Fungal decay

The great majority of moulds found in buildings belong to the class Hyphomycetes (Deuteromycotina). They live mainly on starches and free sugars stored in the parenchyma or surface deposits of detritus on masonry, brickwork, concrete, rendering, tiles and paving and on surfaces of damp wood, plaster, wallpaper or paint. Moulds commonly occur on surfaces as a superficial growth causing patchy surface discolouration, usually green, grey, or black, occasionally pink or yellow. Some are rusty red and may be mistaken for spores of S. lacrymans. Others produce a fluffy mass of white growth. Some moulds colonise wood with moisture content at or above 20% but appreciable development requires moisture contents at or above the fibre saturation point (28-32%). Moulds grow best at temperatures ranging from 24-30°C.

Moulds cause some loss in wood toughness by attacking the parenchyma cells, but they usually have only a negligible effect on other strength values. They discolour and seriously weaken such materials as paper, leather, cloth, and fibre-based products such as acoustic tiles, insulation, etc.

Moulds greatly increase the porosity of wood, and moulded wood wets much more easily, increasing the likelihood of decay and moisture-induced deformations. The presence of actively growing moulds serves as an indication that a moisture problem exists, which may or may not present a potential decay hazard.

Common moulds in buildings are:

• Cladosporium species;
• Penicillium species;
• Aspergillus species;
• Trichoderma viride;
• Alternaria species; and
• Aureobasidium pullulans.

Slime moulds

Slime moulds belong to the division Myxomycota, which has a distinct plasmodial state. Myxomycetes are common on fallen trunks and branches on the forest floor. In buildings they are usually found on inorganic substrates such as masonry, brickwork, concrete, rendering, tiles, paving and organic substances such as damp wood, usually exterior joinery. Fruiting bodies are 1-20mm in diameter, variable in appearance from dark green, brown or black to occasionally bright colours, sometimes on stalks or with a silvery skin or uniform coating. All produce masses of brown spores. Myxomycetes feed on bacteria within the wood and become visible only when they produce fruit bodies on the surface.