dry rot

A damaged wall with fruit bodies

Dry rot refers to the decay of timber in buildings and other wooden structures caused by certain fungi. In other fields, the term has also been applied to the decay of crop plants by fungi and the deterioration of rubber. It would appear to be a paradoxical term seemingly indicating decay of a substance without the presence of water. However, its historical usage dates back to the distinction between decay of cured wood in construction, i.e. dry wood, versus decay of wood in living or newly felled trees, i.e. wet wood^[1]. In addition, the term can be used as a metaphor for grave underlying problems within a large organization (such as political corruption in government or low morale in the armed forces) that show no symptoms until a sudden, catastrophic failure, much as dry rot of wood in ships caused catastrophic failure.

The term is most commonly used in reference to the decay of building timbers. It refers to damage inflicted by either: Serpula lacrymans (formerly Merulius lacrymans) predominantly in the United Kingdom and northern Europe; and/or Meruliporia incrassata (which has a number of synonyms, including Poria incrassata and Serpula incrassata) in North America. Both species of fungus cause brown rot decay, preferentially removing cellulose and hemicellulose from the timber leaving a brittle matrix of modified lignin. Eventually the decay can cause instability and collapse in houses, wooden ships' hulls, and other wooden structures.

When applied to these fungi, the term is a somewhat misleading misnomer as both species require an elevated moisture content to initiate an attack on timber (28–30%). Once established, the fungi can remain active in timber with a moisture content of more than 30% – in the same way as other timber decay fungi using the brown rot decay mechanism.

The perpetual saturation of wood with water inhibits dry rot, as does perpetual dryness.^{[citation needed]}

Historical use of term

‘Dry rot’ is an eighteenth century term for a brown rot. The term was used because the damage was thought to be caused by internal ‘fermentations’ rather than water.

The (London) Times on Tuesday 12 March 1793 carried an advertisement that informs the reader that the British Colour Company, No. 32, Walbrook, London continues to use, manufacture and sell paints prepared with the Oil of Coal, which is of a very penetrating nature, and hardens wood in an uncommon degree protecting it from weather, dry rot and ice. ^[2]

In the early nineteenth century the rapid increase in instances of timber decay attributed to dry rot (brown rot) in the British naval fleet brought the term into wider usage. Thomas Wade's 'A Treatise on the Dry Rot in Timber' was published posthumously by the Navy Office in 1815 following his investigation of the matter in ships from various countries.^[3] The second HMS Queen Charlotte was launched in 1810 and, when inspected, the timbers of the upper decks were found to be infected with 'the dry rot'. By 1816 the cost of repairs for this vessel had exceeded the ship's original construction cost.^[4]

Texts published in the nineteenth century and early twentieth centuries restrict the term to fungi which produced substantial (white coloured) mycelium including; Antrodia (Fibroporia) viallantii. Eventually, the term came to apply to only one or two fungi: the main one being Serpula lacrymans, which subsequently became known as 'true dry rot'.

Schilling & Jellison^[5] note the potential efficiency of these 'dry rot' fungi in growing away from moisture sources, although there is no reference for how efficient a brown rot fungus has to be at translocating water in order to be classed a 'dry rot' and Schilling^[6] suggests efficient nutrient translocation and utilization, notably nitrogen and iron, may be more distinctive in these species than water translocation. Water translocated in this fashion carries nutrients to the extremities of the organism; not, as is sometimes inferred, to render dry timber wet enough to attack. Coggins^[7] goes into more detail about water movement in S. lacrymans.

Treatment (of timber decay fungi identified as 'dry rot')

There are epoxy treatments available that kill rot by filling in the channels of the damaged wood, killing the rot and restoring structural integrity. Commercial anti-freeze is also very effective at preventing dry rot formation as well as killing the fungus. Certain copper compounds, such as copper naphthenate, are available as a brushable solution and are frequently used when dry-rot damage is repaired by splicing in new wood; after removal of bulk rotten wood the remaining original surface is saturated with such a compound (typically green in color) before application of the new wood.

In certain buildings, particularly those with solid 9 inch (or greater) brickwork and those built using lime mortar and flint (commonly known as bungeroosh in the Sussex area), dry rot has been known to travel through and along the wall surface behind plaster and render. It is therefore recommended that where dry rot is found, plaster and wall coverings should be stripped back to a metre past the infestation in all directions, and the whole area treated. However, given that dry rot attacks only wet timber, common sense should dictate that plaster need not be removed where there is no timber or any timber is dry (outside the zone of wetting that caused the outbreak). Identifying the source of water and allowing the affected timbers to dry will kill dry rot, as it is a fungus and requires water as all fungi do. Furthermore, plaster should not be stripped back in any historically important building without advice from those who do not have a vested interest in making money from selling treatments.

References

See also

• Brown rot of fruits