1911 Encyclopædia Britannica/Timber
TIMBER, the term given to wood cut and shaped for building purposes, or growing wood suitable for such purposes; in English law the tenant for life may not cut such trees (see Waste). The word appears in many forms in various Teutonic languages, meaning originally material to be used for building purposes; in the case of Ger. zimmer, and Du. timmer, both meaning “room,” the word has been transferred to the structures made of this material. The root is seen in Gr. δέμειν, to build, and Lat. domus, house.
The wood used in building is obtained from trees of the class known to botanists as exogens, or those trees which grow larger by the addition each year of a layer of new wood on their outer surface. A transverse section of a tree of this class shows it to consist of three distinct parts: the pith or medulla, the wood, made up of annual rings or layers, and the bark. The pith is in the centre of the tree and around it the wood is disposed in approximately concentric rings; that part near the pith is hard and close in grain, and from its position is termed heart-wood. The sap-wood is made up of the outer layers or rings, and these are softer than the heart and generally of more open grain. Each annual ring is made up of two parts—an inner soft portion light in colour, and a hard, dark-coloured outer portion. The inner portion is formed early in the season and is termed “spring wood,” the darker part being called “autumn wood.” The medullary rays extend radially from the centre of the tree to the bark at right angles to the grain of the wood, and serve during life to bind the whole together as well as to convey nourishment from one part of the tree to another.
The greatest care should be exercised in the selection of trees for felling. If the tree is too young the proportion of sap-wood is large, and the heart-wood is not so hard as that of a tree of mature age. The wood of an old tree, on the other hand, Felling Timber. has lost a great part of its toughness, and is of bad colour, brittle and often predisposed to decay. In trees that have arrived at a mature age the heart-wood is in its largest proportion and the sap-wood is firm and elastic; and the timber from such trees is of the strongest, toughest and most durable character. The age at which the northern pine and Norway fir arrive at maturity is between seventy and one hundred years. The larch, elm and ash should be felled when the trees are between the ages of fifty and one hundred years. The oak should be about one hundred years old when it is cut. The best time of the year for felling timber is in midsummer or midwinter, when the sap of the tree is at rest; it is not desirable to cut timber in the spring or autumn. By some authorities it is considered a good plan to remove the bark in the early spring and fell the tree in the ensuing winter.
Fig. 1.Fig. 2.
As soon as possible after felling, logs should be converted by sawing into scantling sizes, for if the log is left to dry or season, it is liable on shrinking to split. The usual method is to saw a log into planks or boards by cutting it into slices longitudinally as shown in Conversion of Timber. fig. 1; this is called bastard sawing, and is the most economical method, but, as will be seen in the diagram, the quality of the boards will vary very much, some consisting almost entirely of sap-wood cut at a tangent to the annular rings such as 𝑎, 𝑏, 𝑐, whilst the centre boards contain the heartwood cut in the best way at right angles across the annual rings as 𝑑, 𝑒, 𝑓. For oak and other hard woods another method of conversion is often adopted, called quarter sawing. The log is first cut into quarters and then sawn diagonally (fig. 2). In oak this develops the beautiful silver grain by cutting longitudinally through the medullary rays. Timber is now generally sawn into marketable sizes in the country of its growth, and shipped as scantling timber. Definitions and sizes are given below of the most usual forms of sawn timber:—
A log is the trunk of a tree with the bark removed and branches lopped.
A balk is a log hewn or sawn to a square section, and varying in size from 11 to 18 in. square.
Planks are parallel-sided pieces of timber from 2 to 6 in. thick, 11 or more ins. wide, and from 8 to 21 ft. long.
Deals are similar pieces 9 in. wide, and 2 to 4 in. thick.
Battens are similar to deals, but not more than 7 in. wide; Pieces of planks, deals and battens under 8 ft. long are called ends. Many of the soft woods, such as pine and fir, are sold by the standard. The standard of measurement most in use is the St Petersburg standard, which contains 165 cubic ft. or 720 lineal ft. of 11 in. by 3 in.
A load of sawn or hewn timber contains 50 cub. ft., and a load of unhewn timber 40 cubic ft.
A square is a superficial measurement, used chiefly for boarding, and contains 100 sq. ft.
letters painted on the ends. Swedish timber is stencilled with red letters or devices, the inferior qualities in blue. Prussian timber is scribed on the sides near the middle. By scribing is meant that the distinguishing letters are roughly cut in with a gouge. Russian timber is dry-stamped or hammer-branded on the ends. American (Canadian) timber is stencilled in black and white. United States timber is marked with red chalk on the sides.
To fit timber for use in building construction the superfluous sap and moisture contained in the green wood must be evaporated, either by natural or artificial means. During this process the wood shrinks considerably, and unless much care and attention are given to the drying wood it will warp and shake sufficiently to unfit it for practical uses. After the log is converted into scantlings, or “lumber,” as it is termed in America, it is stacked in the timber yard under covered sheds with open sides to enable it to “season.” The wood is carefully piled in tiers or courses, with strips Seasoning. of wood about an inch thick between each layer, so as to allow of the free circulation of air all round each piece. This is the natural and best method of seasoning, and timber treated in this way is more durable than that seasoned by artificial methods; the time taken, however, is much longer. For joiners' work the drying of the wood is often hastened by stacking the timber in well-ventilated rooms kept at a temperature of from 80° to 150° F. The time taken in seasoning wood by this desiccating process is not more -than one-tenth of that occupied in the natural or open-air method. Where it is convenient, timber is sometimes treated with a water seasoning process which enables it to be more easily dried. The wood is placed in a running stream and so tied or chained down as to be entirely submerged. The water enters the pores of the wood (which should be placed with the butt end pointing up stream) and dissolves and forces out the sap. After about two weeks in this position it is taken out and stacked in open sheds to be dried in the natural way, or treated by warm air in special chambers. Steaming and boiling are sometimes resorted to as artificial means of seasoning, but not to any great extent, as the timber deteriorates under such treatment, and the cost of the process is in many cases prohibitive. When wood is required to be bent, however, this is often the method that is adopted to soften the material, so as to allow it to be bent easily. The time allowed in the English government dockyards for the natural process of seasoning for hard woods such as oak is, for pieces 24 in. sq. and upwards, 26 months; from 16 in. to 20 in. sq., 18 months; from 8 in. to 12 in. sq., 10 months; from 4 in. to 8 in. sq., 6 months. Soft woods are allowed half these periods. When the wood is required in a “dry” state for joiners' work, twice the length of time is given. Planks are allowed from a half to two-thirds of the above time, according to their thickness.
Deals with coarse annual rings (i.e. coarse grain) should be rejected for good work, as also should those with waney or naturally bevelled edges. The wide annual rings show that the tree was grown too quickly, probably in marshy ground. Timber with waney edges has a large proportion of sap-wood, and is cut either from a small tree or from the outer portion Defects in Timber. of a large one, the waney edge being obviously due to irregularities in the surface of the tree. “Cup shake” is a natural splitting in the interior of the tree between two of the annular rings. It is supposed to be caused in severe weather by the freezing of the ascending sap. “Heart shake” is often found in old trees and extends from the pith or heart of the tree towards the circumference. When there are fissures radiating in several directions it is called “star shake.” “Upsets” are the result of some crushing force or violent shock to the balk or log. “Foxey” timber is tinged with dull red or yellow stains, indicating incipient decay. “Doatiness,” similarly, is a speckled or spotted stain denoting decay in certain varieties of timber, such as beech and some kinds of oak.
The primary causes of decay in timber are the presence, of sap, exposure to conditions alternately wet and dry, and want of efficient ventilation, especially if accompanied by a warm and moist atmosphere. Timber is most durable when it is kept quite dry and well ventilated, but some varieties last an indefinite period when kept continually under water. When, on the other hand, the wood becomes alternately wet and dry, “wet rot” results. The wood affected shrivels up and becomes reduced after a time to a fine brown powder. It is only by actual contact that wet rot affects the surrounding good wood, and if the decayed timber is cut out the remainder of the wood will be found to be unaffected.
“Dry rot,” which usually attacks the sap-wood, generally starts in a warm damp unventilated place, and is caused by the growth of fungi, some of which are visible to the naked eye, some microscopic. The spores from the fungi on the decayed wood float in the air and alight on any adjacent timber, infecting this also if the conditions be favourable. In this way the disease is spread rapidly, continually eating into the timber, which is first rendered brittle, and then reduced to powder. A strong growth of the fungus gives the appearance of mildew on the wood, and produces an unpleasant musty smell. The spores of the fungus will find a way through brickwork, concrete and similar material, in order to reach woodwork that may be on the other side. Dampness and a close atmosphere are essential to the growth of dry rot, and it is under these conditions that it spreads most quickly, the fungus soon dying when exposed to the fresh air.
There will be little danger of the decay of timber used in the construction of ordinary buildings if care has been taken, in the first place, to have it well seasoned, and, in the second, to ensure its being well ventilated when fixed in position. There are, however, several preservative processes to which timber may be subjected when it is to be fixed in positions which favour its decay (see also Dry Rot). In creosoting, which was invented by J. Bethell and patented by him in 1838, the timber is impregnated with oil of tar. This may be done by soaking the wood in the hot oil for several hours, but the better way is to place the seasoned timber in an iron chamber in which a partial vacuum is created by exhausting the air. The creosote is then forced in at a pressure of from 100 ℔ to 160 ℔ to the sq. in., according to -the size of the timber. In warm weather the pressure need not be so great as in winter. The whole process only occupies from two to three hours. Soft woods take up from 10 to 12 ℔ to the cub. ft.; hard woods are not usually treated by this process. Kyan’s process, patented in 1832, consists in impregnating the timber with corrosive sublimate which, acting on the albumen in the wood, converts it into an indecomposable substance. Boucherie, a Frenchman, originated a system in which the sap is expelled from the timber under pressure, and a strong solution of copper sulphate is then injected at the end of the wood. In Blythe’s process the timber is dried, and crude carbolic acid injected. In Burnett’s process a solution of zinc chloride is forced into the pores of the wood. A new process of preserving timber by means of steam heat has been tried and seems to be effectual. The wood is placed in closed chambers and steam admitted at high pressure (200 ℔ to the sq. in.). The heat and pressure together exert a chemical action upon the sap, which becomes insoluble and itself preserves the wood from decay.
Posts that are to be fixed in the ground should have their buried ends either charred or else well tarred. External woodwork may be protected by painting or oiling.
The timber used in building is obtained from trees which may be classed under two heads: (1) Coniferous or needle-leaved trees; (2) the non-coniferous or broad-leaved trees.
Coniferous Trees.—This class includes most of the soft woods which furnish timber for the framing and constructional portions of nearly all building work. They are also used for the finishing joinery of the ordinary class of building. The numerous varieties of pine which are used . more extensively than any other kind of wood are included in Varieties. this class.
The northern pine (Pinus sylvestris) has a number of other names and may be referred to under any of the following: Scotch fir, red deal, red fir, yellow deal, yellow fir, Baltic pine, Baltic fir. It grows in Sweden, Norway, Russia, Germany and Great Britain, and often gets a name from the port of shipment, such as Memel fir, Danzig fir, Riga fir, and so on. The colour of the wood of the different growths of northern pine varies considerably, the general characteristics being a light reddish yellow colour. The annual rings are well defined, each ring consisting of a hard and a soft portion, respectively dark and light in colour. No medullary rays are visible; the wood is straight in the grain, durable, strong and elastic, easy to work, and is used by the carpenter for internal and external constructional work, and by the joiner for his fittings. Tar, pitch and turpentine are obtained from the wood of this tree, which weighs from 30 to 38 ℔ per cub. ft.
The white fir, or Norway spruce (Abies excelsa), is exported from Russia, Sweden and Norway, where it grows in enormous quantity. It is the tallest and straightest of European firs, growing with a slender trunk to a height of from 80 to 100 ft. Like the northern pine, it is called by several names, such as “spruce,” “white deal,” “white wood,” “Norway fir.” The colour of the cut wood is a very light yellowish or brownish white, the hard parts of the annual rings being of a darker shade. A characteristic feature is the large number of very hard black knots which the wood contains. It is easy to work, but rather inferior in all respects to the northern pine. Its weight per cubic foot averages about 33 ℔.
The red pine (Pinus resinosa or P. rubra) is also known as “Canadian pine” and “American deal.” It grows in the northern parts of North America, where the tree attains a height of 60 or 70 ft. with a diameter of from 12 to 30 in. It weighs about 36 ℔ to the cubic foot. In Canada it is called “Norway pine” and “red pine” from the colour of the bark. The wood is white, tinged with yellow or red, of fine grain, and works to a smooth lustrous surface remarkably free from knots.
The white pine (Pinus strobus) is exported from the northern parts of the United States of America and from Canada. Other names for this timber are “yellow pine” and “Weymouth pine,” the last name originating in the fact that the earl of Weymouth first introduced it into England. The tree attains a height of from 150 to 200 ft. with a thickness of trunk at 5 ft. from the bottom of from 5 to 10 ft. The wood when cut is white or yellowish white, straight in grain and easily worked, but is not so tough, elastic or durable as the northern pine, and therefore is not so suitable for constructional work. For joiners' work, however, it is well adapted, and glue adheres strongly to it, though nails do not hold well. It weighs about 30 ft per cub. ft.
The Kauri pine (Dammara australis) is a native of New Zealand. It grows to a height of from 80 to 140 ft., with a straight stem 4 to 8 ft. in diameter. The wood is a light yellowish brown in colour, fine in grain and of even texture, the annular rings being marked by a darker line. It is strong, elastic and resinous. A cubic foot weighs about 35 to 40 ℔.
The pitch pine (Pinus rigida) is a native of Canada and is common throughout the United States of America. It is remarkable for the large quantity of resin it contains, the weight of the wood, which is about 48 ℔ per cub. ft., and the strong red markings of the grain, usually straight but sometimes exhibiting a beautiful figure. Its weight and strength, and the large size of the balks, make it very valuable for heavy constructional works and piling, and its fine figure makes it equally valuable for joinery.
Of the larch the best known variety is the European larch (Larix europaea), which grows in Switzerland, Italy, Russia and Germany. The larch frequently attains a height of 100 ft. but the average height is about 50 ft. and diameter 3 ft. The wood is extremely durable and lasts well where exposed alternately to wet and dry ; indeed, the larch is useful for every purpose of building, internal and external. It is the hardest and toughest of the cone-bearing trees and weighs 30 to 40 ℔ per cub. ft. ; it has a straight grain free from many knots; in colour it is of a rather deep yellow or brownish tint, with the hard portions of the annular rings marked in a darker red. The American black larch (Larix pendula) and the American red larch (Larix microcarpa) are native to North America. The latter tree is of comparatively little service. The black larch yields timber of good quality, nearly equal to that of the European tree.
The cedar used in building work is really a species of juniper. The Virginian red cedar (Juniperus virginiana) grows in the United States, Canada and the West Indies. The tree produces excellent timber, and is much used for furniture, its strong acrid taste driving away insects. It weighs about 40 ℔ per cub. ft. The Bermuda cedar (Juniperus bermudiana) is used for internal joinery and is extremely durable.
Hard Woods.—The timbers in the second class are obtained from non-coniferous trees, containing no turpentine or resin, and are given the general name of hard woods. Their initial expense and the high cost of working preclude their general use, and they are consequently reserved to a great extent for specially heavy constructional work and ornamental finishing joinery.
The oak (Quercus), of which some sixty distinct species are known, grows freely in Europe and America. Several kinds yield valuable timber: in England the two best-known varieties are-Quercus pedunculata and Quercus sessiliflora. There is little difference between the quality of the two woods, the variation being in the foliage and fruit. The wood is very hard, tough, with fine regular grain and close texture, the annular rings being distinct and the medullary rays well marked. When it is cut along these rays beautiful markings are revealed, called silver grain. The colour is a light brown, and its weight is about 50 to 56 ℔ per cub. ft. Oak is very durable either in a dry or a wet situation, or in a position where it will be alternately dry and wet. It is very suitable for constructional and engineering works, and it supplies one of the finest woods for ornamental joinery work. The Durmast oak grows in France and the south of England ; it is not so strong or durable as the English oak. Baltic oak is grown in Norway, Russia and Germany, and is exported .from the Baltic ports. Though inferior to the English oak, it is very straight in the grain and free from knots. Austrian oak is light in colour, and is much used for joinery work. White oak comes principally from Canada, under the name of American oak. It is straight in grain but subject to warping, and is not so durable as British oak.
The common walnut (Juglans regia) grows in Great Britain. On account of its scarcity it is little used for building purposes, except for ornamental joinery, being_ more used by the cabinet and furniture maker. A cubic foot weighs about 45 ℔. The white walnut (Juglans alba) or hickory is common in North America, and is very tough, hard and elastic. The black walnut (Juglans nigra) is also native to America. It has a fine grain with beautiful figure, and takes a fine polish. It weighs 56 ℔ per cub. ft.
Of the elm (Ulmus) there are five common varieties, the two most cultivated being the rough-leaved elm (Ulmus campestris), which is grown in large quantities in England and North America, and the smooth-leaved wych elm (Ulmus glabra). The colour of the wood is brown; it is hard, heavy, strong and very tough, and when kept either always wet or always dry is durable. Elm is very liable to warp and shake, is porous and usually cross-grained. The piles of old London Bridge were of elm, and after six centuries of immersion were but little decayed. The wood is not much used in building operations. It weighs about 40 ℔ per cub. ft.
The common ash (Fraxinus excelsior) is a native of Europe and Northern Asia, and is grown extensively in Great Britain. Its colour is light brown, sometimes with a greenish tint, with the annular rings of darker colour. The wood is very tough and strong, and superior to most wood in elasticity; and it weighs 40 to 55 ℔ per cub. ft.
Beech (Fagus sylvatica) grows in the temperate districts of Europe. The wood is heavy, strong and hard; white to light reddish-brown in colour; and durable if kept either dry or wet; is porous and works easily; it weighs about 40 to 48 ℔ per cub. ft. The red beech (Fagus ferrugina) is common in North America.
Sycamore (Acer pseudo-platanus), sometimes mistakenly called the plane tree, is common in Germany and Britain and in the eastern states of North America. It is a large tree of rapid growth. The wood is light brown or yellowish white, with annular rings not very distinct, often cross-grained and of uniformly coarse texture. It warps and cracks rather badly, and weighs from 35 to 42 ℔ per cub. ft.
Teak (Tectona grandis) is a native of southern India and Burma. It grows rapidly to a great height, often exceeding 150 ft., with a straight trunk and spreading branches. Teak wood is straight in the grain and exceptionally strong and durable, its oily nature enabling it to resist the attacks of insects and to preserve iron nails and fastenings. It weighs from 45 to 56 ℔ per cub. ft.
Mahogany (Swietenia mahogani) is a native of the West Indies and Central America, the best-known varieties being Cuban or Spanish and Honduras. The Spanish wood has a darker colour and richer figure than the Honduras, and is therefore preferred for ornamental joinery work. The colour of mahogany is reddish brown, and in the Cuban wood the pores are often filled with a white chalky substance which is usually absent in the Honduras variety; the latter, however, may be obtained in larger sizes, and is straighter in the grain and easier to work. Spanish mahogany weighs about 56 ℔ to the cubic ft., and the Honduras variety about 36 ℔.
Greenheart (Nectandra rodiaei) is a very heavy, hard and durable wood from the East Indies. It ranges in colour from pale yellow to a deep brown, and the grain is very compact and of close texture. The wood contains an oil which enables it to resist the attack of sea worms, and this quality makes it suitable for use in marine construction. The average weight of a cubic foot is about 61 ℔.
Basswood (Tilia americana) is common in Canada and in the northern United States. It is soft and easy to work, and of even texture and straight grain. It may be obtained in wide boards, and thus is fitted for use in large panels. It weighs about 30 ℔ per cub. ft.
There are several varieties of maple growing in Canada and the United States, but the one in most common use is the sugar maple, also called rock maple, which grows freely in the districts around the Great Lakes. The wood is fine-grained, frequently with a beautiful wavy figure, yellowish white to light brown in colour; it is very hard, tough and durable. Birds’-eye maple has a peculiar curly grain, and is much in request for ornamental joinery.
The numerous tests of the strength of timber which have been made by various authorities from time to time vary so much, both as regards the conditions under which they were carried out and the results obtained, that Strength of Timber. great discretion is required in using them for any practical purpose. An important series of tests was made in 1883 and 1887 at Munich by Professor Johann Bauschinger. He reduced all the specimens submitted for test to a standard of moisture, the percentage selected being 15%. This was necessary on account of the great difference in strength found to exist between specimens cut from the same piece of timber but differing in the amount of moisture they contained. In America, Professor J. B. Johnson made a large number of tests for the Forest Department of the Board of Agriculture of the United States between 1891 and 1895. More than 300 trees were cut down and experimented with, the species under test embracing ten different kinds of pine and five different varieties of hard-wood trees. Records were made as to the nature of the soil and climate where the trees were grown; their conditions of growth, their age and size, and the season of felling. As in the tests made by Bauschinger, the percentage of moisture contained in the wood was very carefully observed, and it was found that this amount of moisture has a very great influence upon the resisting power of the wood, the strength increasing with the dryness of the material up to 3 or 4% of moisture, at which point the greatest strength of the wood is reached. Wood in such a dry condition, however, is never found in actual practice, timber in an ordinary well-warmed and well-ventilated situation probably containing at least 10%.
One general conclusion arrived at both by Bauschinger and Johnson was that the strength is much affected by the specific gravity of the timber. In all cases the strength increases proportionately with the density of the wood. A most complete series of tests upon the physical characteristics of the hard woods of Western Australia was completed for the government of Western Australia by G. A. Julius in 1907. This work was carried out in a most thorough manner, and as many as 16,000 tests were made, the conditions of test being based upon those laid down by Johnson. The results serve to show the great value of Australian timbers, and the comparisons made with the typical timbers of many other countries emphasize the fact that the Australian woods are equal to any in the world for hardness, strength and durability.
For use under special conditions a wood suited to the particular requirements must be selected. The following is a list of the best timbers for different situations: for general construction, spruce and pine of the different varieties; for heavy constructions, pitch pine, oak (preferably of English growth), teak, jarrah; for constructions immersed in water, Baltic pine, elm, oak, teak, jarrah; for very dry situations, spruce, pines, mahogany, teak, birch, sycamore.
There are no regulations in England limiting the working stresses that may safely be placed upon timber, although in some districts the least sizes that may be used for timbers in roofs and floors are specified. In some European and other countries. however, the safe working stresses of timber used for constructional purposes are defined. The building by-laws of the municipality of Johannesburg, in South Africa, contain the following table:—
| Material. | Tensional. | Compressive. | Bending. Extreme Fibre Stress. |
| Timber | |||
| Fir and Pine | 12 | 12 | 12 |
| Hardwood | 12 | 13 | 12 |
Note.—The compression stresses are for short struts and columns where the length does not exceed for timber 15 times the least transverse dimension, and where the ends are fixed. Where the ratio of the length to the least transverse dimension is higher, the load per square inch shall be proportionately reduced. No post of timber shall exceed in length 30 times its least transverse dimension.
References.—T. Tredgold, Principles of Carpentry, § xii.; R. E. Grandy, Timber Importer's Guide; G. A. Julius, Report of a Series of Tests upon the Physical Characteristics of the Hardwoods of Western Australia (1906–1907); J. B. Johnson, Report of Tests upon Timber made for the Forest Department of the Board of Agriculture of the United States (1891–1895); J. Bauschinger, “Report of Tests made upon Timber at Munich,” Mittheilungen aus dem Mechanisch-Technischen Laboratorium der K. Technischen Hochschule in München; F. E. Kidder, Building Construction and Superintendence, vol. ii.; Rivington, Notes on Building Construction, vol. iii.; T. Laslett, Timber and Timber Trees; H. Stone, The Timbers of Commerce and their Identification; H. M. Ward, Timber and some of its Diseases; R. Hartig, Timbers and How to know them; J. Brown, The Forester; G. S. Boulger, Wood. (J. Bt.)