ON THE GRADUAL RISE AND DEVELOPMENT OF DRY ROT.
The opinion generally received has drawn a line of discrimination between
the decay accompanied by a vegetable spreading on the surface of the
timber, and that which is effected by an animal existing within it,
which decay is frequently denominated the worm in timber; but as each is
equally entitled to the dreaded appellation, they might more justly be
distinguished as the animal and vegetable rot.
The dry rot in timber derives its name from the effect produced, and
not from the cause: it is so called in opposition to the wet rot, which
is properly denominated, as this exists only in damp situations, and is
applied to the decomposition which takes place in timber containing sap,
and exposed to moisture: but although the dry rot is usually generated
in moisture, in some cases it will flourish independent of extraneous
humidity. Dry rot differs from wet rot in this respect, that the former
takes place only when the wood is dead, whereas the latter may begin when
the tree is standing.
Wet rots are composed of porous fibre running from the rot into the
trunk of the tree. This rot is of a brown colour, and has an offensive
smell. The evil is often found with white spots, the latter of watery
substance: when it has yellow flames, it is very dangerous.
A large quantity of the vegetable kingdom consists of plants differing
totally from the flowering plants in general structure, having no
flowers and producing no seed properly so called, but propagating by
means of minute cellular bodies, called _spores_. These highly organized
vegetables are known to botanists as _Cryptogamia_. Fungi are plants in
which the fructifying organs are so minute, that without the aid of a
powerful microscope they cannot be detected. To the naked eye, the fine
dust ejected from the plant is the only token of reproduction; this dust,
however, is not truly seed, for the word seed supposes the existence
of an embryo, and there is no such thing in the reproductive bodies of
fungi. The correct terms are _spores_, when the seeds are not in a case;
_sporidia_ when enclosed in cases. The spores or sporidia are placed
in or upon the receptacle, which is of very various forms and kinds,
but how different soever these may be, it is the essential part of the
fungus, and in many cases constitutes the entire plant. That portion of
the receptacle in which the reproductive bodies are imbedded is called
the _hymenium_: it is either external, as in the Agaric, where it forms
gills; or included, as in the puff-balls. The _pileus_ of fungi is the
entire head of the plant, not a mere head covering.
Some naturalists have insisted upon the spontaneous production of fungi,
while others maintain that they are produced by seed, which is taken
up and supported in the air until a soil proper for its nourishment is
presented, on which being deposited it springs up of various appearances
according to the principle of the seed, and the nature of the recipient.
It is extremely difficult to give a logical definition of what
constitutes a fungus. It is not always easy with a cursory observation
under the microscope, to determine whether some appearances are produced
by fungi, insects, or organic disease; experience is the safest guide,
and until we acquire that we shall occasionally fail.
In the ‘Index Fungorum Britannicorum,’ 2479 species of British fungi are
enumerated: any detailed account of the arrangement of this extensive
family of plants, or of the character of even its principal sections
would be impossible within the limits of this volume; all that can be
attempted will be a general description of the fungi causing dry rot.
If dry rot shows itself in a damp closet or pantry, the inside of
the china or delf lying there will be coated with a mould, or a fine
powder like brick-dust. This excessively fine powder is no other than
unaccountable myriads of the reproductive spores or _seeds_ of the
fungus; they are red in colour, and are produced on the surface of the
fungus in millions. Certain privileged cells on the face of the fungus
are furnished each with four minute points at their apex, each four
bearing a single brick-red, egg-shaped spore; so that the fruit is spread
over the surface of the fungus in groups of fours. To see the form of
these spores the highest powers of the microscope are required, and then
they can only be viewed as transparent objects. If these excessively
minute bodies be allowed to fall on wet flannel, damp blotting-paper, or
wet wood, they immediately germinate and proceed to reproduce the parent
fungus. The red skin of the spores cracks at both ends, and fine mycelial
filaments are sent out: this is the “mould,” spawn, or mycelium from
which the new fungus (under favourable conditions of continued moisture)
appears.
It matters little where we go: everywhere we are surrounded with life.
The air is crowded with birds and insects; the waters are peopled with
innumerable forms, and even the rocks are blackened with countless
mussels and barnacles. If we pluck a flower, in its bosom we see many a
charming insect. If we pick up a fallen leaf, there is probably the trace
of an insect larvæ hidden in its tissue. The drop of dew upon this leaf
will probably contain its animals, visible under the microscope. The
very mould which covers our cheese, our bread, our jam, or our ink, and
disfigures our damp walls, is nothing but a collection of plants.
The starting point of life is a single cell-that is to say a microscopic
sac filled with liquid and granules, and having within it a nucleus,
or smaller sac. From this starting point of a single cell, this is the
course taken: the cell divides itself into two, the two become four, the
four eight, and so on, till a mass of cells is formed.
The researches of Pasteur show that atmospheric dust is filled with
minute germs of various species of animals and plants, ready to develop
as soon as they fall into a congenial locality. He concludes that all
fermentation is caused by the germination of such infinitesimal spores.
That they elude observation does not seem strange, when we consider that
some infusoria are only ⅟240000 of an inch in length.
It is ascertained that fungi produce seed which contains the properties
of germination; and that vegetable corruption is suited to effect it.
When we contemplate the fineness and volatility of the germs, the
hypothesis will not appear unreasonable that they are conveyed by the
rains into the earth, and are absorbed by vegetables; that with the
sap they are disseminated throughout the whole body, and begin to
germinate as soon as the vegetable has proceeded to corruption. Whatever,
therefore, may be the appearance or situation of the fungus producing the
dry rot, or from whatever substance it originates, that substance must be
in a corrupt state.
Fungi result from, or are attendant on, vegetable corruption, assisted
by an adequate proportion of heat and moisture. The sap, or principle
of vegetation, brought into activity, is, according to the ‘Quarterly
Review,’ No. 15, the cause of dry rot, in as far as it is favourable
to the growth of fungi, as it would seem to be when in a state of
fermentation.
Vegetable corruption invariably presupposes fermentation.
Fermentation is a state of vegetable matter, the component parts of which
have acquired sufficient force to produce an intestinal motion, by which
the earthy saline, the oily and aqueous particles therein contained,
exert their several peculiar attractive and repulsive powers, forming new
combinations, which at first change, and at length altogether destroy
the texture of the substance they formerly composed.
There are two things essential towards creating and supporting the
intestinal motion, namely, heat and humidity; for without heat, the air,
which is supposed to be the cohesive principle of all bodies, cannot be
so rarefied as to resume its elasticity; and without humidity there can
be no intestinal motion.
According to Baron Liebig, the decay of wood takes place in the three
following modes:--First, oxygen in the atmosphere combines with the
hydrogen in the fibre, and the oxygen unites with the portion of carbon
of the fibre, and evaporates as carbonic acid: this process is called
decomposition. Second, we have to notice the actual decay of wood which
takes place when it is brought in contact with rotting substances; and
the third process is called putrefaction. This is stated by Liebig to
arise from the inner decomposition of the wood in itself: it loses its
carbon, forms carbonic acid gas, and the fibre, under the influence of
the latter, is changed into white dust.
The fungus occasioning the dry rot is of various appearances, which
differ according to the situation in which it exists. In the earth, it
is fibrous and perfectly white, ramifying in the form of roots; passing
through substances from the external surface, it somewhat differs from
that form; here it separates into innumerable small branches.
Mr. McWilliam observes, “If the fungi proceed from the slime in the
fissures of the earth, they are generally very ramous, having round
fibres shooting in every direction. If they arise from the roots of
trees, their first appearance is something like hoar frost; but they soon
assume the mushroom shape.”
Hence it appears that we frequently build on spots of ground which
contain the fundamental principle of the disease, and thus we are
sometimes foiled in our endeavours to destroy the fungus by the admission
of air. In this case the disease may be encouraged by the application of
air as a remedy. When workmen are employed in buildings which contain dry
rot, and when they are working on ground which contains the symptoms of
this disease, their health is often affected. A London builder informs
us, that a few years since, while building some houses at Hampstead
his men were never well: he afterwards ascertained that the ground was
affected with rot, and that within one year after the house was erected,
all the basement floor was in a state of premature decay. Sir Robert
Smirke, architect, remarked in 1835, that he had noticed “there are
certain situations in which dry rot prevails remarkably.”
The fungus protruded in a very damp situation is fibrous, of moderate
thickness, feels fleshy. From the spot whence it arises it extends
equally around, wholly covering the area of a circle. This form would
possibly continue in whatever situation it might vegetate, if the air had
no motion, and every part of the substance on which it grew were equally
supplied with a matter proper to encourage the expansion. The surface of
this fungus is pursed, and of various colours, the centre is of a dusky
brown, mixed with green, graduated into a red, which degenerates into
yellow, and terminates in white.
One of the most formidable of the tribe of fungi is the _Merulius
lachrymans_ (often called _the_ Dry Rot) of which the following
description is given by Dr. Greville: “Whole plant generally resupinate,
soft, tender, at first very light, cottony, and white. When the veins
appear, they are of a fine yellow, orange, or reddish brown, forming
irregular folds, most frequently so arranged as to have the appearance
of pores, but never anything like tubes, _and distilling, when perfect,
drops of water_.” Hence the term _lachrymans_, from _lacrymo_, Lat., I
weep: the _Merulius lachrymans_ is often dripping with moisture, as if
weeping in regret for the havoc it has made. In the genus _Merulius_,
the texture is soft and waxy, and the hymenium is disposed in porous or
wavy toothed folds. Berkeley, in his ‘Fungology,’ gives the following
description, which is similar to Dr. Greville’s: “Large, fleshy but
spongy, moist, ferruginous yellow, arachnoid and velvety beneath;
margin tomentose, white; folds ample, porous, and gyroso-dentate.” The
_Merulius_ is found in cellars and hollow trees, sometimes several feet
in width, and is the main cause of dry rot.
Another formidable fungi, which attacks oak in ships, is the _Polyporus
hybridus_ (the dry rot of our oak-built vessels). It is thus described by
Berkeley: “White, mycelium thick, forming a dense membrane, or creeping
branched strings, hymenium breaking up into areæ, pores long, slender,
minute.”
From the slow progress dry rot makes in damp situations, it appears
that excessive damps are inimical to the fungus, for its growth is more
rapid in proportion as the situation is less damp, until arrived at that
certain degree of moisture which is suited both to its production and
vegetation. When further extended to dry situations, its effects are
considerably more destructive to the timber on which it subsists: here
it is very fibrous, and in part covered with a light brown membrane,
perfectly soft and smooth. It is often of much greater magnitude,
projecting from the timber in a white spongeous excrescence, on the
surfaces of which a profuse humidity is frequently observed: at other
times, it consists only of a fibrous and thin-coated web irregularly on
the surface of the wood. Excrescences of a fungiform appearance are often
protruded amidst those already described, and are evidences of a very
corrupt matter peculiar to the spots whence they spring. According to the
situation and matter in which they are produced, they are dry and tough,
or wet, soft, and fleshy, sometimes arising in several fungiforms, each
above the other, without any distinction of stem; and when the matter
is differently corrupted, it not unfrequently generates the small acrid
mushroom.
Mr. McWilliam observes, “The fungi arising from oak timbers are generally
in clusters of from three to ten or twelve; while those from fir timber
are mostly in single plants: and these will continue to succeed each
other until the wood is quite exhausted.”
Damp is not only a cause of decay, but is essential to it; while, on the
other hand, absolute wet, especially at a low temperature, prevents it.
In ships this has been particularly remarked, for that part of the hold
of a ship which is constantly washed by the bilge-water is never affected
with dry rot. Neither is that side of the planking of a ship’s bottom
which is next the water found in a state of decay, even when the inside
is quite rotten, unless the rot has penetrated quite through the inside.
It matters little whether wet is applied to timber before or after
the erection of a building. Timber cannot resist the effect of what
must arise in either case; viz. heat and moisture, producing putrid
fermentation; for instance, in basement stories with damp under them,
dry timber is but little better than wet, for if it is dry it will soon
be wet; decay will only be delayed so long as the timbers are absorbing
sufficient moisture, therefore every situation that admits moisture is
the destruction of timber.
In a constancy and equality of temperature timber will endure for ages.
Sir Christopher Wren, in his letter to the Bishop of Rochester, inserted
in Wadman’s ‘History of Westminster Abbey,’ notices “That Venice and
Amsterdam being both founded on wooden piles immersed in water, would
fall if the constancy of the situation of those piles in the same element
and temperature did not prevent the timber from rotting.” Nothing is more
destructive to woodwork than _partial leaks_, for if it be kept _always
wet_ or _always dry_, its duration is of long continuance. It is recorded
that a pile was drawn up sound from a bridge on the Danube, that parted
the Austrian and Turkish dominions, which had been under water 1500 years.
The writer of an article on the decay of wood, in the ‘Encyclopædia
Britannica,’ 1855, observes, “If a post of wood be driven into the
ground, the decay will commence at the surface of the ground; if driven
into the earth through water, the decay will commence at the surface of
the water; if used as a beam let into a damp wall, rot will commence just
where the wood enters the wall.”
Humboldt observes in his ‘Cosmos,’ with reference to damp and damp rooms,
that anyone can ascertain whether a room is damp or not, by placing a
weighed quantity of fresh lime in an open vessel in the room, and leaving
it there for twenty-four hours, carefully closing the windows and doors.
At the end of the twenty-four hours the lime should be reweighed, and if
the increase exceeds one per cent. of the original weight, it is not safe
to live in the room.
Decay of timber will arise from the effects of continued dryness or
continued wetness, under certain conditions; or it may also arise from
the effect of alternate dryness and moisture, or continued moisture with
heat.
At one time dry rot appears to have made great havoc amongst the wooden
ships of the British Navy. In the Memoirs of Pepys, who was Secretary to
the Admiralty during the reigns of Charles II. and James II., reference
is made to a Commission which was appointed to inquire into the state of
the navy, and from which it appears that thirty ships, called new ships,
“for want of proper care and attention, had toadstools growing in their
holds as big as one’s fists, and were in so complete a state of decay,
that some of the planks had dropped from their sides.”
In the ‘European Magazine’ for December, 1811, it is stated that, “about
1798, there was, at Woolwich, a ship in so bad a state that the deck
sunk with a man’s weight, and the orange and brown coloured fungi were
hanging, in the shape of inverted cones, from deck to deck.”
Mr. William Chapman, in his ‘Preservation of Timber from Premature
Decay,’ &c., gives several instances of the rapid decay of the ships
of the Royal Navy, about the commencement of the present century. He
mentions three ships of 74 guns each, decayed in five years; three of
74 guns each, decayed in seven years; and one of 100 guns, decayed in
six years. Mr. Pering, also, in his ‘Brief Enquiry into the Causes of
Premature Decay,’ &c., says that ships of war are useless in five or
six years; and he estimates the average duration to be eight years, and
that the cost of the hull alone of a three-decker was nearly 100,000_l._
Mr. Pering was formerly at the dockyard, Plymouth, and therefore a good
authority, if he availed himself of the opportunities of studying the
subject. He has stated that he has seen fungi growing so strong betwixt
the timbers in a man-of-war, as to force a plank from the ship’s side
half an inch.
No doubt a great deal of this decay was attributable to the use of
unseasoned timber, and defective ventilation; but there is too much
reason to believe that it was principally owing to the introduction
of an inferior species of oak (_Quercus sessiliflora_) into the naval
dockyards, where, we imagine, the distinction was not even suspected. The
true old English oak (_Quercus robur_) affords a close-grained, firm,
solid timber, rarely subject to rot; the other is more loose and sappy,
very liable to rot, and not half so durable.
One cause of the decay of wood in ships is the use of wooden treenails.
A treenail is a piece of cleft wood (made round), from 1 foot to 3
feet 6 inches in length and 1½ inch in diameter. As the treenails are
also made to drive easy, they never fill the holes they are driven
into; consequently, if ever it admits water at the outer end, which,
from shrinking, it is liable to do, that water immediately gets into
the middle of the plank, and thereby forms a natural vehicle for the
conveyance of water. The treenail is also the second thing which decays
in a ship, the first, generally, being the oakum. Should any part of
the plank or timbers of a ship be in an incipient state of decay, and a
treenail come in contact with it, the decay immediately increases, while
every treenail shares the same fate, and the natural consequence is, the
ship is soon left without a fastening. Treenails in a warm country are
sure to shrink and admit water.
Mr. Fincham, formerly Principal Builder in Her Majesty’s dockyard,
Chatham, considers that the destruction of timber by the decay commonly
known as dry rot, cannot occur unless air, (?) moisture, and heat are
all present, and that the entire exclusion of any of the three stays the
mischief. By way of experiment, he bored a hole in one of the timbers of
an old ship built of oak, whose wood was at the time perfectly sound;
the admission of air, the third element, to the central part of the wood
(the two others being to a certain degree present) caused the hole to be
filled up in the course of twenty-four hours with mouldiness, which very
speedily became so compact as to admit of being withdrawn like a stick.
The confinement of timber under most circumstances is attended with the
worst consequences, yet a partial ventilation tends to fan the flame of
decay.
The admission of air has long been considered the only means of
destroying the fungus, but as it has frequently proved ineffectual, it
must not be always taken as a certain remedy. If dry air be properly
admitted, in a quantity adequate to absorb the moisture, it will
necessarily exhaust and destroy the fungus; but care should be taken lest
the air should be conveyed into other parts of the building, for, after
disengaging itself from the fungus over which it has passed, it carries
with it innumerable seeds of the disease, and destroys everything which
offers a bar to its progress. Air, in passing through damps, will partake
of their humidity; it therefore soon becomes inadequate to the task for
which it is designed. Owing to this circumstance, air has been frequently
admitted into the affected parts of a building without any ultimate
success; too often, instead of injuring the fungus, it has considerably
assisted its vegetation, and infected with the disease other parts of the
building, which would otherwise probably have remained without injury.
The timber, which is in a state of decomposition by an intestinal decay,
is little affected by the application of air, as this cannot penetrate
the surrounding spongeous rottenness which generally forms the exterior
of such timber, and protects the action which the humid particles have
acquired in the exterior: as the extent and progress of the disease
is therefore necessarily concealed, it is difficult to ascertain
correctly the effect produced by the admission of dry air. Under these
circumstances of necessity and danger, it will require considerable
skill to effect the purpose without increasing the disease, and, as each
case has its own peculiar characteristics, it is necessary before one
attempts to admit air as a remedy, to previously estimate the destructive
consequences which may result from so doing, and ascertain whether it
will be injurious or beneficial to the building. The joists of the houses
built by our ancestors last almost for ever, because they are in contact
with an air which is continually changing. Now, on the contrary, we
foolishly enclose them between a ceiling of plaster (always very damp to
begin with) and a floor; they frequently decay, and then cause the most
serious disasters, of which it is impossible to be forewarned.
Damp, combined with warmth, is as a destroying agent, still more active
than simple damp alone--the heat being understood as insufficient to
carry off the moisture by evaporation; and the higher the temperature
with a corresponding degree of moisture, the more rapid the decay. If
the temperature to which wood is exposed, whilst any sap remains in
it, is too elevated, the vegetable fluids ferment; the tenacity is
diminished, and when the action is carried to its full extent, the wood
quickly becomes affected by the dry rot. Exposure to the atmosphere in
positions where rain can lodge in quantity, contact with the ground, and
application in damp situations deprived of air, will render wood liable
to the wet rot; and however well seasoned it may have been previously
to being brought within the influence of any of these causes, it will
infallibly suffer. Air should therefore have free access to the wood in
every direction:
… “for without in the wall of the house he made narrowed rests
round about, that the beams should not be fastened in the walls
of the house.”--1 Kings vi. 6.
Rondelet says, “The woodwork of the church of St. Paul, outside the city
walls, which was destroyed by fire in 1823, was erected as far back as
the fifth century.” Although the atmosphere surrounding the framework
was often at once warm and damp, yet it was never stagnant. It should be
remembered that 500 people in a church during two hours give off fifteen
gallons of water into the air, which, if not carried away, saturates
everything in the building after it has been breathed over and over
again in conjunction with the impurities it contains collected from each
individual.
Fever, scrofula, and consumption arise in many instances from defective
ventilation.
The signs of decay in timber are, as has been stated, fungi. Some of them
now and then are microscopic, and owe their existence to the sporules
deposited on the surface; while fermentation, generated by prolonged
contact with warm, damp, and stagnant air, is as a soil where seeds sow
and nourish themselves.
Mr. McWilliam, in his work on dry rot, states that if the temperature
be very low or very high, the effects are the same with respect to the
growth of fungi. At 80° dry rot will proceed rapidly, at 90° its progress
is more slow; at 100° it is slower still, and from 110° to 120° it will
in general be arrested. It will proceed fast at 50°; it may be generated
at 40°; its progress will be slow at 36°; and is arrested at 32°, yet it
will return if the temperature is raised to 50°.
Dry rot externally first makes its appearance as a mildew, or rather
a delicate white vegetation, that looks like such. The next step is a
collecting together of the fibres of the vegetation into a more decided
form, somewhat like hoar frost; after which it speedily assumes the
leathery, compact character of the fungus, forming into leaves, spreading
rapidly in all directions, and over all materials, and frequently
ascending the walls to a considerable height, the colour variable--white,
greyish white, and violet, light or decided brown, &c.
In the section of a piece of wood attacked by dry rot a microscope
reveals minute white threads spreading and ramifying throughout its
substance; these interlace and become matted together into a white
cottony texture, resembling lint, which effuses itself over the surface
of the timber; then in the centre of each considerable mass a gelatinous
substance forms, which becomes gradually of a yellow, tawny hue, and a
wrinkled, sinuated porous consistence, shedding a red powder (the spores)
upon a white down; this is the resupinate pileus, the hymenium being
upwards, of _Merulius lachrymans_, in its perfect and matured state. Long
before it attains to this, the whole interior of the wood on which it
is situated has perished; the sap vessels being gradually filled by the
cottony filaments of the fungus; no sooner do these appear externally
than examination proves that the apparently solid beam may be crumbled
to dust between the fingers; tenacity and weight are annihilated.
Dr. Haller says that seven parts in eight of a fungus in full vegetation
are found by analysis to be completely aqueous.
The strength of fungi is proportionate to the strength of the timber the
cohesive powers and nutritive juices of which they absorb; and according
to the food they receive so they are varied and modified in different
ways, and are not always alike. Different stages of corruption produce
food of different qualities, and hence many of the different appearances
of fungi. One takes the process of corruption up where another leaves it
off, and carries it forward and farther forward to positive putrefaction.
The forms which fungi assume are extremely diversified; in some instances
we have a distinct stem supporting a cap, and looking somewhat like a
parasol; in others the stem is entirely absent, and the cap is attached
either by its margin, and is said to be _dimidiate_, or by its back,
or that which is more commonly its upper surface, when it is called
_resupinate_. In some species the form is that of a cup, in others of
a goblet, a saucer, an ear, a bird’s nest, a horn, a bunch of coral, a
ball, a button, a rosette, a lump of jelly, or a piece of velvet.
Decomposition takes place without fungus where the timber and the
situation are always moist, as in a close-boarded kitchen floor, where
it is always dry, or very nearly so, and where it is alternately wet
and dry, cold and hot. When the decomposition is affected with very
little moisture, and no fungus, the admission of air will generally
prevent further contamination; but where there is abundance of moisture,
rottenness, and fungus, a small quantity of air will hasten the
destruction of the building.
In timber which has been only superficially seasoned this disease is
produced internally, and has been known to convert the entire substance
of a beam, excepting only the external inch or two of thickness to
which the seasoning had penetrated, into a fine, white, and threadlike
vegetation, uniting in a thick fungous coat at the ends, the semblance
being that of a perfectly sound beam. In this internal rot a spongy
fungous substance is formed between the fibres. This has often been
observed in large girders of yellow fir, which have appeared sound on
the outside, but by removing some of the binding joists have been found
completely rotten at the heart. An instance of this kind occurred at
Kenwood (the seat of the Earl of Mansfield) in 1815. Major Jones, R.E.,
states that on one occasion he was called upon to report on the state of
a building in Malta; that the timbers had every external appearance of
being sound, but on being bored with an auger they were found internally
in a total state of decay. It is on this account that the practice of
sawing and bolting beams is recommended, for when timber is large enough
to be laid open in the centre this part is laid open to season; so that
when a tree is large enough to be cut through to make two or more beams,
decomposition is impeded.
The first symptoms of rottenness in timber are swelling, discoloration,
and mouldiness, accompanied with a musty smell; in its greater advance
the fibres are found to shrink lengthways and break, presenting many deep
fissures across the wood; the fibres crumble readily to a fine snuff-like
powder, but retain, when undisturbed, much of their natural appearance.
In whatever way boughs are removed from trees, the effect of their
removal is, however, very frequently to produce a rotting of the inner
wood, which indicates itself externally by a sudden abnormal swelling of
the trunk a little above the root; sometimes the trunk becomes hollow at
the part affected, and this particular description of rot will almost
invariably be found to exist in those trees whose roots are much exposed.
The rot itself is either of a red, black, or white colour in the timber
when felled, and when either of the two last-named colours prevail, it
will be found that the decay does not extend very far into the tree;
but if, on the contrary, the colour of the parts most visibly affected
should be decidedly red, the wood should be rejected for any building
purposes. Sometimes small brown spots, indicative of a commencement of
decay, may be observed near the butt or root end of trees, and though
they do not appear to be connected with any serious immediate danger to
the durability of the wood, it is advisable to employ the material so
affected only in positions where it would not be confined in anything
like a close, damp atmosphere.
Great hesitation may be admitted as to the use of timber which presents
large bands of what are supposed to be indefinitely-marked annual
growth, because the existence of zones of wood so affected may be
considered to indicate that the tree was not in a healthy state when they
were formed, and that the wood then secreted lacked some of the elements
required for its durability, upon being subsequently exposed to the
ordinary causes of decay.
In many cases when timber trees are cut down and converted for use, it
is found that at the junction of some of the minor branches with the
main stem, the roots, as it were, of the branches traverse the surface
wood in the form of knots, and that they often assume a commencement of
decay, which in the course of time will extend to the wood around them.
This decay seems to have arisen in the majority of cases from the sudden
disruption of the branch close to its roots, with an irregular fracture,
and with such depressions below the surface as to allow the sap to
accumulate, or atmospheric moisture to lodge in them. A decomposition of
the sap takes place--in fact, a wound is made in the tree-and what are
called “druxy knots” are thus formed, which have a contagious action on
the healthy wood near them.
There is this particular danger about the dry rot; viz. that the germs
of the fungi producing it are carried easily, and in all directions, in
a building wherein it once displays itself, without necessity for actual
contact between the affected or the sound wood; whereas the communication
of the disease resulting from the putrefactive fermentation, or the wet
rot, only takes place by actual contact.
[Illustration: _Timber Beams,--rotten at the heart._]
Before dry rot has time to destroy the principal timbers in a building,
it penetrates behind the skirtings, dadoes, and wainscotings, drawing
in the edges of the boards, and splitting them both horizontally and
vertically. When the fungus is taken off, they exhibit an appearance
similar both in back and front to wood which has been charred; a light
pressure with the hand will break them asunder, even though affected with
the rot but a short time; and in taking down the wainscot, the fibrous
and thin-coated fungus will generally be seen closely attached to the
decayed wood. In timber of moderate length the fungus becomes larger and
more destructive, in consequence of the matter congenial to its growth
affording a more plentiful supply.
It is a great characteristic of fungi in general that they are very
rapid in growth, and rapid in decay. In a night a puff-ball will grow
prodigiously, and in the same short period a mass of paste may be covered
with mould. In a few hours a gelatinous mass of _Reticularia_ will pass
into a bladder of dust, or a _Coprinus_ will be dripping into decay. Many
instances have been recorded of the rapidity of growth in fungi; it may
also be accepted as an axiom that they are in many instances equally as
rapid in decay.
In considering the liability of any particular description of foreign
timber to take the dry rot, attention must be paid to the circumstances
under which it is imported. Sometimes the timber is a long while coming
here, whilst at other times it is imported in a very short period. The
length of time consumed in the voyage has a great deal to do with its
likelihood of taking the rot: it may have a very favourable passage, or
a very wet one, and the ship is frequently, in some degree, affected
with the disease. It perhaps begins in the ship, and it may often be
seen between the timber or deals, when it will impregnate the wood to a
great depth. Whether it is inherent in the timber or not, of this we may
be certain, that where there is a fetid atmosphere it is sure to grow.
Canadian yellow wood pine timber is more subject to rot than Baltic or
Canadian red wood timber, although the latter will sometimes decay in
four or five years. Turpentine is a preventive against dry rot, and
Canadian timber is sometimes largely impregnated with it, especially the
red wood timber; the yellow wood is very subject to dry rot. Very few
cargoes of timber in the log arrive from Canada in which in one part or
other of nearly every log you will not see a beginning of the vegetation
of the rot. Sometimes it will show itself only by a few reddish,
discoloured spots, which, when scratched by the finger nail to the extent
of each spot, it will be seen that the texture of the timber to some
little depth is destroyed, and will be reduced to powder; and on these
spots a white fibre may generally be seen growing. If the timber has been
shipped in a dry condition, and the voyage has been a short one, there
may be a few logs without a spot; but generally speaking very few cargoes
arrive from Canada in which there are many logs of timber not affected.
But if the cargo has been shipped in a wet condition, and the voyage has
been a long one, then a white fibre will be seen growing over nearly
every part of the surface of every log; and in cargoes that have been so
shipped, all the logs of yellow pine, red pine, and of oak, are generally
more or less affected on the surface.
Nearly every deal of yellow pine that has been shipped in Canada in a
wet state, when it arrives here is also covered over with a network of
little white fibres, which are the dry rot in its incipient state. There
is no cargo, even that which is shipped in tolerably dry condition, in
which, upon its arriving here, may not be found some deals, with the
fungus beginning to vegetate on their surface. If they are deals that
have been floated down the rivers of America or Canada, and shipped in a
wet state, on their arrival here they are so covered with this network
of the fungus, that force is often necessary to separate one deal from
another, so strongly does the fungus occasion them to adhere. They grow
together again, as it were, after quitting the ship, while lying in the
barges, before being landed. Accordingly, if a cargo has arrived in a wet
condition, or late in the year, or if the rain falls on the deals before
they are landed, and they are then piled in the way in which Norwegian
and Swedish deals are piled, that is, flatways, in six months time, or
even less, the whole pile of deals become deeply affected with rot; so
that, whenever a flat surface of one deal is upon the flat surface of
another, the rot penetrates to the depth of ⅛ of an inch. Its progress
is then arrested by repiling the deals during very dry weather, and by
sweeping the surface of each deal before it is repiled: but the best way
is to pile the deals in the first instance upon their edges; by which
means the air circulates freely around them, the growth of the fungus
is arrested, and the necessity of repiling them prevented. If the ship
is built of good, sound, and well-seasoned oak, the rot would perhaps
not affect it, but in order to prevent its doing so, the precaution is
usually taken to scrape the surface as soon as the hold is clear of the
cargo of timber. Were the cargo not cleared, and the hold not ventilated,
a ship that was permanently exposed to this fungus would, no doubt, be
affected. It is easy, however, to prevent its extending by washing the
hold with any desiccating solution.
Anyone who wishes to know how timber is occasionally shipped to this
country should read the report of a trial, in the ‘Times,’ 22nd Feb.,
1875 (Harrison _v._ Willis), relative to a cargo of pitch pine shipped
from Sapelo, in the Isthmus of Darien, for Liverpool. This cargo,
however, never arrived at Liverpool: it was lost at sea.
The motto of the Worshipful Company of Shipwrights is, “Within the ark,
safe for ever.” We suggest it should be altered to, “Within the ark
_which is free from dry rot_, safe for ever.”
There are two descriptions of European deals very liable to take the dry
rot; viz. yellow Petersburgh deals, and yellow and white battens, from
Dram, in Norway. When Dram battens, which have been lying a long time in
bond in this country, have not been repiled in time, they have been found
as much affected with the dry rot as many Canadian deals; though this has
not happened in so short a time as has been sufficient to rot Canadian
deals. The fungus growing on the Petersburgh deals and Dram battens
has all the characteristics and effects of dry rot as exhibited in the
Canadian deals, the detection of dry rot being in most cases the same.
It should be remembered that white deal absorbs more water than yellow;
and yellow more water than red; and the quantity of water absorbed by
the white accounts for its more rapid decay in external situations; as
the greater the quantity of water absorbed the quicker is the timber
destroyed. Mr. John Lingard, in his work on timber (1842), states that he
has proved that 4½ oz. of water can be driven off from a small piece of
fir, weighing only 10 oz. when wet, which is nearly half. This timber was
on a saw-pit, and going to be put into a building.
The most general, and the most fatal cause of decay, viz. the wet rot,
has attracted less attention than the more startling, but less common
evils, the dry rot, and the destruction by insects.
Sir Thomas Deane, in 1849, related before the Institution of Civil
Engineers of Ireland, an extraordinary instance of the rapid decay of
timber from rot, which occurred in the church of the Holy Trinity at Cork.
On opening the floors under the pews, a most extraordinary appearance
presented itself. There were flat fungi of immense size and thickness,
some so large as almost to occupy a space equal to the size of a pew,
and from 1 to 3 inches thick. In other places fungi appeared, growing
with the ordinary dry rot, some of an unusual shape, in form like a
convolvulus, with stems of from a quarter to half an inch in diameter.
When first exposed, the whole was of a beautiful buff colour, and emitted
the usual smell of the dry-rot fungus.
During a great part of the time occupied in the repairs of the church,
the weather was very rainy. The arches of the vaults having been turned
before the roof was slated, the rain water saturated the partly decayed
oak beams. The flooring and joists, composed of fresh timber, were laid
on the vaulting before it was dry, coming in contact at the same time
with the old oak timber, which was abundantly supplied with the seeds of
decay, stimulated by moisture, the bad atmosphere of an ill-contrived
burial-place, and afterwards by heat from the stoves constantly in use.
All these circumstances account satisfactorily for the extraordinary and
rapid growth of the fungi.
Many instances might be mentioned of English oak being affected with
dry rot, under particular circumstances. There was a great deal at the
Duke of Devonshire’s, at Chiswick, about 60 years ago. Needy builders,
who work for contract, sometimes use American oak, and call it wainscot:
it is a bad substitute for wainscot, being very liable to warp and to
be affected with dry rot. “I know of one public building,” observed the
late Mr. Henry Warburton, M.P., “in which it has been introduced, and, I
suppose, paid for under that name.”
Another serious instance of the decay of timber from rot occurred some
time since in Old St. Pancras Church, London. When the dry rot made its
appearance, it spread with amazing rapidity. Sometimes in the course of a
night, a fungus of about the consistence of newly-fallen snow, and of a
yellowish-white unwholesome colour, would be found to have spread over a
considerable surface. The fungus was without shape, but in some cases it
rose to a height of 2, 3, or 4 inches above the planks or other surfaces
on which it grew. It could be cut with a knife, leaving a clear edge on
each side, and there did not seem to be any covering or membrane over
the outer or under surface. The smell of those matters was unpleasant,
and seemed like the concentration of the smell which had pervaded the
church for so long a time before; and, in a short time, beams, planks of
flooring, railings, &c., were reduced to rottenness: the colour changed,
and a heavy dark-brown dust fell, and represented the once solid timber.
On making an examination with a view of discovering the cause of the
attack, it was found that in the graveyard, near the church, there were
graves, and several vaults: there were also vaults in the inside of the
church. Most of them were filled, or nearly so, with water, which had run
from the overcrowded graves.
In the interior there were water-logged vaults, and the walls were
saturated with damp. It was also seen that from want of proper spouts
and drains, near the outer walls, the drip from the large pent roof had
fallen into the foundations. In this situation, when the window frames
were properly arranged, a drain dug round and from parts of the church,
and other alterations, which should long before have been made, were
completed, the dry rot vanished, and no more complaints of the foulness
of the air have since been heard.
We could quote many cases of rot which have been caused from the want of
proper drains and spouts. Architects should remember that the feet of
Gothic collar roofs have to bear the whole weight of the roof, and unless
well seasoned, and carefully protected from damp, leaks, &c., premature
decay and dry rot will be sure to occur. It is surprising what injury
leaks from gutters will sometimes do. In 1851, Professor T. L. Donaldson
stated that “a brestsummer of American timber was used some time since
at a house in London: after an expiration of three years cracks began to
appear in the front wall. A friend of mine, an architect, was called in
to find out the cause; and after examining different parts of the house,
was almost giving up his search in despair, when he thought he would have
the shop cornice removed and look at the brestsummer. He then discovered
that some water had been admitted by accident, and penetrating the
brestsummer, had caused it to rot, and crack the wall.”
Dry rot was found in the great dome of the Bank of England, London, as
originally built by Sir Robert Taylor: it also existed in the Society of
Arts building, in the Adelphi, London. It was also found in the domes of
the Panthéon, and Halle-au-Blé, Paris; but we hope there is no dry rot in
the dome of St. Paul’s Cathedral, London, which is constructed entirely
of timber, covered externally with lead.
The decayed state of a barn floor attacked by rot is thus described by
Mr. B. Johnson: “An oak barn floor which had been laid twelve years began
to shake upon the joists, and on examination was found to be quite rotten
in various parts. The planks, 2½ inches in thickness, were nearly eaten
through, except the outsides, which were glossy, and apparently without
blemish. The rotten wood was partly in the state of an impalpable powder,
of a snuff colour; other parts were black, and the rest clearly fungus.
No earth was near the wood.” This oak was probably of the _Quercus
sessiliflora_ species; and there was no ventilation to the floor.
Mr. John Armstrong, carpenter, employed for many years at Windsor Castle,
observed: “I was employed a few years back at a house where I found a
floor rotten. We took it up; it was yellow pine; it was laid in the
damp, but on sleepers, and the sleepers were not rotten: they were of a
different description of wood.” Probably the sleepers were of Baltic red
wood.
Dr. Carpenter relates an instance of the expansive power resulting
from the rapid growth of the soft cellular tissue of fungi. About the
commencement of this century the town of Basingstoke was paved; and not
many months afterwards the pavement was observed to exhibit an unevenness
which could not easily be accounted for. In a short time after, the
mystery was explained, for some of the heaviest stones were completely
lifted out of their beds by the growth of large toadstools beneath them.
One of these stones measured 22 inches by 21 inches, and weighed 83 lb.,
and the resistance afforded by the mortar which held it in its place
would probably be even a greater obstacle than the weight. A similar
incident came under the notice of Mr. M. C. Cooke (the author of ‘British
Fungi’), of a large kitchen hearthstone which was forced up from its bed
by an under-growing fungus, and had to be relaid two or three times,
until at last it reposed in peace, the old bed having been removed
to the depth of 6 inches, and a new foundation laid. A circumstance
recorded by Sir Joseph Banks is still more extraordinary, of a cask of
wine which, having been confined for three years in a cellar, was, at
the termination of that period, found to have leaked from the cask, and
vegetated in the form of immense fungi, which had filled the cellar, and
borne upwards the empty wine cask.
Timber decay in contact with stone is a subject deserving consideration.
This decay is entirely obviated by inserting the wood in an iron shoe,
or by placing a thin piece of iron between the wood and the stone. It is
said that a hard crust is formed on the timber in contact with the iron,
which seems effectually to preserve it; it is, of course, necessary that
a free circulation of air round the ends of the timber be provided. The
most notable instance of timber decay in contact with stone with which we
are acquainted occurred at the coronation of George IV. Westminster Hall
was then fitted up, and they began by laying sleepers of yellow pine. The
coronation was suspended for twelve months, and when the sleepers were
taken up from the floor of Westminster Hall, they were in a rotten state.
Timber in contact with brickwork is in Suffolk and in some parts of
England covered with sheet lead to preserve it from the effects of the
damp mortar. Fungi will arise in mortar, if made with road-drift, and
water from stagnant ponds, &c., and it may be traced through the mortar
joints, and will thus appear on both sides of a wall. Mortar composed of
unwashed sand will generate fungi; sea sand, even if washed, should never
be used. It is considered that the system of grouting contributes to the
early decay of timber; wood bond timber for walls has been consequently
replaced by hoop iron bond. In Manchester wood bond is frequently used,
and is said to answer well, but the high temperature of the buildings may
be a preventive against the decay of timber, as the walls are soon dried.
The practice is a bad one.
When timber used as posts inserted in the ground is placed in the
inverted position to that in which it stood when growing, it is said
to be very much more durable than if placed in its natural or growing
position. This is easily accounted for in the valves of the sap vessels
of the growing timber opening upwards; but when that position is
inverted, the valves of the sap vessels become reversed in their action;
and, therefore, when timber is used as posts inserted in the ground, the
valves being so reversed prevent the ascent of moisture from the soil in
the wood. Mr. W. Howe relates an experiment made to test the comparative
durability of posts set as they grew. He says, “Sixteen years ago I set
six pairs of bar posts all split out of the butt end of the same white
oak log. One pair I set butts down; another pair, one butt down, the
other top down; the others top down. Four years ago those set butt down
were all rotted off, and had to be replaced by new ones. This summer I
had occasion to reset those that were set top down: I found them all
sound enough to reset. My experiments have convinced me that the best
way is to set them tops down.” Other instances might be given in favour
of placing posts in an inverted position in the ground. Posts will
sometimes decay, for the following reason: The ends are often sawn off
with a coarse implement and left spongy, with the longitudinal fibres
shaken or broken a considerable way within the extremity of the wood. In
this state the ends of the posts must be apt to absorb from the ground
the moisture, which, being retained, and speedily pervading the whole
internal surface, _especially if painted_, appears to cause decay.
With respect to the preservation of wooden fences, Mr. Cruikshank, of
Marcassie, gives in detail various experiments from which it appears
that--1st. When larch or pine wood is to be exposed to the weather, or
to be put in the ground, no bark should be left on. 2nd. When posts are
to be put in the ground, no earth should be put round them, but stones.
3rd. When a wooden fence is to be put up, a No. 4 or No. 5 wire should be
stretched in place of, or alongside the upper rail.
Mr. G. S. Hartig, in the ‘Revue Horticole,’ gives the results of
experiments made with great care and patience, upon woods buried
in the earth. Pieces of wood of various kinds 3⅛th inches square,
were buried about one inch below the surface of the ground, and they
decayed in the following order: the lime, American birch, alder,
and the trembling-leaved poplar, in three years; the common willow,
horse-chestnut, and plane, in four years; the maple, red beech, and
common birch, in five years; the elm, ash, hornbeam, and Lombardy
poplar, in six years; the oak, Scotch fir, Weymouth pine, and silver
fir, were only decayed to the depth of half an inch in seven years;
the larch, common juniper, red cedar, and arbor vitæ, at the end of
the last-mentioned period remained uninjured. The duration of their
respective woods greatly depends on their age and quality; specimens from
young trees decaying much quicker than those from sound old trees; and,
when well seasoned, they, of course, last much longer than when buried in
an unseasoned state. In experiments with the woods cut into thin boards,
decay proceeded in the following order: the plane, horse-chestnut,
poplar, American birch, red beech, hornbeam, alder, ash, maple, silver
fir, Scotch fir, elm, Weymouth pine, larch, locust oak.
Before quitting the subject of decay of timber when buried in the earth,
it will not be out of place to allude to the decay of railway sleepers,
taking for example those in India: English and American sleepers will be
dealt with more in detail hereafter.
Dr. Cleghorn, Conservator of Forests, Madras Presidency, India, considers
the decay of sleepers to arise in a great measure from the inferior
description of wood used. Mr. Bryce McMaster, Resident Engineer,
Salem, considers that the native wood sleepers in India have hitherto
been found for the most part to fail on the Madras Railway, between
30 and 40 per cent. requiring to be renewed annually. Mr. McMaster
undertook an investigation with a view of ascertaining the causes of
this deterioration, and whether those causes could be overcome so as to
render available the vast resources of India. Thirteen hundred sleepers
of sixteen different woods were submitted to careful examination and
scrutiny twice at an interval of one year. The sleepers were variously
placed, both on embankments and in cuttings; in some cases they were
entirely covered with ballast to a depth of 4 inches; while in others
they were as much as possible uncovered, and completely so from the rails
to the ends--the ballast being only raised 2 inches in the middle of
the way, and sloped off so as to carry away the water under the rails.
From these observations it appeared that only five woods, Chella wungé,
Kara mardá, Palai, Karúvalem, and Ilupé, were sound at the end of two
years, the other eleven not lasting even that time. Also, that when the
sleepers were uncovered, decay was less rapid than when they were buried
in the ballast. The plan of leaving the sleepers partially uncovered had
many advantages; it effected a saving of the ballast, allowed the defects
to be more quickly detected, and kept the sleepers drier. It had been
urged that the heat of the sun would split the sleepers and cause the
keys and treenails to shrink; but from experience it was found that while
among the “uncovered” sleepers there was a large proportion “beginning
to split,” or “useless from being split,” there was on the other hand,
among the “covered” sleepers, a still larger proportion “beginning to
rot,” or “useless from being rotten.” It was also noticed that of the
sleepers “beginning to rot,” 19 per cent. had commenced under one or
both chairs. This was due to the retention of moisture under them, and
might be remedied by tarring the seats of the chairs. As regarded the
treenails where the sleepers were rotten, the treenails were invariably
found to be in the same state; while, when the heads were exposed to the
sun, they were not loosened by shrinking. Another objection was, that the
road would be more likely to buckle and twist, but this was not found in
practice to be the case. Treenails made in India cost 2_l._ 10_s._ to
4_l._ per 1000, and the woods generally used for the purpose are Vengé,
Kara mardá, Erul, Porasa, or satin wood, and Trincomalee. The three
woods first named are also extensively employed for keys, but teak keys
seem to be the best, and their cost does not exceed 6_l._ per 1000. From
the experience of the Indian engineers it appears that Teak, Saul, Sisso,
Pedowk, Kara mardá, Acha, Vengé, Chella wungé, Palai, Erul, Karúvalem,
will make very good sleepers to be used plain.
The sleepers which have failed on the Madras Railway might well be
divided into two classes,--those which were originally of perishable
woods, and were therefore unfit for the purpose; and those which although
of good wood had been cut from young trees, and not been allowed to
stand until old enough. The first arose from want of experience of the
nature of Indian woods: the second from the absence of a proper system of
working the jungles.
The wooden sleepers on the Indian railways should be tarred under the
seats of the chairs, be laid in dry ballast, and raised slightly in the
middle, and sloped off so as to throw the water under the rails. About
two-thirds of the Indian woods are practically useless owing to the want
of proper artificial means for preserving those of a perishable nature.
The subject of the decay of wood in India and tropical climates is too
extensive to be further considered here; but is of sufficient importance
to demand a volume to itself; the renewal of decayed wooden sleepers
to railways forming annually a most important item in foreign railway
budgets.
We have heard that some of our fortifications which have been erected
within the last few years to protect our English coast from invasion,
have already been invaded by dry rot. If this be true, some one well
acquainted with the subject should at once be appointed to find out the
cause, and recommend the remedy in each case.
Professional men, if they wish their works to “live for ever,” should
consider the after consequences of neglecting to provide against dry
rot. If the fungi could speak from under floors, ceiled-up roofs, behind
wainscots, girders, &c., we should often hear them exclaim, “A nice moist
piece of wood! Surely this belongs to us.” On the beams of a building at
Crawley, a carpenter many years ago cut a few words; they are full of
meaning in connection with our subject, and they run as follows:
“Man of weal, beware; beware before of what cometh behind.”