Timber Rot Treatment



 The true dry rot Serpula lacrymans is an incredibly versatile, pernicious and adaptable fungus which, given suitable conditions, will in a remarkably short period, destroy structural timbers and other mater containing cellulose within a building.

Dry rot is a misleading name as the fungus will only occur in damp situations where timber has a moisture content of between 20% and 40%.

The spores of Serpula lacrymans are present in the air and become deposited onto timber. These spores can remain dormant over long periods until, given the correct conditions, they germinate and form mycelium which usually looks like cotton wool.

The first indication of an attack is often the appearance of open cracks in painted joinery such as skirting boards, wall panelling or door frames.  The timber shrinks back and both horizontal and vertical cracks appear on the surface. Usually a white rubbery cushion will develop along the edges of the timber, this being the beginning of a sporophore or fruiting body which bears the spores.


The points of identification of Serpula lacrymans are:

  • The appearance of the affected wood, which warps, shrinks and cracks both longitudinally and vertically to form cubing of wood.  The wood can be crushed in the fingers.                                                                                                                                                                                                                                                
  • The presence of a rust-red spore dust.  If the fungus is an advanced growth and has produced a sporophore, the surrounding area may be covered with fine red dust consisting of millions of spores.
  • The appearance of the sporophore, which varies in shape and is dependent largely on the position in which this fruiting body develops.  If the sporophore is fully developed the characteristic rust-red spores will easily identify it. This generally appears as a pancake-like plate or a thick, broad bracket.  When very young it may look like a white or grey rubbery ball or beading along the edge of the skirting boars, picture rails etc.  As it grows, it usually becomes tinged with a lilac coloration, but when it is ripe the hymenal surface becomes reddish brown with spores.  Sporophores vary in size from a few centimetres to a metre or more in length and width.
  • The texture of the sporohore is soft, leathery, cold and rather clammy.  It is not pleasant to handle and feels like something dead. When old, the texture becomes harder and tougher and the colour darkens until it is almost black.
  • Smell – the odour of active Dry rot is quite characteristic and once identified will not be forgotten. It is a “mushroomy” smell.  If the fruiting bodies are old and decaying the odour is decidedly unpleasant.
  • Mycelium.  If the wood is decayed and o sporophores have appeared on the surface then the mycelium growing on the hidden side of panelling, skirting boards, door and window linings, flooring etc over joists, rafters, plates or any hidden wood and over contacting brickwork, masonry, site concrete or soil, will identify dry rot.
  • Under very moist conditions and where the fungus is very fresh, dry rot mycelium looks like soft white cushions of cotton wool with glistening drops of water clinging to the surface, thus giving it the scientific name Lacrymans weeping). This will show patches of yellow and lilac soon after it is exposed to the light. As it grows older or the conditions become drier, the mycelium adheres to the timber in mouse grey silky skin with strands or rhizomorphs at the edges.  These strands, when dry, are invariably brittle, unlike those of other strand forming fungi such as Fibroporia vaillantii.  This is a useful distinguishing feature.


An outbreak of dry rot will only occur where there is a good food source, usually timber, although cardboard boxes and general paper debris can also be suitable materials a they also contain cellulose.  In addition to the food source a moisture content of 20% to 40% must be present to start the attack.  Once the fungus is growing however, it has the ability to transfer moisture into wood which is drier.

It will flourish in unventilated and humid conditions, which are often encountered in concealed areas.

It therefore follows, that outbreaks of dry rot are often caused by the presence of damp such as overflowing lavatory cisterns, plumbing leaks, rising damp, steam, condensation, defective flashings and inadequately ventilated underfloor areas etc.

Permanent wetness rarely causes dry rot.  It is usually after a leak or water source has been checked and the conditions restored to something approaching normal that an outbreak will start to develop.

Dry rot is difficult from the other common timber destroying fungi, in that it has the ability to grow over and through non nutrient material.  It an humidify the ambient atmosphere for its vigorous growth in stagnant conditions, and its growth will cease where the ventilation is good.


It is usually impossible to ascertain the full extent of fungal growth without thorough and ruthless exposure. Experience is needed to provide intelligent guesses regarding likely areas of infection and usually only when structures are completely exposed as part of the treatment can a full assessment be realized.

It should also be borne I mind that dry rot is a quick growing fungus.  Unless treatment is effected shortly after discovery its spread can be rapid and costly to repair.


All plaster and render should be stripped off a wall surface for at least one metre (39”) beyond visible hyphal strands and a brick or stone removed at intervals to ensure that the fungus is not travelling through the walls, this particularly applies where a cavity exists in the wall. The hyphal strands will grow between the plaster and structural wall face and travel through mortar joints.

All decayed timbers, together with those set into or against affected masonry should be removed and burnt.  Adjacent solid floors should be taken up and contaminated site soil should be removed over an area at least one metre (39”) beyond the last visible hyphal strands.


The affected brickwork and masonry should be drilled at 225mm (9”) centres and wall surfaces wire brushed to remove all traces of fungal strands.

Brickwork and masonry should be surface sprayed and the drilled holes injected under pressure with dry rot fluid.  The site soil should similarly be surface sprayed.  There is no need to remove the whole length of a joist or rafter because the end is affected, it should be cut half a metre (19”) beyond the visible sign of growth or decay.  This however does not apply to timbers which are set against the affected wall or which have contact with the wall along their length. These should be entirely removed to ensure growth does not extend behind.

All remaining timbers should be sprayed with fungicide for at least two metres beyond the limit of the outbreak and ideally the whole room area should be similarly treated. Sawn ends should be liberally dowsed.  The use of fungicidal paste and injector valves are also effective agents in these situations.



All necessary repairs to roofs, rendering, pointing, rainwater goods, cills etc must be carried out to ensure the elimination of water ingress.

If no damp proof course exists or the original one has broken down a new one should be installed (see separate information sheet).  Ventilation may need to be improved. Any timber used in reinstatement should be pre treated and saw ends should be generously dowsed with fungicide.  Where possible replacement timbers should not be built into affected walls and should be supported independently with ends kept clear of these wall surfaces.  Replacement timber should be insulated from direct contact with masonry by bedding onto damp proof course material and ends should not be cemented into walls.

Suspended timber ground floors affected by Dry Rot are usually better replaced with solid concrete construction incorporating a damp proof membrane. The use of polythene is not recommended for this purpose.


We are an established Company which has been operating since 1967. We have a first lass reputation gained during this period Our work is recommended and accepted by Local Authorities, Architects, Surveyors, Building Societies and other specifying bodies.


Timber Decay Treatment Limited have experienced Surveyors, one of whom will visit your property to carry out a full and detailed inspection, report on the findings and recommend suitable eradication measures.

GUARANTEES (where applicable)

Timber Decay Treatment Limited’s own 10 year warranties are underwritten and protected by a separate independent guarantee. Double protection is therefore assured. Both documents are transferable to any subsequent purchaser of your property.


Chemicals used in the formulation of the fluids we apply are those considered most environmentally acceptable and are approved for professional use by the Health and Safety Executive. Work is carried out in accordance with the Government’s C.O.S.H.H. regulations.


Timber Decay Treatment Limited are members of The Property Care Association.  Work undertaken by us is carried out in accordance with a strict code of practice.  You can be assured that the work will be properly executed and the Building Societies and Local Authorities will accept our standards.  It should be noted that these memberships are normally the minimum qualification required of treatment Companies by the above bodis for mortgage and grant purposes.

CALL TDT PRESERVATION – 01761 416 728 


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