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Effective dry rot control requires all infected timber to be removed and all infected masonry to be sterilised.
Although removal or sterilization of infected material would in theory achieve control, in practice it is often impossible to identify precisely all infection and impracticable to remove or sterilise all affected material. The essence of effective control is the prompt restoration and future maintenance of dry conditions.
Infected and decayed wood removed from a building should be treated with preservative or burnt on site
As a matter of good practice infected timber should be removed from any building with damp conditions. However once removed it can be temporarily and safely stored outside on site provided that it is not adjacent to the walls of any buildings. Disposal to a local authority site poses no hazards, although contamination of hardcore with decayed wood can lead to decay problems in new construction. Treated wood might be regarded by local authorities as toxic waste and unauthorised disposal to a landfill site therefore could be illegal. Burning infected, untreated timber on site is common practice but it is not necessary as a means of removing any decay risk to existing buildings.
Dry rot spores on oversites beneath suspended timber ground floors must be sterilised by spraying with dry rot masonry fluid.
Dry rot spores on an oversite cannot result in the spread of the fungus unless timber, card or paper debris are present on or in the oversite. If such debris is present in an infected building, it may well already be infected and must be removed.
Serpula Lacrymans, the only so called dry rot fungus, is a particular species of brown rot. Affected wood is brown and shows cuboidal cracking; the 'cubes are usually 25mm2 or more in size and tend to be larger than those of other brown rot types, requires the same minimum moisture content of about 22% for decay to progress.
Particular features of the dry rot fungus call for special consideration when specifying remedial work. Dry rot has a higher tolerance of alkaline conditions than the wet which allows it to spread through porous masonry materials in older properties. Wet rot fungi, although able to grow over the surface of non-wood materials, rarely grow through masonry materials.
The dry rot mycelium and strands are often found growing at the interface between brickwork and lime-sand plaster. They may also be found in the mortar joints. This growth can only take place through relatively old lime mortars and lime plasters where the alkalinity has become reduced over time. High alkalinity, as found in fresh lime or cement mortar, will normally prevent growth through mortar joints, although growth over the surface of new brickwork is still possible. Fruit-bodies frequently appear on infected masonry surfaces, often in positions apparently remote from decaying timber.
The fungus derives no nutrition from masonry and causes no significant damage to the infected masonry to other damp timbers in contact with the infected wall. (Growth rates equivalent to almost 1 m per year have been recorded in buildings, and, with time, the fungus can spread several meters through masonry.) For this reason prompt remedial action is required after the discovery of dry rot
Dry rot growth through masonry can only be sustained if both a timber food source and dampness are present. Removal of all timber from contact with an infected damp wall, and drying of the wall and associated timber, will therefore prevent further spread of and damage by the fungus. However, during drying of infected walls fruit bodies may appear it is also important to appreciate that the fungus may lie dormant in dry timbers, including small fragments within dry walls, for up to a year and possibly longer in cooler areas such as cellar; and that if damp conditions are allowed to return to fungus may become active again.
Although the strands of the dry rot fungus can conduct moisture and fungus can conduct moisture and nutrients to support growth, this ability is dependent on the moisture conditions in the surrounding wood or masonry. The fungus cannot colonise dry, well ventilated wood or masonry. However, the ability to conduct moisture does allow the fungus to spread from an attack in damp timber into adjacent, poorly ventilated voids where is is able to introduce additional water to marginally damp timber which might otherwise remain just below the moisture threshold for decay. Further more, gloss paints and other impervious coatings can trap moisture in masonry or stud walls. This will then allow the fungus to introduce sufficient moisture for the fungal mycelium to spread progressively through the coated masonry or timber. By this process the fungus can spread through voids such as those beneath poorly ventilated ground floors or behind painted internal panelling.
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