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Identifying rot

Identifying rot

For any rot to begin within a property there needs to a certain level of dampness in timbers to allow wood damaging fungi to become established. The moisture level of the timber needs to be above 20% for spores to grow.

The microscopic spores from the fungi travel on air currents and if they land on suitably damp wood (particularly if the wood is untreated) they will germinate and start to feed on the timbers.

Hyphal threads called mycelium develop from the fungi spores and spread through the wood extracting nutrients and weakening the timbers.

Two common types of rot are Dry Rot and Wet Rot. They begin in similar ways but require differing treatments, so it’s vital to get a professional diagnosis to ensure effective treatment. Rot treatment will generally require the removal and replacement of decayed wood with treated timber, along with spraying of anti-fungal solutions on adjacent timbers.

Wet Rot – is a general term describing most fungal species responsible for timber decay. They attack wood that has become damp and remains full of moisture. There are two common wet rot species in the UK, Cellar Fungus (Coniophora puteana) and Mine Fungus (Fibroporia vaillantii). These tend to occur more often than dry rot but are more likely to be localised to the source of water ingress. For example flooding, leaking pipework or defective guttering can lead to wet rot problems.

Dry Rot – the wood attacked by dry rot (Serpula lacrymans) gradually perishes as enzymes produced by the fungus feed on the cellulose in the timber. This leads to deep cracks appearing in the wood and the decaying timbers appearing powdery when dry. Dry rot needs less moisture than wet rot, so leaking gutters or timbers in contact with damp masonry can be enough to initiate the spores. It also has the ability to spread far from its source, as the mycelium strands can grow through materials such as mortar, plaster and brick to reach other timbers some distance from the original infestation. This makes dry rot more difficult to eliminate.

There is no guaranteed way to prevent rot, but good building maintenance; including keeping the property watertight, free from damp and rectifying any defects as soon as they become apparent can help to protect your property from rot problems.


About the author

Property Care is a specialised division of Rentokil working in the field of woodworm treatment and damp proofing for over 60 years. We work with residential and commercial customers across Britain, covering areas from London to Glasgow, and provide house surveys for home buyers.

Rentokil technicians provide specialist treatments for rising damp, dry rot and cavity wall ties as well as dealing with damage caused by wood boring beetles. Download our brochure for more information on “Protecting properties against Woodworm, Damp and Rot“.

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