Timber Treatments
Importance of Identification
Not all fungi found in buildings cause wood rot. However, the presence of any fungal growths indicate that damp conditions exist which are also suitable for the development of wood rotting species and some remedial measure may be necessary to remove the source of dampness.
Types of Wood Rotting Fungi
There are two main types of wood rotting fungi found in buildings:
Dry Rot "Serpula Lacrymans"
General: Mostly Softwoods
Major building decay fungus often causing extensive damage. A brown rot, which typically occurs on wood, embedded in, or in contact with wet brickwork. Sensitive to height temperatures (over 25c) and drying and therefore rarely found on exposed timbers or situations where fluctuating conditions are likely, e.g. well ventilated sub-floors and roofing timbers. It is able to grow through bricks and mortar, though cannot feed on these. Strands can transport moisture from damp areas, allowing spread of the fungus to dry woo in unventilated conditions. Appearance of fruit-body may be the first indication of an outbreak.
Checking for moisture in timber is vitally important to protect against or find fungal decay and beetle attack.
Damage CharacteristicsDecayed wood, dull brown in colour. Deep cracks along and across the grain, light in weight and crumbles between the fingers, these are all typical features. No skin of sound wood.
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Fungal Characteristics:
"Mycelium"
Silky white sheets or cotton wool like white cushions with patches of lemon yellow or lilac tinges where exposed to light. In less humid conditions forms thin, felted grey skin. During active growth the advancing hyphal edge forms a silky fringe.
"Strands"White to grey, branching, sometimes as thick as a pencil, brittle when dry.
"Fruit-Body"Usually on wood/wall joint, rare on exterior of building. Tough, fleshy, pancake or bracket shaped. Centre is yellow-ochre when young, darkening to rusty red when mature owing to spore production, covered with shallow pores or folds; margin white or grey.
Wet Rot
General: SoftwoodsTogether this group are a common cause of rot in damp woodwork in buildings frequently in areas of higher temperatures, and can cause extensive damage (particularly Fibroporia Vaillantii)
Damage CharacteristicsResembles Serpula Lacrymans (Dry Rot) - Wood breaks up into cubical pieces however, decayed wood is lighter in colour and cracks are not as deep as those caused by Serpula Lacrymans.
Fungal Characteristics:
Mycelium
White or cream sheets or fern-like growths, may discolour brown on contact with iron.
StrandsSeldom thicker than twine, white to cream in colour and remain flexible when dry (only well developed in Fibroporia Vaillantii)
Fruit - BodyIrregular lumpy sheets or plates, white or cream to pale yellow, spore bearing surface white to pale yellow in colour, occasionally with pink patches (Poria Placenta only), with numerous minuet pores.
It is not necessary to distinguish between the many species of wet rot, since the same remedial measures are required for all species. However, the successful remedial treatment of dry rot may require more elaborate measures.
Identification of Wood Boring Insects
A number of small insects, mainly beetles, are able to use wood as a food source and some of them can cause serious damage to building timbers. These insects all have fairly similar life cycles, although there are variations. Use the above menu for more information on Wood-Boring insects.
In a beam end where the end is damp, removal of moisture and targeted treatments into the heart of the infestation are the only way of eradication.
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Investigation into the extent of the damage is necessary and is achieved by micro-drilling.
The face of this moulded timber plate appeared to have a moderate infestation by Death Watch Beetle (Xestobium rufovillosum). When the back of the timber was investigated it was completely destroyed. Lead work behind the plate had become porous, pDry Rot Dry rot’ Serpula lacrymans is a fungus that decays wood. The name derived from serpent like and the tear ducts which produce moisture. The discovery of dry rot in a property can be very worrying to a property owner. Dry Rot is a destructive fungus but with professional surveying and remedial works it is completely treatable.
All wood-rotting fungi require both food (wood or other cellulosic material) and water, and the dry rot fungus is no exception; deprived of either, it cannot survive.
There is a lot of mythology surrounding dry rot fungus which is founded on the ability of its strands to penetrate through non-wood building materials, to transport water to otherwise dry area. The strands do transport water but they have to be in a humid unventilated situation otherwise water will evaporate very quickly. Dry rot will only grow in ideal conditions and once discovered and exposed / ventilated will form sporophores to try and propagate in other ideal situations by throwing spores into the air.
The worst outbreaks are normally found in buildings under or behind unventilated floors and timber walls with a source of moisture and a high humidity. Another common cause is timber building elements built directly into damp masonry.
CONTROL MEASURES
Diagnosis of any sources of moisture by a qualified timber surveyor is critical to curing Dry Rot.
Because of the nature of dry rot it is important that the opening up (removal of floors and plaster) to investigate the extent of the outbreak is carried out under the supervision of the qualified Maclennan-LSE remedial surveyor so as the full extent of the Dry Rot can be ascertained and drawn and mapped out but without causing unnecessary destruction to unaffected areas and finishes which may be unnecessary or of historical importance.
If an area of timber or plaster affected by Dry Rot is of historical importance then every effort should be made to conserve it by drying, isolating and if necessary treating with Boron. The area or building element should then be monitored either visually or with Dry Rot sensors and damp sensors which are now available through Maclennan-LSE.
Isolation of all timbers from damp masonry is essential as a long term cure for the Dry Rot.
Treatment with Boron can be carried out to help prevent further outbreaks. As a masonry biocide B10 will effectively eradicate spores and Fungal Growth in the wall. B20 will work very effectively on damp masonry and will remain in dry wood as a defense should it become damp at which point the B20 would move into the wood to give further protection.
All new timber used in repairs should be pre-treated with a wood preservative. Detailed guidance on the treatment required for various timber components is given in the British Standard BS 5268: Part 5, which deals specifically with structural timber, and BS 5589 which covers a wider range of uses.
Guidance is also given on the use of naturally durable timbers (see also Digest 429 published by the Building Research Establishment Ltd). probably as a result of litchen on the roof above.
Death Watch Beetle
Maclennan-LSE have treated major death watch infestations in public building, churches and domestic properties over the last 25 years.
The only effective treatment is as a result of a thorough investigative inspection which involves drilling and probing of all at risk timbers.
Maclennan-LSE treatment of Death Watch Beetle is always targeted and involves drilling and injecting a Permerthin based paste to eradicate the lava and Boron to deal with the associated fugal decay.
Maclennan-LSE guarantee treatment of accessible timbers for a period of 30 years, Maclennan-LSE welcome the opportunity to present a seminar on the subject of timber treatments for building professionals.
Catagories of Wood Boring
InsectsInfestation by wood-boring insects does not always indicate a need for remedial treatment. Infestation commonly found in building timbers fall into three categories according to the treatment normally required.
Catagory ATreatment usually required. Common Furniture Beetle (Anobium Punctatum), House Long Horn Beetle, Death Watch Beetle (Xestobium Rufovillosum).
Catagory BControl of dampness, decay, Ventilation required, some localised treatment might be necessary. Wood Weevil (Pentarthrum Huttoni).
Catagory CNo treatment required. Bark Borer (Ernobius Mollis), Forest Long Horn Beetle, Sawply, Wood wasp, Jewel Beetle, Marine Borer.
