Fungal decay caused by wood decaying fungi (wood rot)

When carrying out a termite inspection or pre-purchase inspection, the detection of above normal moisture levels is a vital part of the report. Many building problems that will arise in the timber pest industry are moisture related. More importantly if a timber pest problem does not exist at the time of the inspection, but above normal moisture levels are detected, you can just about guarantee that further down the track a timber pest problem will arise.

The majority of fungi that can have an effect on wood will produce spores. These spores will serve a similar role as seeds of a plant. However spores are very light, microscopic in size & can potentially be produced in the millions. Because of their size & weight they can be transported great distances. Most of these spores will land on an unsuitable surface & do nothing. The spores that do land on a wood surface with a moisture content of approximately 28-30% will begin to germinate. This will initiate the complex process of fungal growth, the breakdown of cellulose &/or lignin in the timber to a more soluble compound & ultimately wood decay fungi.

The key requirements of wood decay fungi are;

(1) A wood food source - Some timbers are more durable to wood decay fungi than others. But no untreated timber is regarded as completely immune.

(2) Oxygen - In most situations the process of fungal growth leading to wood decay fungi will occur at a normal oxygen level.

(3) Moisture - This is a key element for the growth of wood decay fungi & can be produced around the home by situations such as poor building design, lack of ventilation, faulty plumbing &/or drainage etc. It is important to note that fungal decay cannot develop where the moisture content in the timber is below 20%.

(4) A suitable temperature - This will vary due to the differing species of wood decay fungi. The range for most species will range from 25 – 30 degrees. However one particular species of wood decay fungi has a requirement of only 20 degrees.

Some examples of fungal decay are;

(1) Brown Rot Fungi - This is also known as brown cubical rot due to the characteristic damage that it causes. As a result of this type of decay, the wood will shrink and crack into rough cubical pieces. Another result of this fungal decay is that it will produce a brown discoloration. This brown discoloration is due to the fungi breaking down the cellulose in the timber, exposing another component of the timber lignin. This lignin will not be affected. This can typically cause the remaining timber to show a darker colour than it was before the attack (hence the name brown rot fungi or cubical brown rot).

(2) White Rot Fungi - This type of fungi attacks both the cellulose & lignin of the timber. White-rot fungi are able to produce enzymes needed to break down lignin and other complex organic molecules. This type of fungi will initially attack the lignin of the wood. Once the lignin is digested, the fungi will destroy the cellulose and other major parts of the timber cells. The decayed wood with the remaining cellulose will be off white in color. Another characteristic is that the remaining timber will appear fibrous, stringy, and spongy (hence the name white rot fungi or white stringy rot fungi).

(3) Soft Rot Fungi - These organisms are a mixture of fungi & bacteria. They are typically inhabitants of soil. They will attack the cell walls of timber. This leads to the formation of microscopic cavities inside the wood, and sometimes to a discoloration and cracking pattern similar to that of brown rot fungi i.e. it will also produce cubing. However these "cubes" will be mostly smaller than those found in brown rot fungi.

(4) Mould Fungi – The spores of these fungi are also airborne & their behavior is similar to the fungi described above in that they will land on timber & germinate when a moisture content of approximately 28- 30% exists. However the key difference here is that they do not decay timber. Any damage caused will generally be very superficial. The presence of mould and their spores may be the cause of health problems in humans. It may cause allergic reactions such as asthma and dermatitis. Usually the presence of mould fungi alerts an inspector to a ventilation &/or moisture problem. If these situations are not addressed & not rectified it may lead to further problems such as allowing other fungal decay to establish itself & flourish. The continuation of any moisture & ventilation problems will also cause other timber pest problems.

Some ways of reducing moisture related problems are;

(1) Rising damp – Rising damp gains its moisture source from dampness in the soil. This moisture is absorbed via porous building materials such as the buildings brickwork, concrete slab, building piers etc. It should be recognized during a termite inspection or pre-purchase inspection so that it may be addressed by a licensed tradesperson specializing in that field. The purpose of addressing this situation is to provide a barrier between the moisture source & the porous material drawing at this moisture. This is achieved by the placement of either a physical &/or chemical application where possible.

(2) Subfloor ventilation – In buildings that have raised flooring, the amount, type & placement of ventilators will determine the amount of humidity & ventilation of the air beneath the flooring. The placement of these ventilators must ensure that there is adequate cross ventilation & that there are no dead spots (areas of low ventilation) present.

(3) Water drainage – All areas of water drainage need to be reported when performing a termite inspection or pre-purchase inspection. These areas may be due to poorly installed or broken plumbing, poor drainage around the external walls &/or subfloor of the building, deterioration of the guttering/storm water drainage system, runoff from higher ground levels etc. Detection of these problems & rectifications need to be performed where possible to reduce the threat to the building from timber pests.

(4) The use of preservatised timbers – the best way to reduce the threat of fungal decay in relation to construction timbers is by reducing the moisture content of the environment in which the timber is to be utilized. However some timbers such as transmission poles, fences & landscaping/retaining timbers can be purchased that have been treated. However it is important to note that even treated timber in constant contact with soil & high moisture levels may still be considered to be at risk.