Dry Rot Treatments

Dry rot is the decay of wood caused by the fungus Serpula lacrymans, which if left, can have devastating effects within a building. Diagnosis of dry rot in a building has the ability to strike terror into the heart of the recipient of this dismal news. However, to the untrained eye dry rot and wet rot can easily be confused. It is therefore essential that a correct diagnosis of a timber decay / fungal decay problem is paramount this can be confirmed by using one of Pennine Preservation's skilled surveyor's.

Dry rot has the potential to cause serious damaging decay in timber found in buildings throughout the UK, but it does not have to be devastating or outrageously costly to cure if caught in time.

A careful diagnostic survey carried out by Pennine Preservation's (a dry rot control company or damp proofing and timber treatment specialist) is required to identify if the timber decay is dry rot or wet rot, to locate and cure the source of dampness, to control or treat in a very selective and targeted way and to re-instate with appropriately pre-treated or naturally durable replacement timber.

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. Much of the mythology surrounding dry rot is founded on the ability of its strands to penetrate through non-wood building materials, to transport water to otherwise dry areas and for the fungus to 'manufacture' its own water. In reality, the delicate hyphae are the primary colonisers and the ability to conduct water is limited and can be counteracted by good ventilation.

The process of timber decay itself produces water but in this respect dry rot is no different from any other wood-rotting fungus and, likewise, its ability to produce moisture in this manner can be counteracted by ventilation. Decay will cease if the moisture content of the wood is reduced to below about 20 per cent, and many extinct outbreaks of dry rot are discovered in buildings where the fungus has died out as a result of this happening, probably following building maintenance which has eliminated a source of moisture.

DRY ROT CONTROL

Because of the total dependency of dry rot on moisture, the primary control strategy must be based on environmental considerations aiming to restore and maintain dry conditions.

A detailed dry rot survey should be carried out by a qualified damp and timber surveyor to identify and locate sources of moisture ingress. Particular attention will be paid to roofs and rainwater systems with emphasis on gutters and downpipes, parapet roofs and roof coverings. Rain penetration can also be through renderings and flashing's or around windows and doors. Rising dampness through missing, bridged or otherwise defective damp-proof courses must be rectified. Any plumbing should also be inspected for leaks.

Rapid drying should be promoted through the provision of ventilation and heating which may also require specific building work to prevent moisture ingress and transfer, and to encourage aeration. Dehumidifiers can remove moisture from the air but their effectiveness in aiding drying of walls depends on the rate of evaporation from the wall surfaces.

In many cases drying will take a long time, often taking years, especially where some types of older buildings are affected. Therefore, secondary measures will often be required to prevent further damage by the fungus before it is effectively arrested by the drying process.

ASSESSING THE DRY ROT OUTBREAK

Once dry rot has been correctly diagnosed, it is necessary to determine how far the dry rot has spread. All woodwork in the vicinity of any outbreaks should be inspected by a qualified damp and timber surveyor (CTIS or CSRT) to assess the extent of decay and the current moisture content of the timber. Extensive removal of plaster is necessary only if it is suspected that timber is embedded in the walls and is at risk.

REMOVING TIMBER AFFECTED BY DRY ROT

Removal of all timber affected by dry rot is destructive but necessary in principle. Retaining affected timber presents problems for the structural integrity of the building and falling debris can be a hazard to occupants and others if decay continues. Timber already below 20 per cent moisture content presents little risk of further decay. Special building measures are necessary if timber is to be retained, including isolation from damp masonry by way of incorporating a damp proof membrane or using metal joist hangers etc.

DRY ROT TIMBER PRESERVATIVE TREATMENT

Liquid preservatives can be applied to the surface of sound timbers left in situ to help prevent new infections developing.
If timber infected with dry rot has to be retained for special reasons and decay cannot be arrested in the short term by drying, preservative treatments that penetrate throughout the affected part of the timber can be used.

For example:

  • application of a preservative paste
  • repeated addition of liquid preservative to sloping holes drilled into the wood or by pressure injectionli
  • insertion of boron rods or tablets (these are only effective if the wood is wet).
  • Second item

MASONRY TREATMENT FOR DRY ROT

Although the dry rot strands can travel across masonry, the dry rot fungus derives no nourishment from it. The concept of killing the fungus within masonry by wide-spread irrigation with a fungicide traditionally has provided a 'comfort factor', but it has to be questioned in each case whether this procedure can be justified. First, it is usually difficult to achieve a thorough treatment and, secondly, the treatments introduce large quantities of water which then needs to be removed, increasing the risk of damage to the masonry, as well as prolonging the time it takes to dry the structure.

The most important role of chemical treatments of the masonry is to prevent the fungus from obtaining access to a fresh food supply in the form of timber in adjacent areas, or replacement timbers being introduced into the area. For this purpose, localised chemical treatments of the masonry (cordon sanitaire) can create a useful barrier between the fungus on the wall and the wood.

Examples of such treatments are:

  • surface application of fungicidal fluid
  • use of fungicidal renderings
  • application of preservative pastes
  • localised irrigation treatments.

THE COST OF TREATING DRY ROT

We are often asked - How much does dry rot treatment cost / How much does it cost to treat dry rot?

The cost of treating dry rot or the cost of dry rot control will vary with each individual outbreak of the dry rot fungus. Firstly, a dry rot survey has to be carried out by a fully qualified CSRT damp and timber surveyor to correctly identify the fungal decay and determine if it really is dry rot and not wet rot as it is so commonly misdiagnosed by those who are inexperienced.

The extent of the dry rot has to be determined, as this timber decaying fungus can spread behind wall plaster and under floors without being noticed until it attacks another piece of timber, such as a skirting board or door/window frame, elsewhere. The source of the dry rot outbreak also has to be determined.

It is therefore not possible to provide a cost of treating dry rot without carrying out a detailed dry rot survey.

MONITORING FOR DRY ROT

Maintenance and monitoring of the conditions in buildings cannot be stressed enough. Dry rot develops very slowly, so early detection and curing of moisture ingress will prevent decay occurring in the long term. Routine monitoring can be as simple as regular visual inspection to check the integrity of the building fabric against ingress of moisture.

TYPICAL SYMPTOMS OF DRY ROT INCLUDE:

  • Wood shrinks, darkens and cracks in a 'cuboidal' manner
  • A silky grey to mushroom coloured skin frequently tinged with patches of lilac and yellow often develops under less humid conditions. This 'skin' can be peeled like a mushroom.
  • White, fluffy 'cottonwool' mycelium develops under humid conditions. 'Teardrops' may develop on the growth.
  • Strands develop in the mycelium; these are brittle and dry and crack when bent.
  • Fruiting bodies are a soft, fleshy pancake or bracket with an orange-ochre surface. The surface has wide pores.
  • Rust red coloured spore dust originating from the fruiting bodies. Commonly described as looking like brick dust.
  • Active decay produces a musty, damp odour.