy mycelium appears, sometimes with yellowish or pink creamy patches, eventually forming a wrinkled gray film. This fungus spreads extremely quickly, with the mycelium capable of growing several centimeters per day. Unlike other domestic fungi, true dry rot can destroy even dry wood. Moist wood is only required for initial establishment; afterward, the fungus itself releases water. It destroys both softwood and hardwood, as well as organic materials such as leather, carpets, and oil-painted artworks. Untreated wood can also be attacked by the white rot fungus (Poria vaporaria), whose white, cotton-like mycelium has branching, rounded, fuzzy strands 4–6 mm thick. Its fruiting body is firmly attached to the wood and resembles a branched cushion. White rot is typically found in cellars, damp rooms, attic structures, and floor joists, attacking wood stored in forests that has become damp. The cellar fungus (Coniophora puteana) is nearly as destructive as true dry rot and white rot fungi. Its mycelium develops relatively weakly, often forming soft, thin films, and usually lacks hyphal cords. The fruiting body is initially whitish, later turning dark brown with white edges. The upper surface of the fruiting body is generally smooth, occasionally slightly wavy.
Other fungal forms and their Latin names include: mosses, unicellular algae, mould fungi, wood-decaying fungi, brown rot, house mould – Coniophora puteana; true dry rot – Serpula lacrymans; white rot fungus – Antrodia vaillantii; sulphur polypore – Laetiporus sulphureus; oak bracket – Daedalea quercina; sapstain fungus – Lentinus lepideus; green stain fungus – Gloeophyllum sepiarium; white rot fungi – Bjerkandera adusta, Trametes hirsuta, Coprinus sp., Coprinus lagopides, Coprinus lagopus, Coprinus atramentarius, Schizophyllum commune, Crepidotus variabilis, Pluteus cervinus, Hypholoma radicosum, Marasmius sp., Mycena galariculata, Entoloma confetendum; slime molds – myxomycetes (Lycogala epidendrum, Fuligo septica).
The causes of all these mould fungi include: roof leaks, defects in waterproofing, absence or improper installation of rainwater drainage systems, contact with the ground, nearby vegetation, poor ventilation, and poorly or incorrectly constructed structural joints.
This information has been prepared on the initiative of the Log House Manufacturers Association, based on practical knowledge, comments, and observations from professionals, and in collaboration with the Department of Materials Engineering at KTU.
