Abbott Damp Proofing : Dry/wet Rot

The decay of timber in contact with dampness is generally due to fungal attack. There are two main categories of fungal attack found in buildings - dry rot and wet rot. Both types of attack require a moisture content in excess of 20% in the timber and are usually found in poorly ventilated areas. Wet rot is generally more prevalent in timbers with a significantly higher moisture content but is not as serious a problem as dry rot. Very often dry rot and wet rot can be confused and it is therefore very important a C.S.R.T. qualified remedial surveyor determine the nature of the attack.

Dry Rot
Dry rot (Serpula lacrymans) is one of the most serious threats a property has. If left unchecked it can lead to extensive damage both to the timbers and masonry.Once established dry rot can spread through areas of a property that are not damp.

An aggressive dry rot attack

An aggressive dry rot attack in a cellar.

An aggressive dry rot attack

Dry rot generally establishes itself in areas where there is a lack of ventilation but a readily available moisture source exists such as a leaking pipe or rainwater simply entering the property due to blocked drains, blocked guttering or surface water gaining access through defective masonry or poorly sited air bricks. Sub-floor areas are one of the most common places for an outbreak to start. Dry rot feeds on the cellulose content of timber leaving it weakened often to the point of structural collapse.

There are four possible components to a dry rot outbreak: hyphae, mycelium, sporophores and spores. One or all of these can be present in any given outbreak.

The hyphae or strands are usually off-white in colour and have the appearance of a root system. Their purpose is to transfer nourishment through the other components of the fungus and to search out new food sources. The mycelium usually takes more of a sheet or skin form but there are variations depending on conditions. It is usually accompanied by a mushroom type smell. The sporophore or fruiting body is the reproductive mechanism of the fungus. It appears either plate or bracket shaped and has a rusty red appearance usually with a pale off-white perimeter. Other colours such as lilac can also be present. The sporophore ultimately bursts to release thousands of rusty red spores over the surrounding areas. The spores are the individual ‘seeds’ each with the potential of creating a new outbreak of dry rot.

The treatment of Dry Rot
Dry rot treatment has to be extensive. All traces of the fungus should ideally be removed. All directly affected timbers and timbers in contact with affected areas should be replaced. Affected masonry should be treated by sterilisation involving drilling holes to facilitate the introduction of a biocide deep in to the walls. Sub floor areas need to be scraped and cleaned to remove any spores.

All re-instatement work has to incorporate biocide treated materials from the timber to the mortar. Any new plasterwork should also be chemically modified.

As well as undertaking extensive dry rot treatment it is vitally important the conditions that lead to the dry rot outbreak are corrected. Ventilation should be improved and the moisture source removed.

The treatment schedule for a dry rot outbreak will vary from property to property. It is therefore important a full survey be carried out to assess the work required.

Wet Rot There are numerous types of wet rot. Although they have their own characteristics and may attack timber in different ways they all have common features the most important of which being they all limit their attack to damp timber. Unlike dry rot, there is no threat to masonry or dry timbers In view of this, extensive chemical treatment is not generally necessary and remedial action is directed towards removing the moisture source, improving ventilation and replacing affected timbers.	Wet Rot & Woodworm affecting a floor joist.

	Ceiling timbers affected by wet rot.