Timber treatments

Experienced renovator Michael Holmes advises on the best solutions for dealing with wood decay in timber frame houses.

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Experienced renovator Michael Holmes advises on the best solutions for dealing with wood decay in timber frame houses.

Left to nature in damp conditions, timber will decay fairly rapidly once dead, disintegrating into little more than dust after being digested by insects and fungi. Leave untreated timber in a building in damp conditions, and much the same process of decay will set in, which is why damp is the enemy of the homeowner. It is also the reason most timber used in construction today is either softwood treated with insecticides and fungicides to preserve it, or hardwood, which is more dense and resinous, and more naturally resistant to decay.

Once decay has set in, it is important to identify the cause correctly and treat it accordingly, followed by undertaking repairs to any structural elements that have been extensively damaged. A structural engineer will be able to assess the extent of damage and suggest the remedial action that is required. It is also usual to treat the rest of the building with insecticides and fungicides to prevent re-infection.

Identifying decay

Dry rot: Sends out fungal strands along timber and through damp walls or plaster. The first sign is a musty smell. Once established, the strands resemble white or grey cotton wool. It forms a fleshy, ochre-coloured fruiting body when very established.

Wet rot: Less serious than dry rot, as the strands do not spread through walls, this can still damage damp timber rapidly. There are two common types of wet rot: brown rot causes timber to darken and crack in a cuboidal pattern, turning it very crumbly, while white rot causes wood to lighten in colour and turn fibrous.

Woodworm: There are several species of woodboring insect, the most common of which is the furniture beetle. This can be identified by the small, round holes that are left on the surface of the timber (1.5–2mm in diameter) and the dust that it leaves behind from boring. Deathwatch beetle tends to infest oak, elm, walnut, chestnut, elder and beech and can be identifi ed by bore holes of around 3mm – larger than the holes left by woodworm.

In the UK, house longhorn beetle infestations are usually found only in Surrey and southwest London. Damage is usually to the sapwood of softwood and can be recognised by 6–10mm oval, often ragged, holes. Larval activity may be audible as a scraping sound.

Treating decay

If a building is kept dry and well ventilated, the problem of timber decay will eventually resolve itself and infestation will die back. This is the ecological approach to solving the problem, together with treatment with Borax salts as a preservative. More often, chemicals containing insecticides and fungicides are used to provide a rapid solution that kills the infestation. This is carried out by specialists (contact the Property Care Association, 0844 375 4301, propertycare.org). Chemical treatment will cost from £600–£1,000 upwards, depending on the extent of the infestation.