Moulds and decay causing fungi typically consist of large numbers of fine tubular branch like structures known as hyphae. An interconnected web of these hyphae is known as a mycelium and considered a single organism. The dusty texture of many moulds is caused by large numbers of asexual spores known as conidia formed at the ends of the hyphae. The mode of formation and shape of these spores is traditionally used to classify the mould fungi.

Moulds generally consume sugars in the wood without causing decay. Moulds, by definition, are easily removed from the wood surface by rubbing with the hand. The moulds with which we are most familiar in the home, grow on the interior surfaces of walls and ceilings. They are associated with poor ventilation and heating or excessive interior moisture levels. These kinds of moulds are easily treated with diluted bleach. Clove oil is also very effective at killing Mould spores. Similarly a 1:15 mix of Borax to warm water has also been quoted as killing mould spores.

Brown Rots: are the most common in wet timber framing. They tend to darken the appearance of the timber as they consume the cellulose only, leaving behind the darker lignin. In its early stages the rotted timber may not change much in appearance but can easily be penetrated with a knife. Brown rots are considered to be more ‘malignant’ than other rots because they decay timber more rapidly. One particularly malignant brown rot is dry rot. It has the ability to transport moisture and is very destructive once established.

White Rots: appear to bleach the timber as they consume both the lignin and cellulose. They are less prevalent in softwoods.

Soft Rots:They leave very little indication of their presence. The decay takes place within the cell wall and will generally occur when the timber is in contact with the ground.

A damp wall cavity can form an ideal environment for fungal growth. Typical types of fungi affecting timber are Penicillin, Aspergillus and Stachybotrys. All fungi produce microscopic spores for reproduction that are distributed by wind and water. Large numbers of spores may remain suspended in the air for an indefinite period until they come in contact with a surface. On contact with a suitable wood surface the spores germinate and the hyphae filaments begin to grow, branch and multiply throughout the surface in search of nutrients.

• Timber moisture content (MC) is above 25%. Fungal attack is greatly reduced between 20 - 25% MC, and will typically not occur where the timber MC is below 20%
• Temperatures in the range of 5 - 40^oC (25 - 40^oC is considered optimum). Fungal attack is unlikely to occur at temperatures below 5^oC
• An available food source must be present. Unprotected timber surfaces, particularly sapwood, provides nutrients suitable for fungi to feed upon. Sapwood can readily be protected through the application of fungicides during the production process, or remedial treatments applied during construction
• Oxygen must be present. Timber that is saturated or placed more than 600mm below the surface of the ground is unlikely to be attacked by fungi

• Reduce moisture levels that promote mould growth (remove affected timbers from the source of the moisture)
• Keep timber packs dry when in storage (preferably under cover and not exposed to the rain)
• Ensure timber packs are stored on bearers, above any ground surface moisture
• Where timber is supplied with moisture resistant packaging, ensure that it does not become torn or repair all damage immediately (particularly if exposed to rain and weathering)
• Ensure timbers are treated with fungicidal preservatives appropriate to the Hazard Level for which it will be exposed in service

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