The fungi are a vast group of lower plants everywhere active in Nature, but which are, in the main,

unfamiliar to the average man. He knows of the edible mushroom, and sees, with considerable

suspicion, various toadstools growing in the countryside. He is aware of the moulds and mildews

that grow on jam and damp leather.

While the higher green plants, with which everyone is on familiar terms, are able to build themselves

up by combining the carbon dioxide in the air and water from the soil, the fungi cannot do this, and

must feed directly on organic matter such as animal manure, wood or dead leaves. The fungi are in

fact Nature’s scavengers, consuming unwanted, sometimes harmful, waste material. In the case of

the wood-destroying fungi, they cannot, unfortunately, discriminate between a dead log in a forest

and an equally dead piece of timber built into a house or used as a fence post.

It is for this reason that we are faced with the problems of decay and that the question of wood

preservation is of the first economic importance.

The fungi reproduce themselves by means of minute spores. These are discharged in amazing numbers by the fruiting body (Sporophore), a specialised portion of the fungus. For instance, an edible mushroom three inches across the cap, will produce 1,800,000,000 spores. Since they are so small, the spores are easily carried on the wind, and in the case of the wood destroying fungi it can be taken as a certainty that some spores will encounter every damp piece of timber. When a spore germinates, a fungus plant will establish itself in the wood, ultimately destroying it.

The fungus spore having fallen on a piece of damp wood proceeds to throw out a hollow tube known as a hypha. This pushes its way through the wood and branches and branches again. The mass of these hyphae is called the mycelium, which is in fact the fungus plant. It often happens in cases of wood decay that in early stages there is no outward sign of the fungus to be seen. The hyphae are in the wood feeding upon it. They can only be detected by microscopic examination and even then, it is hard to determine the species of fungus until a fruit body develops, by which time the wood is usually well decayed.

Wood consists of approximately two-thirds cellulose and one third lignin. It is upon the cellulose that

the fungi usually found in house feed. (Certain fungi, the “white rots”, which attack forest trees, consume the lignin as well.) The strands, or hyphae, threading their way through the wood, contains enzymes that are able to convert the cellulose into sugar, which nourish the fungus, giving it the necessary material for further growth and the ultimate production of the fruit bodies, enabling the spread of fungal infection. The dry, brown and brittle substance – it can hardly be called wood – remaining in cases of True Dry Rot, consists of lignin, the cellulose having been consumed by the fungus.

These terms have no precise scientific significance. It is often asked why the term “dry rot” should be

used in connection with a fungus which depends for its existence on wood being wet. The term “dry

rot” is often used for all decay caused by Merulius Lacrymans; to avoid confusion, this is usually referred to as True Dry Rot. However, anyone who has handled wood which has been attacked by True Dry Rot will realise that in its final stage the wood is sufficiently dry and brittle to justify the name. Wet rot properly refers to decay caused by fungi which flourish in damper places, such as Coniophora cerebella and Pori asp.

This fungus is well known for its destruction of timber in buildings, but unlike other fungi which occur in houses, etc. it is not found outside.

True Dry Rot is much more highly specialised for, and much more efficient at, destroying wood than any other fungus. Once established it can spread to wood which, while damp, would be too dry to be attacked by other fungi. It appears to be able to attack timber with a moisture content as low as about 20%, although it flourishes better at about 25% moisture.

The early growth of Merulius, i.e. when the spores first germinate, or at the extremities of the spreading organism, is a fluffy white growth, at first sparse, but then plentiful enough to resemble cotton wool. Later on, the wood appears coated with a dirty grey plate of matted strands. Behind the advancing thin strands, Merulius forms thick strands capable of conducting moisture. This capability for conducting water from one part of the timber to another enables Merulius automatically to adjust the moisture content of wood on which it has gained a foot-hold towards the optimum for rapid decay. Mainly this means wetting wood which is on the dry side, but it is believed that it can also dry wood which is somewhat too wet.

In destroying the wood cellulose, water and carbon dioxide are formed; this water will further assist attack.

The strands of this fungus will penetrate through brickwork or along steel joists in search of further timber, the advancing hyphae being supported via the conducting strands. These strands are particularly dangerous because, even when cut off from the remainder of the fungus, and isolated from timber, as in the centre of a brick wall, they can remain dormant for three or more years under suitable conditions. If new, untreated timber, which is inadequately seasoned and dry, is installed near such strands, they will soon attack it, and the fresh out-break spread.

When the fungus has reached a certain stage of maturity, the fruit bodies are produced. These are generally in the form of flat pancakes, growing on the wood or on brickwork and plaster near it. The fruit bodies have brick-red centres with white edges tinged with lilac. They are sometimes several square feet in area and give off prodigious numbers of spores-2,000,000 a minute from each square foot for several days. It can generally be assumed that where fruit bodies are present, the attack is of long standing.

True Dry Rot-Merulius lacrymans-is therefore the wood-destroying fungus par excellence, and outbreaks of this fungus are more serious and difficult to eradicate than of any other fungus. This is due to a combination of factors.

(i)      Because of its conducting strands, it will spread very rapidly to suitable nearby wood;

(ii)     It will attack wood which is less damp than is necessary for other fungi;

(iii)    Destruction of attacked wood is very rapid;

(iv)    Dormant strands in damp walls, etc., make eradication more difficult.

This is one of the most common wood-destroying fungi. It is found in buildings, and occurs very much more frequently than dry rot, although the extent of each outbreak is usually much less. It is also one of the fungi responsible for the decay of outdoor timber such as fence posts, wooden sheds, etc. It is often present in houses where linoleum has been laid over damp floorboards or where the wood is extremely

wet near leaking pipes, leaking roofs, etc.

Coniophora, as all other wet rots, requires substantially wetter wood for attack to progress than does Merulius. It does not produce well-developed conducting strands, and so will not penetrate brick walls in the Merulius manner.

It is therefore a less serious menace than True Dry Rot, and when the source of damp, which is always associated with an outbreak, is eliminated, the attack is unlikely to start again.

It sometimes happens that where an attack of True Dry Rot is in progress, certain parts of the building will be too wet for this fungus, and in such places Coniophora will be found growing. Oddly enough, although the Cellar Fungus is so widespread, it is rare to find its fruit bodies in buildings.

As its name implies, this fungus is frequently found in damp mines. It is encountered from time to time in buildings but cannot be said to be common. It resembles the Cellar Fungus in the following respects:

•   It attacks wood having a high moisture content; it is found under linoleum and similar floor coverings

•   It is sometimes found growing with True Dry Rot

•   It does not moisten the wood in the course of its growth

•   Once conditions of damp are corrected, fresh attacks

    are unlikely to occur.

This fungus is easily recognized by pure white branching strands, though spectacular growths are rare. The strands, as thick as twine, are tough when dry. True Dry Rot, Merulius, in its early stages, produces white strands, but they may be distinguished from Poria by the fact that they are slight and feathery.

Paxillus Panuoides and Lentinus Lepideus (these fungi have no popular names). They are very occasionally found in buildings, often at the same time as True Dry Rot. They only flourish where the timber is exceptionally damp and when the building is dried out they will disappear.

Fences, gate posts and timber out-buildings are all open to attack. Decay usually starts at ground level, where the wood is always damp, even in the summer. Hardwood, such as Oak gate posts, will rot in time.

There are numbers of fungi which attack timber used out of doors. Lentinus lepideus, mentioned above as being occasionally found in houses, causes much destruction to outdoor softwood timber.

Polystictus versicolor attacks hardwoods, and the fruit bodies must be familiar to most people. They consist of a number of semi-circular brackets, growing horizontally on old tree trunks and logs, one above the other like tiles on a roof, the upper side being attractively coloured with bands of brown and grey.

Stains in timber can be caused by either fungi or chemicals. Of those which are due to fungi, there are two main types-a superficial discolouration due to growth and sporulation of moulds on the surface, and penetrating stains due to growth through the wood of fungi which are themselves coloured, or which otherwise cause apparent colouring of the timber.

Stains due to sapstaining fungi are confined to the sapwood incipient decay may be in both heartwood and sapwood.

The commonest stains are blue stains; these are due to a variety of fungi; a typical example being Cerastostomella pilifera, which affects Scots Pine. They spread both along and across the grain and may eventually permeate the whole sapwood. There may be little or no surface mycelium apparent. Hyphae grow within the wood, they penetrate the cell walls, but holes are very small.

Sapstaining fungi probably draw nourishment from the cell contents (not the cell wall material, as do

decay fungi) and will only develop if the cell cavity contains both air and water, i.e. the timber must be above the fibre saturation point but must not be saturated-this last condition is why living wood is not attacked. The minimum moisture content for growth is about 27%, Sapstaining fungi are resistant to cold and are not killed by severe frost.

The fruit bodies individually are very small-typically 1/10 – 1/4 mm diameter and appear as a matt on

the surface. Sapstain has no significant effect on the compression and bending strength of wood, but

the toughness (resistance to shock) is lowered in severe attack up to 30%. Sapstained timber can therefore be used for most purposes, but not where exceptional toughness is required, e.g. in aircraft.

Stained wood absorbs water and oil-borne preservatives much more readily than unstained.

Soft rot is caused by micro-fungi differing from the true timber rots.

Wood attacked by soft rots usually retains its shape, and when dry, may appear normal, although if

splintered with a knife will break through with brash fracture. When moist, attacked wood is very soft and usually discoloured.

Decay may penetrate deeply, although since much soft rot occurs when timber is very wet, decay tends to be on the surface only, presumably due to lack of oxygen at depth.

Soft rots are very widespread, but under normal conditions their action is very slow, so that where attack by wet or dry rot can occur, they are of minor importance.

Soft rots can, however, tolerate a wider range of conditions than wet or dry rot, and will attack wood that is too wet or too dry for other wood-rotting fungi. They are a very serious hazard in cooling towers.

Soft rots are often responsible for the eventual decay of woods durable to Basidiomycetes, and also

account for much of the eventual preservative failure.

The presence of soft rots also has an important bearing on the establishment of wood borers, most especially marine borers.

It frequently happens that the presence of Dry Rot in a building is not suspected until a floorboard or

other timber collapses. Sometimes the sudden appearance of a growing fruit body makes the fact obvious.

Attacks usually start at or below ground-floor level and may continue up the whole height of the building.

Where an attack is suspected, these indications should be looked for:

•   A damp, musty smell, which at times becomes offensive.

•   Warping of skirting and floorboards, usually curving outwards.

•   The development of deep surface cracks, particularly across the grain.

•   The presence of a fine rusty red powder-the spores of the fungus.

Timber which has been attacked can easily be penetrated by a knife or sharp tool; when struck it does not ring like sound timber.

Where, as sometimes happens, only a fruit body is visible, it must always be remembered that a

considerable amount of wood must have already been consumed before it could have been produced. Fruit bodies often appear on brickwork some distance away from the seat of the attack, and in such cases the building must be opened up until this and the full extent of attack is traced. In searching for the source of an attack of Dry Rot, two essential points must always be remembered-where does the moisture come from, and where is the wood that has been feeding the fungus?

Special attention should be paid to external walls, which may be admitting damp. Defects in rainwater pipes and gullies should be looked for and airbricks examined in case they may have been stopped up. Inside the house, sinks, bathrooms, and lavatories and any places where there might be plumbing defects, are possible causes of the trouble. If it is found that Dry Rot is present, it is essential to trace the source of damp that has been responsible for the outbreak, and everything possible should be done to make the building dry. Unless this is done, there will always be the risk of a renewed outbreak occurring. Always open up woodwork freely, since the fungus may have spread behind plaster and through walls into rooms beyond that in which the attack originated. It is essential that the extreme limits of the attack should be determined. This can only be done with even tolerable certainty if all wood is laid bare, and brickwork behind plaster examined for some three feet in all directions from the known extremities of attack.

Before commencing any form of treatment open up all timbers and examine behind plaster until the full extent of attack has been ascertained.

1. Locate and cure the cause of damp; defective gulleys and drains, broken roof tiles, bridged or defective   

   damp-proof courses, blocked airbricks, leaking gutters, radiators, rainwater pipes and defective 

   plumbing may be the cause and should be rectified.

2. Cut away and burn all infected timber and some 18 inches (0·5 metres) of apparently sound timber 

    since this may have fungus strands in it.

3. Remove all dust, dirt, old shavings and sawdust, acoustic or thermal insulating material which may 

    contain strands of the fungus.

4. Ensure ventilation to hollow floors, clear airbricks and ventilators which have been stopped up. Ensure 

    that these are sufficient in size, number and properly placed to allow adequate ventilation. Install new 

    airbricks if necessary. Sleeper walls should be honeycombed to allow through passage of air.

5. Earth and rubbish which has risen above the damp course on the outer walls or sleepers should be 

    removed. (Building Research Station Digest No. 18 recommends airbricks with a minimum open area of 

    I½ square inches per foot run (30 square centimetres per metre) of wall and a clear depth of 6 inches 

    (0· 15 metres) between the bottom of the floor joists and the site covering.)

6. Strip off any plaster which contains fungal strands or behind which fungus is growing to at least 2 feet 

    (60 cm) beyond the observed limit of growth. Clean down all brickwork or masonry which is near 

    infected timber or which has fungus strands growing on it.

Bore holes sloping downwards into the walls at 9 inch (25 cm) centres I foot (30 cm) above and around the periphery of the infected area to within 2 inches (5 cm) of the far side of the wall (for walls over 9 inches (25 cm) thick, bore from both sides). Needs to be treated with a Dry Rot Killer for Brickwork and Masonry into these holes so as to thoroughly irrigate the wall. Within the infected area apply the treatment to both sides of the wall with a brush or spray. With severe outbreaks drill holes at 2-3 foot (60-90 cm) centres over the whole of the infected area and irrigate thoroughly with a Dry Rot Killer for Brickwork and Masonry treatment. Spray solid concrete floors, grounds and subsoil freely with Dry Rot Killer for Brickwork and Masonry treatment.

7. All sound timber, skirtings and panelling in the vicinity must be treated with three flowing brush or 

    spray coats of a Wood Preserver on all surfaces. Paint, varnish or other surface coatings must be 

    removed before applying the Wood Preserver. If any of the sound wood was affected by damp, then it 

    must be allowed to dry before applying the Wood Preserver.

8. All new wood used for replacement must be well seasoned and must be treated with a Wood Preserver. 

    Treatment must be with three flowing brush or spray coats to all surfaces and with the end grain 

    dipped in a bucket or by total immersion for 10 minutes. In brush or spray application second and third 

    coats must be applied before the previous coat is dry, or by immersion for 10 minutes.

It is important to see that every side of the timber is thoroughly treated. It is useless to apply a preservative to one face only; this will not protect the wood from attack. It is for this reason that immersion is preferred, where possible, since this auto-matically ensures that every part of the wood receives complete treatment. Wherever possible, treatment should be of fully worked timbers; if this is not possible, any fresh surfaces exposed by cutting, drilling, etc., must be brush treated with Preserver before final installation.

Several fungi, with different characteristics, cause wet rot; identification, as a group, depends on the

absence of any of the characteristics of the True Dry Rot Merulius lacrymans, i.e. no massive white or grey surface mycelial growth and no flat pancake-like fruiting bodies with white edges and a brickred centre.

The characteristics of the individual fungi causing Wet Rot are shown above.

The majority of wet rot is, however, caused by the Cellar Fungus-Coniophora cerebella. This fungus darkens the wood considerably and cracks it along the grain. Cracks across the grain are usually fine or absent, and only rarely are as deep as those in the case of True Dry Rot. Cellar Fungus may be distinguished from Dry Rot in that surface growth is often totally absent, and when present consists of thin dark brown, almost black strands, not in any way resembling the thick grey strands or matt of Dry Rot. Attack may often be internal with little signs of it on the surface. The fruiting body is an irregular thin olive-green skin, turning a dull olive-brown when old.

If it is quite certain that decay has been caused by a wet rot, it is unnecessary to sterilize brickwork as for Dry Rot.

The source of dampness must be located and eliminated. When this has been done and the site dried out, the fungus will cease activity, although all decayed and infected wood should be cut out and all replacement and surrounding, in situ, sound timbers treated with Wood Preservers.

Occasionally a rot outbreak is discovered in its early stages, before the timber is seriously penetrated

or weakened. It is then often possible to stamp it out by freely applying Wood Preservers to the timber. After such a treatment, a careful watch should be kept in case eradication was not complete. Where wood is used in the open, the question of the eradication of the fungus hardly arises, as in the case of rot outbreaks in buildings. Fences and out-buildings are seldom kept under close observation. In consequence, the wood usually becomes completely rotten before the attack is noticed. It is essential therefore that all wood used in the open should be adequately protected by a wood preservative before it is used.

The presence of sapstain is readily recognized by the blue dis-coloration in the timber. Sapstain cannot be eradicated once it is in timber, but all spread and activity within a piece of timber will cease when it becomes seasoned.

Sapstain can be prevented by dipping unseasoned wood in a suitable grade of Treatment.

Bacteria seldom, if ever, cause failure of wood but when wood is used in damp situations, such as in

ground contact, it is soon colonized by bacteria. The precise effect of this colonization is not yet understood but may well form part of the cycle of events-attack of cell contents by micro-fungi and of cell walls by staining and soft rot fungi which if it is now recognized precedes the ultimate destruction by wood-rotting Basidio-mycete fungi in such situations.

When green wood is kept damp for a Jong period, as is com-mon practice in some timber-producing

countries where felling and extraction is seasonable and green wood must be stored prior to conversion and seasoning, bacteria will also colonize the wood and cause breakdown of parts of the wood structure, particularly in the rays.

While such attack has no visible effect on the wood and does not affect its strength, it does increase

substantially the ease with which it absorbs liquid-either water or preservative. Wood so attacked will therefore require a much longer drying period after treatment with preservative.