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Dry Rot

Dry Rot

The most serious type of decay is dry rot, which refers to wood decay caused by the fungus Serpula Lacrymans. The fungus forms on timber with a moisture content of above 30%, which allows the fungus to grow at an accelerated rate; causing severe damage to a building’s structural timbers.

Successful control and eradication of dry rot requires carefully planned measures. It is extremely important that an outbreak is correctly identified; dry rot can be particularly difficult to detect in its early stages as it usually develops beneath floorboards, behind panelling or plaster. There are a number of features to look for when identifying the possible presence of dry rot, such as softening of the wood and, in certain areas, dry rot causes shrinkage and distortion. Timber that has been severely affected by dry rot will be much lighter in weight and usually disintegrates in the palm of your hand; the timber no longer has a fresh resinous smell but a more distinctive mushroom odour.

Identifying Dry Rot

Identifying dry rot can prove difficult as it usually develops out of sight; however, if you suspect your home has fallen victim to this vicious fungus, here is what to look for:

The fruit-bodies may be the first indication of an outbreak of dry rot. Fruit-bodies resemble the shape of a pancake: their texture is fleshy (when fresh) and brittle (when dry) and the centre is covered with a series of folds from which spores are produced. The outer edge remains light in colour but the centre becomes a rusty red when spore production starts.

Wood that has been affected by dry rot will often shrink and split into brick like pieces, similar to the appearance of charred wood but not as dark in colour. The damaged wood cannot by itself be used to successfully identify the fungus as wood that has been affected by dry rot shares similar characteristics with wood that has been affected by wet rot. Like most fungi, dry rot grows by elongation and branching of delicate filaments known as Hyphae, these are known as the Mycelium and usually appear as a fluffy white growth or as white or grey sheet depending on the humidity of the area. Water droplets are often produced on the surface of the mycelium and this feature gives the fungus its name “Lacrymans”, from the Latin for tears. Furthermore, bright lemon yellow patches may also be seen, but these are more common, together with tinges of lilac, in less humid conditions. Dry rot retrieves food and water through grey or white branching strands that are formed behind the Hyphae. These strands can vary between 2-8 mm in thickness and become brittle when dried, a feature which can be used to distinguish dry rot strands and similar strands caused by wet rot.

Dry Rot experts Swindon, Wiltshire
Dry Rot company Swindon, Wiltshire
Dry Rot Swindon, Wiltshire

Characteristic Features of Wood Destroying Fungi

Type of Decay: Dry Rot

    • Fungus: Serpula Lacrymans
    • Effects on Wood: Rotted wood shrinks and splits into cubical pieces by deep cross cracking. Generally occurs in damp conditions. Spore dust is a light rusty colour.
    • Visible Strands: Strands are grey, sometimes as thick as pencil, and become brittle when dried.
    • Other Growths: Often occurring in damp conditions, soft white cushions or silky tassels can form. In drier conditions, silver/grey sheets usually displaying patches of lemon yellow and tinges of lilac.
    • Fruit Bodies: Fleshy, soft but rather tough; shaped liked pancakes. A spore bearing surface with a reddish brown tinge, with wide pore or labyrinth ridges and a white, outer margin.

Type of Decay: Wet Rot

  • Fungus: Coniophora Puteana
  • Effects on Wood: Causes darkening and longitudinal cracking. Cross cracks are often covered by a thick surface of relatively sound wood; often occurring in very damp conditions.
  • Visible Strands: Strands are slender and usually thread like. In early stages can appear yellow in colour, developing into a deep brown/nearly black colour when mature.
  • Other Growths: Occasionally very thin, skin-like growths; can appear yellow or dark brown. Commonly occurring beneath impervious floor coverings.
  • Fruit Bodies: Rarely found in buildings. Has a sheet-like shape; the spore bearing surface is often an olive-brown colour.

Type of Decay: Wet Rot

  • Fungus: Poria Vailantii
  • Effects on Wood: Rot is similar but less widespread than that of dry rot. Various species of Poria can occur in houses, most of which require more moisture than dry rot.
  • Visible Strands: Strands are often white or whitish; seldom thicker than twine and remain flexible when dried.
  • Other Growths: White or cream sheet, or fern-like growths.
  • Fruit Bodies: Shaped like sheets or plates and are white in colour. The spore bearing surface is also often white, showing numerous, minute pores.

Type of Decay: Wet Rot

  • Fungus: Phellinus Contiguus
  • Effects on Wood: There is no cubical cross cracking. Bleaches the wood, which eventually develops a stringy, fibrous appearance.
  • Visible Strands: There are no strands.
  • Other Growths: Brown, tufted growths, which are commonly found within voids or on the surface.
  • Fruit Bodies: Tough, brown growths; often elongated. The surface is covered with minute pores.

Ability to Spread

Besides the ability to spread on wood and other cellulosic materials, the dry rot fungus also grows on the surface and within substrates such as brick and plaster. The growth over these materials is sustained purely from the fungi’s ability to transport dissolved nutrients through the branching strands. Given suitable conditions dry rot growth can extend several metres from its food source through plaster and masonry. The dry rot fungus has a limited capability for further growth once its food source is removed or exhausted. If the fungi’s original food source becomes exhausted before the fungus reaches new timber it will die, if new timber is encountered this will act as a new food source and allow the outbreak to spread further. In well designed and maintained buildings, the moisture of internal timbers will usually remain below 20% and therefore there is no risk of dry rot or wet rot. However, risks develop when building defects lead to wetting of timber; where wetting has occurred damp, still air will encourage the growth of the fungus, especially if these conditions are maintained for long periods.

Specialist timber treatments should be carried out in strict accordance with the PCA Code of Practice for Remedial Timber Treatment by an experienced and qualified technician.

Biocraft South West use specially formulated preservatives that allow for the successful eradication of dry rot. To arrange a survey of your property or for further information regarding timber decay contact us today. We cover Andover, Bath, Bristol, Chippenham, Devizes, Marlborough, Oxford, Salisbury, Swindon, Trowbridge and Warminster.

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