This article will introduce one of the most important resources used in construction - wood. Wood is the inner part of a tree, located under the bark. Wood is widely used in industry and everyday life. Its high hardness, density and strength are key factors. But in the selection of high-quality material there are a number of shortcomings, which implies wood defects.
Let's focus on the main ones:
Wood defects shortcomings, features and defects of wood, both the entire trunk and its individual sections, which are various deviations from the norm, are named. Existing deviations reduce the quality and value of wood and limit its practical use.
Typically, defects are formed when a tree grows in unfavorable conditions, when the trunk is damaged by pests (wood grinders, bark beetles, etc.) or fungi, or when the fibers are rotting (see figure). These are primary wood defects that occur during the overall growth process of the tree.
Mechanical defects of wood. Processing defects
Deviations from the ideal structure occur during logging, for example, poor-quality felling and an incorrectly chosen direction of tree fall, causing the butt to split. During the processing process, mechanical defects in wood are revealed - these are processing defects. They are distinguished in the following types: wane, risks, and damage of a local nature, for example with a saw, is called a cut, waviness, fluffiness, mossiness, scuffing, gouges. A torn end is characterized by the presence of small indentations, tufts or small particles of wood, or burrs on the end of the part. Mechanical defects also include: flake, chip, dent, grinding, occurs fringe continuous and intermittent - ribbons of bundles of fibers or wood that have not completely separated on the edges of the parts, burns.
Lumber products change shape when stored, dried, moistened or sawed. These changes are classified as warping and have different degrees (see figure).
Lumber is also subject to defects - rot, cracks, wormholes, which are secondary defects that arise during storage and use of wood.
Features and defects of wood are divided into 9 groups of defects. The main ones:
Bitches- This is the first of the groups that bears the main variety-forming defect, combining two types: knots and eyes. The woody content of the knots has a finer structure of the annual layers and a dark color; they are the base of the branches, which are enclosed in the wood of the trunk itself. Happens as a species open knot, so overgrown knot.
Overgrown knots They have no varieties and are found exclusively in round materials.
Trunk shape defects growing trees are distinguished in the following types:
Curvature(see figure) is a versatile or unilateral curvature of the trunk along its entire length. There are simple and complex (several bends in different directions) types of curvature, which make sawing difficult and produce a lot of waste.
Zakomelistost(see fig.) when sawing, produces low-quality material, the appearance big amount cut fibers. This is a thickening of the butt of the trunk in relation to the entire trunk.
Royki– this is a ribbed butt, when cut transversely at the end of the trunk it looks like a star-lobed arrangement of annual fibers. This material is highly warped and has reduced strength.
Growths on the trunk are accompanied by curling of the wood, which is more common in deciduous trees - this is a local sharp thickening of the trunk.
Surges most often found on the butt part of the trunk. Accompanied by smooth growths on the surface. Mouth guards expressed in a more prominent form, arising in places of dormant buds, look in the form of drops.
Defects in the structure of wood (see figure) are divided into the following types: roll; fiber inclination; traction wood; curl; curliness; pockets; eyes; core, double and mixed core; germination; stepson; cancer; dry side; tarred; false nucleus; internal sapwood; spotting and cross-layering. Let's look at the main types.
Cross-layer characterizes the different direction of deviation of the fibers from the axis of the tree. The lateral load of such wood is poorly perceived. Curlyness refers to a type of fiber inclination - a wavy arrangement of fibers. Curl– this is the curvature of the local character of the annual layers.
Kren found more often in wood coniferous species, changes in structure occur in compressed areas of the trunk and branches. These are arched areas that form in curved trunks or obliquely growing trees. There is a displacement of the core during cross cutting. This defect contributes to the warping of boards and beams, reducing the strength and uniformity of the material structure.
Double core clearly expressed when cross-cutting a log. The tree trunk in this place most often has an oval shape. Between the cores it is usually observed germination in the form of overgrown bark. This deficiency leads to cracking, processing difficulties and increased wood waste.
Internal sapwood expressed at the end of the trunk in the form of several or one ring-layers of different widths, having a lighter color than the core of the wood. This group of annual layers in the core of wood has the properties, structure and color of sapwood. This defect is characteristic of deciduous trees, often found in ash and oak.
False core is the inner part of the trunk with a dark color in different shades. Shapes include round, lobed, star-shaped and eccentric. The darker color of the false heartwood differs from the sapwood.
Pocket is a cavity filled with gums or resins located inside the annual layers. Such resin pockets reduce the strength of the wood, spoil the surface and cannot be glued and finished.
At curliness wood fibers are placed wavy, especially at the butt of the tree. This material is highly valued when molding sliced veneer, but the processing process itself is difficult to handle. This defect is characterized by the formation of growths and swellings at the root part of the trunk.
Sprouting called a defect in a separate area that appears as a result of mechanical damage (tarring, mushroom spots). In this case, not only the appearance deteriorates, but finishing becomes more difficult.
Curl– this is the curvature of the annual layers due to the influence of trunk knots or shoots. They can be one-way or end-to-end. This defect reduces strength, so it is not used in the manufacture of parts that carry additional load. Defects such as resin pockets, tar and heel are characteristic of the group of coniferous species.
spotting- these are strips colored differently than the entire body of the trunk, which do not affect the hardness of the wood. Spotting appears during tree growth.
Grinding This is a section of softwood material that is heavily impregnated with resin. Places are darker in color. Resin has no effect on strength and is less susceptible to rotting, but makes it difficult general finishing material and painting.
Chemical wood stains- these are unnaturally uniformly colored areas in wood that arose as a result of the development of biochemical and chemical processes, in most cases this is associated with the process of oxidation of tanning components. usually found in the upper layers of wood. When the material dries, they most often fade.
Fungal lesions- this is a group of defects that occurs with the participation of fungi, which can either cause the destruction of wood or not at all affect its strength, but have the property of changing color.
There are only 6 types of such fungal infections: mold, mushroom sound spots, sapwood mushroom stains(color spots – dark and light, deep, superficial and sublayer), browning(lateral and end), rot And hollow.
Mold has the appearance of a continuous coating or stain on areas of the wood surface. It appears during damp storage of timber and colors the surface of the wood pink, black and other colors, which depend on the color of the mycelium and spores.
Fungal sound spots do not reduce the strength of wood, they arise in the core of the tree under the influence of wood-destroying and wood-staining fungi. They are recognized in various forms - rings, holes, a continuous affected area in the center of the trunk, often extending to the periphery.
Sapwood mushroom stains– these are areas of colored sapwood affected by a wood-staining fungus that does not cause rot in felled wood. It is noted in the form of stripes, elongated spots or entire surface lesions. These colors are characteristic of coniferous species. Fungi cause blue, greenish or gray coloration. Light colors do not mask the wood texture, dark colors of sapwood paint it in dark tones and mask the texture. Deep sapwood colors penetrate into the texture to a depth of more than 2 mm, and sublayer colors are located at some distance from the general surface.
Browning affects deciduous trees with a brown color. In felled wood, biochemical processes occur that reduce the hardness of the wood. The brown color during end browning originates from the end and goes along all the fibers. Lateral browning begins from the side surface and spreads towards the center of the timber.
Rot- these are areas of wood that are abnormal in overall color, which may or may not reduce the hardness of the material, arising from the influence of wood-decaying fungi. The first stages of fungal infection do not change the quality and value of the wood, but only change the color of some areas.
It has several varieties, distinguishable by color and structure: variegated sieve, brown fissured, white fibrous.
The types are distinguishable in the following types: sapwood (soft and hard), external rotten and sound.
Variegated sieve rot is characterized by reduced hardness and variegated color. Such wood retains its integrity for a long time, later it becomes soft and splits. Brown cracked rot causes cracking of the material along and across the fibers. White fiber rot attacks lignin and cellulose and discolors the wood in a marbled pattern. When severely damaged, it easily splits and crumbles.
The type of sapwood rot has pinkish-brown or yellowish-brown hues in softwoods, and a marble-like pattern in hardwoods. The hard type of this rot is close to the same hardness as the surrounding wood. Soft sapwood rot has reduced hardness.
External rotten rot occurs both in the sapwood part of the timber and in the core. This brown, cracked rot occurs when improper and long-term storage under constant strong influence of wood-decaying fungi.
Core rot occurs in the core of a tree during growth and is characterized by reduced hardness. The first stages of such rot do not affect mechanical performance. Appears in the form of elongated spots or stripes.
Foreign inclusions imply the presence of a foreign body in materials that is not of wood origin (nail, stone, wire, metal fragment). Externally, this presence can be determined by the following signs: folds or swellings of the bark, dents, holes, changes in the color of the surrounding wood. Such defects require additional processing of the timber.
There are two large groups of tree species: coniferous and deciduous. Conifers belong toPine - one of the most common and accessible types of wood in Russia. The more common species is Scots pine. Pine has a straight trunk, and therefore is a convenient material for construction. Pine, growing in northern forests, is characterized by the greatest straightness of the trunk. Its high abrasiveness also favors the use of pine in construction. Among its other properties, one can note dense and durable wood, a core heavily impregnated with resin, due to which pine wood is less susceptible to rotting. Pine wood is light, which combined with strength makes it a very good quality. Early pine wood is yellowish-white (width from 20 to 80 annual layers), sharply different from the reddish-brown core wood. Pine is widely used in the manufacture of various crafts. Pine has properties that should be paid attention to by those who are going to work with it, and especially by those who are going to engage in wood carving. Pine wood is very scratchy and, in addition, has a fairly pronounced striped texture. These two properties of pine significantly limit its use in carved crafts: it is best used when making large elements. As a rule, pine cuts and saws well, especially if the pine has little resin. However, you need to remember that as it dries, its causticity increases and it becomes more difficult to cut. Since pine wood is heterogeneous (pine tree rings are separated from each other by wood with resin ducts), it is poorly suited for making small items and crafts. It is better to use pine in large carvings with large patterns, for example, in house carvings.
Spruce - for the most part its characteristics resemble pine. It is also one of the most common and accessible breeds. However, spruce wood is lighter and has more knots. The knots are located at right angles, and therefore have round shape. Knots are sometimes so hard that you can break a tool on them. It contains less resin, as a result of which the spruce rots faster. Due to its knotty nature, spruce wood is much more difficult to process. In addition, the following can be noted distinctive features spruce wood: compared to pine, spruce darkens more slowly, although its final tone does not differ from that of pine. Freshly planed spruce wood is slightly lighter than pine wood. Unlike pine wood, late wood of spruce has the appearance of a light brown stripe, which gradually turns into yellowish early wood. Spruce growing in the north is better in quality than spruce growing in the south. The same can be said about pine. The growths on spruce trees are very beautiful, but they are very rare.
In our forests you can find two species cedar: Siberian cedar and Korean cedar. In terms of its characteristics, cedar is somewhat inferior to pine. However, from the point of view of resistance, against rotting and cracking, cedar turns out to be a more advantageous species. Cedar lends itself well to processing. Cedar wood has a pinkish tint. Late wood is yellowish-pink in color, transitions into early wood gradually, without a sharp contrast. Tree rings vary across all sections. Cedar has a very beautiful texture. It is used in carved sculpture and in the manufacture of other carved and turned products.
Wood larches 
has high physical mechanical properties. Its strength is about a third greater than that of pine. Because of this, it is an indispensable material in construction. Larch floors can last for many years, and it is difficult to find wood that is superior to larch. In addition, larch is little susceptible to rotting. Larch is also used in furniture production because it has a fairly beautiful texture. Larch wood has a brownish tint. The sapwood is narrow, approximately 15-20 annual layers wide. The kernel is more different dark color; the transition to sapwood is abrupt. The larch texture looks good after varnishing. Veneer is often made from it for finishing furniture. Larch wood is processed very well and is ideally suited for the manufacture of long products.
WOOD DEFECTS
Wood defects are those damages that entail changes in its appearance, tissue integrity, correctness of its structure and, as a consequence, deterioration in its quality and reduction in the possibilities of its use. Mechanical damage to wood is called defects.However, a lot depends on the intentions of the person working with the tree. If we're talking about not about carpentry work oh, and, for example, about carving, you need to remember that a defect in wood can turn into an advantageous property that a carver who approaches his work creatively can take advantage of.
Bitches are the most common wood defect. The disadvantages of knotty wood are the following: the appearance deteriorates, mechanical processing becomes difficult, and strength decreases (when stretched along the fibers and bending). The degree of knotiness of wood must be taken into account when performing joinery and carpentry work. In addition to healthy knots, there may also be rotten knots on the wood. Depending on the degree of decay, such knots are divided into rotten (rot has affected less than 1/3 of the knot), rotten (rot has affected at least 1/3 of the knot) and tobacco (rotten wood has been partially or completely replaced by a loose brown or whitish mass). It must be taken into account that rotten knots not only reduce the strength of the wood, but can also cause gradual rotting of the entire wooden piece.
Depending on the shape, quantity, size and causes of occurrence, several types are distinguished cracks Methic is internal longitudinal cracks extending from the core. Such cracks appear in the tree when it has not yet been cut down, and after cutting, as it dries, they increase in size. 
Cracks:
Frost cracks (frost cracks) also appear in a growing tree, as can be judged by the specific growths of wood and bark. Such cracks can run through the entire assortment. This must be taken into account, since the ends of the crack can be located in different planes, and therefore the crack itself can be curved, “not flat”.
Crack cracks are called cracks that form between the annual layers. These cracks also occur in the growing tree and increase during the drying process.
Shrinkage cracks are cracks that appear in an already cut tree as it dries out. Their appearance is caused by stresses inside the wood. Shrinkage cracks are somewhat smaller in size than the cracks listed above, however, they can reach a length of one meter.
Among trunk shape defects It should be noted the convexity, growths and curvature.
Taperedness is a decrease in the diameter of the trunk towards its top or upper cut, exceeding 1 cm per 1 running line. m. Curing increases the amount of waste when processing lumber and reduces their strength. The latter occurs because when sawing materials along the fibers, the integrity of a significant part of them is violated.
A growth is a thickening of the trunk with twisted wood. Build-up occurs on all types of wood, but is most common on hardwood. Wood processing becomes more complicated due to growths. However, the growths have a very beautiful texture, and therefore can be used in furniture finishing and artistic products, primarily as facing veneer. The growths of elm, walnut and elm are of the greatest value.
Curvature is the curvature of the tree along its axis. The curvature of round timber increases the amount of waste during processing, and also leads to the appearance of radial inclination of the fibers in lumber and veneer.
Wood structural defects, as a rule, also complicate processing and make the wood practically unsuitable for carpentry. At the same time, structural defects in wood have a certain decorative value. In other words, we are again faced with the same situation: a disadvantage, depending on the type of work and its goals, can often turn into a positive quality. This should never be forgotten, especially for those who want to become an all-rounder.
We will focus on such defects as curling, bending of fibers, curl, resin pocket. There are other vices; We refer those who want to learn more about them to specialized literature, especially since they are of purely special interest, and knowledge about them can hardly be useful to a carpenter or woodcarver.
Defects in the structure of the trunk:
Curling is a tortuous or random arrangement of wood fibers, which reduces the strength of wood during bending, compression and tension. " " -
The inclination of the fibers is a non-parallel arrangement of wood fibers relative to its axis. With the so-called tangential inclination of the fibers, the resin ducts, core rays, as well as cracks in the wood appear to be twisted and do not run strictly along the log. The tangential inclination of the fibers causes increased shrinkage and warping of wood.
A curl is a local curvature of the annual layers, usually caused by the presence of knots.
The resin pocket is a resin-filled cavity inside the annual layer. This wood defect is found in coniferous species, most often in spruce. It negatively affects the appearance of wood, its strength, gluing ability, and also interferes with its facial finishing.
At fungal infection of wood it begins to rot or changes color. It should be noted that not all fungal infections are very dangerous for wood. Thus, there are fungal infections that only change the color of the wood; they do not affect the mechanical properties of wood, but spoil its appearance and increase water permeability, and can also destroy adhesives and varnishes. Consequently, a number of fungal infections pose a danger primarily to the appearance of wood and products made from it. However, in a significant number of cases, a change in color indicates the beginning of decay. Wood affected by rot is not suitable for use.
The fungus can affect both a growing tree and felled wood.
It must be remembered that wood affected by fungus is dangerous source infection. Therefore, it is recommended to carefully inspect the wood before storing it.
Danger insect damage to wood It mainly threatens freshly cut wood. However, insects can also damage dry wood in products.
Wood defects and processing defects
Processing defects
Wood defects of mechanical origin that arose in it during the process of harvesting, transportation, mechanical processing and sorting are called defects .
TO processing defects relate foreign inclusions , processing defects and warping of wood.
Foreign inclusions.
Foreign bodies of non-wood origin (stones, sand, wire, nails and metal fragments) present in wood make wood processing difficult and often cause accidents.
Processing defects.
They appear on wood as a result of the action on it cutting tools. These include wane, risks, waviness, fluffiness, mossiness, scuffing, gouges, torn end, burr, gash, nick, flake, chip, dent, sanding, fringe and burn.
Obzol (picture on the right, a, b ) - part of the side surface of a log preserved on edged lumber or parts. There are blunt wane, which occupies part of the width of the edge, and sharp wane, which occupies the entire width of the edge. Wane makes it difficult to use lumber for its intended purpose and increases the amount of waste when sawing.
Risks - these are periodically repeating deep marks left on the surface by the cutting parts of tools (saw teeth, knives, etc.).
Waviness - not a flat cut. The presence of individual fibers on the surface that give the wood roughness is called hairiness.
Mossiness - these are whole bundles of fibers and small particles of wood on the surface of the part.
Badasses - partially separated and raised above the surface of the material sections of wood with clawed edges.
Gouges - These are small depressions often located on the surface of the part, formed as a result of the separation of bundles of fibers or wood particles.
Torn end characterized by the presence on the surface of the end of the part of frequently located small depressions and bundles of incompletely separated fibers and small particles of wood.
Burr - a visor with a sharp, pinched shape adjacent to the longitudinal edge of the part.
Local damage to the surface of wood by tools, such as a saw, is called washed down .
flake - a through side crack extending from the end.
Skol - this is an area with split wood in the end zone.
Dent characterized by a depression on the surface of the lumber, formed as a result of local compression of the wood.
Sanding - removal during grinding of part of the part below the surface being processed.
Fringe - a continuous or intermittent strip of tufts, incompletely separated fibers and wood particles on the edges of lumber.
Darkening and partial charring of the surface of parts under the influence of high temperatures, arising from increased friction of cutting tools on wood, is called burn .
Warped . This change in the shape of lumber occurs during sawing, drying or storage (Fig. on the left). It makes it difficult to use lumber and blanks for their intended purpose. Drying and moistening the wood leads to a change in the degree of warping.
Warped Yes:
a - simple longitudinal along the surface; b - complex; c - longitudinal along the edge; g - transverse; d - wingedness; n - deflection.
Wood defects
The disadvantages of wood are some of its defects. All of them limit the use of wood in industrial production, but can be valuable in the manufacture of decorative products.
Here are the main vices:
Bitches.
Cracks.
Defects in the shape of the trunk.
Defects in the structure of wood.
Chemical stains.
Fungal infections.
Biological damage.
Foreign inclusions, mechanical damage and processing defects.
Warped.
Bitches.
There are two types of knots - open knot and overgrown knot.
Open knot has several varieties:
according to the shape of the cut on the surface of the assortment (round, oval, oblong);
by position in the assortment (layer, edge, edge, end, stitched);
by relative location (scattered, grouped, branched);
according to the degree of fusion (fused, partially fused, unfused, prolapsed);
according to the condition of the wood (healthy, healthy light, healthy dark, healthy with cracks, rotten, rotten, tobacco);
at the exit to the surface (one-sided, through).
Overgrown knot It is detected only in round timber and has no varieties.
Bitches - the main variety-forming defect, since they have a negative effect when using wood. They disrupt the homogeneity of the structure and cause curvature of fibers and annual layers, which reduces the mechanical properties of wood. The wood of healthy knots has increased hardness compared to the hardness of the surrounding wood, so the knots make it difficult to process with cutting tools. Tobacco knots in round assortments are accompanied by internal rot.
| Light healthy | Dark healthy | Rotten | Ramified |
| Rib | Stitched | Group | Tobacco |
Cracks.
Cracks are divided into types:
By type:
metic (simple and complex);
spanking;
frosty;
crack shrinkage.
By position in the assortment
:
lateral;
reservoir;
edge;
end
By depth:
not through (shallow and deep);
end-to-end
Width:
closed;
dispersed.
| Plastevye | Edge | Face | |
 |
 |
 |
Methic cracks |
 |
 |
 |
Frosty cracks |
 |
 |
 |
Peeling cracks |
Cracks appear in wood as it grows. Their formation is influenced by natural factors and internal stresses that arise in the trunk. There are frost, peel and metic cracks.
Frosty cracks appear as a result of the expansion of internal moisture during severe frosts. As a result, through cracks appear, directed radially. Internal stresses arising in the trunk lead to the appearance of peeling (separation of annual layers from each other) and metic (running along the trunk from the butt to the top) cracks. In addition, when drying wood, cracks may appear as a result of drying. .
Defects in the shape of the trunk.
The following types are distinguished:
conciseness;
backbone (rounded and ribbed);
ovality;
growth;
curvature (simple and complex).
Curvature- this is the curvature of the longitudinal axis of the trunk. It can be simple or complex (the trunk has several bends in different directions). The curvature in round timber makes it difficult to use and increases the amount of waste in the woodworking industry.
Zakomelistost- this is a thickening or increase in the diameter of the butt in relation to the tree trunk. When making boards from this part of the trunk, large waste is inevitable; the resulting material when sawing is of low quality, as it appears a large number of cut fibers.
Royki- longitudinal depressions in the butt part of the trunk. The cross cut of the end of the log looks star-shaped with a wavy arrangement of growth rings. When cutting into boards, most of the trunk is discarded as waste, since such boards warp greatly and have reduced strength.
Growths- sharp local thickening of the trunk, have twisted wood. In most cases, they are found on deciduous trees: birch, maple, alder, oak and some others, and sometimes on conifers. There are two types of growths - nodules and burls.
Surges- an internal disease of the tree, accompanied by growths with a smooth surface, most often found on the butt part of the tree.
Mouth guards- expressed by a more relief surface; when cleared of bark, the relief appears in the form of drops. They appear in place of dormant buds that intensively appear on the tree.
Defects in the structure of wood.
The following types are distinguished here:
fiber inclination;
roll;
traction wood;
curliness;
curl;
eyes;
pocket;
core;
double core;
mixed core;
stepson;
dry side;
germination;
cancer;
tarred;
false nucleus;
spotting;
internal sapwood;
cross-layered.
Cross-layer (inclination of fibers) represents various deviations of the direction of the fibers from the longitudinal axis of the tree. Wood with such a defect does not tolerate lateral loads well. Varieties of cross-layer include curl (wavy arrangement of fibers) and curl (local curvature of the annual layers).
Kren- change in the structure of coniferous wood in the compressed zone of the trunk and branches. It is observed in the form of arcuate areas. It often forms in the wood of twisted and inclined trunks. In a cross section, especially in conifers, the displacement of the core to one side is clearly visible. The heel disrupts the homogeneity of the wood structure, reduces strength, and contributes to strong longitudinal warping of boards and beams.
Double core. It is clearly expressed when the trunk is cut transversely at the bifurcation site. The end of the tree in this place usually has an oval shape. Often there is a closed growth (overgrown bark) between two cores. It makes processing difficult, increases waste, and promotes cracking.
Internal sapwood- a group of annual rings-layers located in the heartwood, having the color, properties and structure of sapwood. At the end of the trunk it is clearly expressed in the form of one or several rings of different widths, lighter than the core of the wood. This defect is observed in the trunks of deciduous trees, especially oak and ash. Its sections are located in the heartwood and have the color of sapwood. Continuous or discontinuous rings of double sapwood consist of soft wood, which subsequently contributes to cracking of the sawn material. Double sapwood is found in oak, ash and some other hardwoods. This defect is very valuable for mosaic work. In deciduous and coniferous trees there are sometimes areas where natural conditions the wood takes on a different color. The color tones of such areas are darker and lighter than the main color tone of the wood layers. In deciduous species the color is brownish-red, in coniferous species it is light yellow.
False core- the inside of the trunk is dark colored in various shades. The shape of the false nucleus can be: round, eccentric, star-shaped, lobed. False heartwood differs from sapwood in that it is darker in color. 
a - tangential inclination of the fibers;
c - curliness;
g - curl;
d - eyes;
e - false nucleus.
Pocket- a cavity inside the annual layers filled with resin or gums. A resin pocket spoils the surface of products, is difficult to finish and glue, stains tools, and reduces the strength of wood.
Curlyness- This is a wavy arrangement of fibers, especially in the root part of the tree. Most often, curling is observed in maple, oak, Karelian birch, walnut, etc. Wood with this defect is difficult to process, but in the manufacture of sliced veneer it is highly valued, especially in walnut and maple. In this regard, swellings are also characteristic - growths on the root part of the trunk
Sprouting- a defect in a section of wood resulting from mechanical damage to the fiber. Such a section of wood spoils the appearance and makes finishing difficult. Mushroom spots and tar marks are often found in this area.
Curl characterized by local curvature of the annual layers due to the influence of sprouts or trunk knots. Curls can be end-to-end or one-sided. Parts that must bear a significant load are made of wood without curls that reduce its strength. Resin pockets, heels and tars are characteristic of conifers, especially spruce.
spotting expressed in the color of the sapwood in the form of oblong veins. In color they resemble the heartwood of wood. This defect is a consequence of fungal infections of the fiber. It is located mainly on the boundary layer of the core and sapwood.
Grinding- This is a section of wood heavily impregnated with resin. Occurs at the site of injury to the trunk of coniferous trees. Resined areas are distinguished by a darker color. The wood at the point of defect is heavier than the main one. Resin reduces impact strength, reduces the water permeability of wood, and makes gluing and finishing difficult.
| Mushroom sound spots and stripes |
Brown cracked rot |
Sineva | Pied Sieve rot |
| White fibrous rot |
Browning | Soft sapwood rot |
Outdoor rotten rot |
Wood, like any natural material, imperfect. In addition to the fact that it rots and burns, it also has quite a lot of defects, due to which most of the outwardly beautiful logs and boards are rejected and used for the production of glued materials, plywood and particle boards. What wood defects exist? There are several groups of wood defects:
Naturally, all these defects apply not only to round timber, but also to beams, carriages, boards, all kinds of blanks and veneer. But some defects are characteristic only of round lumber, others - for beams and blanks, and others - only for veneer. There are also defects that are inherent in all three types of lumber.
Knots are the most common wood defect. Depending on the type of lumber, knots can be classified by structure, location, degree of fusion, cut shape, etc. This defect is typical for all types of lumber, but has a greater impact on the rejection of boards and veneer, especially if the wood species is valuable. Cracks are also quite common, and they can also be confidently called a defect in any timber. Defects in the shape of the trunk increase the rejection rate not only of those logs that will be used for construction, but also those intended for peeling. Defects in the structure of wood for round material and beams are practically invisible, unless there is a growth or burl on the tree. Such defects are rejected in boards, blanks and veneer, although often it is the curls or curls that give a wood product an extraordinary charm. Chemical stains are the enemy of veneer and all kinds of furniture blanks, but other lumber is not rejected for this defect. But fungal infections are a defect for absolutely all materials, especially if they are wood-destroying fungi. As for biological damage, such as wormholes or areas pecked out by birds, depending on the extent of the damage, this defect can also apply to any timber.
Let's take a closer look at each of the wood defects:
The first wood defect is knots
Due to the fact that wood is a living material, knots in it are simply inevitable. They are the base or even an ingrown part of the branches, and, being in the wood, the knots disrupt its uniformity, causing curvature of the annual layers and fibers. This defect also leads to a reduction in the working cross-section of the tree, can greatly complicate its mechanical processing, and almost always worsens the appearance of the final products and workpieces. The strength of wood due to the presence of knots is reduced, sometimes by 30-40%, and in thin pieces this percentage can be even higher.
Knots are divided into varieties according to several parameters:
Based on the degree of knot overgrowth in round lumber, there are two types: open and closed. Open ones are those that go to the surface of the log. Overgrown knots are called closed; they can be detected only by local swellings and curvatures of the fiber directions. The shape of the cut of knots in lumber and veneer can be round, oval or oblong; it is determined by the angle of cutting the wood and the ratio of the larger to the smaller diameter of the knot.
The position of the knot in sawn wood can be different:
If the knot extends onto the narrow side of the workpiece, then it is called an edge knot, and if it extends onto the wide side, it is called a face knot. Accordingly, edge knots come out on the edges, and end knots - on the ends. In the case where a knot extends onto two edges and the face or edge between them, it is called stitched. There are also two more types of knots: one-sided and through. A one-sided knot extends only onto one side or edge, while a through knot “pierces” the workpiece through and through, exiting on opposite sides of the lumber.
Based on the relative position of knots in lumber, three types of knots are distinguished: group, scattered and branched. Group knots are those located on a segment of length less than or equal to the width of the workpiece. If the knots are located at a distance from each other greater than the size of the board or timber, then they are called scattered. The whorled arrangement of branches, characteristic of larch and pine, leads to the formation of branched (fingered) knots quite often.
The degree of fusion of a knot with the surrounding wood largely determines the effect of this defect on the strength and appearance of the lumber. According to the degree of fusion, knots can be: fused, partially fused, or unfused. If the annual rings of a knot have not grown together with the wood for less than 0.25% of the perimeter of the knot's cut, then such a knot is called fused. If there is no fusion within 0.25-0.75%, then the knot is partially fused. Knots that are not fused over more than 0.75% of their own cut perimeter are called unfused. Unfused knots can be held in the wood by pressure and adhesion, or they can fall out.
The condition of the wood around the knot is also important for all types of timber. According to this parameter, all knots are divided into:
If the wood of a knot has absolutely no signs of rot, then such a knot is called healthy. For veneer and lumber, all healthy knots are divided into colored (light, slightly dark and dark) and cracked. Rotten and decayed are called knots that have a rotten zone of more or less than 1/3 of the cut area of the knot, respectively. If the rot has turned into dust, a mass of rusty-brown or whitish hue, which is easily ground into dust, then the knot is called tobacco.
The characteristics of lumber in terms of knotiness are compiled according to the types, sizes and number of knots. The most difficult material for identifying the types of knots is a log, since even by the condition of the wood it can be difficult, for example, to distinguish rotting knots from tobacco ones. To do this, probes are used to measure the depth of spread of rot and the affected area. If round timber is used for veneer, then the depth of the closed knots is important, but if it is used for construction, then this characteristic is not important. In veneer and lumber, all types of knots are determined visually and according to basic relationships. Knot sizes are measured in any of two ways: by the smallest diameter or by the distance between a pair of tangents drawn parallel to the longitudinal axis of the workpiece.
The degree of influence of a knot on the physical and mechanical properties of lumber depends on the characteristics of the knot itself and the condition of the workpiece, i.e. internal stress and expected load. And the least influence is exerted by healthy, round knots that are well fused with the surrounding wood.
Natural and acquired cracks
One of the main defects of wood is cracks. Violating the integrity of the timber, they significantly reduce product yield premium, lead to a decrease in strength building materials, and also contribute to the penetration of fungal spores and moisture into logs, beams or boards. What are cracks and what types do they come in?
Cracks are breaks in wood along the grain. They appear both in growing trees and in cut ones. There are several types of cracks:
Methic cracks are located radially in the trunk and can extend along the trunk for 10 meters or more, sometimes reaching from the butt to the crown. They appear in a growing tree, and when the wood dries, they expand. Notice metic cracks in round material it is possible only at the ends, since they never reach the side surface. There are simple and complex metic cracks in lumber. Simple ones are located in the same plane and can be found on the ends or side surfaces. Complex ones are located in different planes. Frost cracks are longitudinal external breaks that extend radially into the trunk. Such cracks form from a sharp decrease in temperature in winter time. They are located mainly in the butt part of the trunk, often coming out with wood ridges and bark along the edges. Frost cracks are clearly visible in round material on the ends and side surfaces, and in lumber they are found as long radial tears with local widening of growth rings around.
Spalling cracks are called separations along the growth rings inside the core or in the mature wood of growing trees. They are found in round material only at the ends, and they have the appearance of arcuate or annular cracks. In lumber, delaminations can be crater cracks (at the ends) and longitudinal cracks (on the side surfaces). Peeling cracks do not appear yet established reasons, it is likely that the peeling is due to internal rot or watershed.
All these three types of cracks are natural, i.e. they appear as the tree grows. Shrinkage cracks are an acquired wood defect that arises from strong internal stresses during drying. Shrinkage cracks spread deep into the trunk from the side surface in radial directions and are characterized by a short length (standard up to 1 meter) and small depth. They can occur due to uneven drying along the length of round lumber, and with large cross-sections of hardwood, internal cracks, so-called fistulas, often appear. The latter can only be detected when cutting the material.
Tree trunk shape defects
Non-standard trunk shapes for the most part lead to an increase in the amount of waste during peeling and sawing round timber. In addition, a defect in the shape of the trunk is the main reason for the radial inclination of wood fibers in veneer and lumber. Defects in the shape of the trunk are natural; they are all divided into several varieties:
The difference in trunk diameters at the root and the top is not a defect, but a natural pattern, if its indicator remains within normal limits. Any trunk gradually decreases in diameter from the butt to the top, and if for every meter of trunk length the diameter narrows by 1 cm or more, then this trunk is said to have a taper.
Backwardness is a type of runawayness when it occurs sharp increase diameter of the butt part of the trunk. Those. The diameter of round timber at the butt end is 20% greater than the diameter of the log at a distance of 1 meter from this end. If the cross-section of the butt part is almost round, then the butt part is called rounded. There is also ribbed burrowing, when there are longitudinal depressions on the side of round timber.
Ovality is a defect when the end of round timber is not round, but ellipsoidal. Wherein largest diameter exceeds the smaller one by at least 1.5 times. Ovality is almost always accompanied by structural defects in the wood. Growths on trees are quite common and are the result of exposure to bacteria, viruses, fungi, radiation, and mechanical damage to the tree during any period of growth. The shape of the growths can be very different, from small smooth protrusions to huge burls and bulges. On a longitudinal section of the burl, the structure of the wood is twisted, and in suvel the growth rings are curved along the outer contours of the growth. All growths make woodworking difficult, but burls are highly valued as a material for veneering sliced veneer and making decorative items.
Often tree trunks have varying degrees of curvature. This may occur due to the loss of a top shoot and its replacement by a lateral one; the tree may also have a tilt towards more light. On mountain slopes and cliffs, trees may become crooked due to constant wind. The curvature can be simple or complex, i.e. with one bend or several.
Wood structural defects
Structural defects of wood are deviations from the standard structure. The following types of defects are distinguished:
Grain slope, also called cross-grain, is determined differently for roundwood or sawn products. On logs, the cross-layer is detected in the direction of the bark grooves on the side surface, as well as along screw cracks. In lumber and veneer, a distinction is made between tangential and radial inclination of the fibers. Tangential inclination can be associated with the spiral structure of the fibers, and it also occurs when sawing straight-grained material when the cut is directed at an angle to the longitudinal axis of the log or board. The radial inclination of the fibers appears when radial sawing, which is why it is also called artificial cross-layer.
The stronger the slope of the fibers, the lower the strength of the wood, this is especially noticeable during static bending and stretching along the growth of the fibers. In addition, the slope of the fibers significantly increases the percentage of shrinkage and is often the cause of helical warping (winging). Mechanical restoration also becomes difficult if there is an inclination of the fibers.
Curling is a disordered and tortuous arrangement of fibers. It is more common in deciduous trees. The curl may be wavy or tangled. Wavy curling has a more or less ordered arrangement of wavy-curved fibers and a streaky structure. A similar arrangement of fibers can be observed mainly in the butt part of the log, where the trunk passes into the beginning of the root system. Confused curling differs from wavy curling in the random arrangement of fibers; it can be seen in the wood of burls and other growths.
Curling is mostly a local defect in the structure of the wood, but it also occurs throughout almost the entire trunk, as in Karelian birch. Curling reduces the tensile strength of wood and makes machining difficult. But along with this, the grain gives a very beautiful structure to the wood. Wood with a tangled twist is especially highly valued, and this defect is often called conditional.
A curl is a local curvature of annual layers near knots and sprouts. The curl can be one-sided or end-to-end. For large lumber, curls are almost not considered a defect if they are one-sided. But for small workpieces, both types of curls are quite dangerous.
Reactive wood is formed in curved or inclined trunks under the influence of gravity, wind load, osmotic pressure or growth stresses; it tends to return to the original position of the trunk, and therefore is called reactive. There are two types of reactive wood:
Leaning is a structural defect in wood, which is expressed in the apparent broadening of the later part of the annual layers. But lurch wood only resembles late wood in color. The heel is formed mostly in the compressible part of inclined and curved trunks. A distinction is made between continuous and local heeling. The first can be found at the ends of the trunks in the form of dark oval-shaped areas of wood. The annual layers in such wood are much wider, and the transition from the light zone of the layer to the dark zone is less clearly expressed. A continuous roll is characteristic of the butt part of an inclined trunk, the stretch zone of a curved trunk and the compressed part of the branches. Local heel appears during short-term bends. It can be seen at the end of the trunk in the form of arched sections that cover one or more annual layers. Continuous and local heel is found on the side surfaces of lumber in the form of dull dark stripes of varying widths.
Heel leads to an increase in density, end hardness and compressive strength along the grain of wood, but at the same time heel reduces the tensile strength along the grain and impact strength. The presence of heel in wood leads to a decrease in cellulose and an increase in the cost of bleaching it. The most dangerous thing about lurch wood is that shrinkage along the grain is very strong, and transverse shrinkage is half that of ordinary wood. This leads to the lumber warping and cracking.
Traction wood is formed in the stretched zone of twisted and inclined trunks. This defect manifests itself in a sharp widening of the annual layers. At the ends of the timber, traction wood is noticeable in the form of arched areas with a fleecy surface and a different color. On the veneer or radial surface of the workpiece, traction wood is observed in the form of strands - narrow strips.
Traction wood has a higher density, increased longitudinal shrinkage, but rather low transverse shrinkage. In terms of cellulose content, traction wood is superior to ordinary wood. Mechanical processing of traction wood is quite difficult, since the fleecy surface has excessive viscosity.
Chemical coloring of wood
The color of wood is given by tannins, dyes and resins found in the cavities of the cells. With age, wood can change color, generally darkening. But not only the age of the tree affects the color; there are several types of chemical coloring of wood, which are often defects if the lumber is harvested for subsequent peeling or sawing into finishing materials. In general, the term “chemical coloring” refers to a uniform or uneven color that appears in growing or harvested wood as a result of a chemical reaction.
Types of chemical stains:
Water stains form on the surface of the material in the form of stripes or spots due to the contact of wood with water. Wood yellowing is the light yellow color of the sapwood of driftwood, which appears during intensive drying. Brown coloring is characteristic only of poplar; it appears in growing trees on smooth areas of the bark in the form of black-brown spots. Such marks are almost not etched and remain on the lumber.
The red core is often called a false core, since this red color is observed in the central part of the end of the log, and it passes through almost the entire trunk. The boundaries of the false nucleus often do not coincide with the growth rings. The red core may be round, lobed or star-shaped. There are several reasons for the appearance of a false nucleus: exposure to fungi, exposure to frost, wound reaction or age-related tissue differentiation.
Produbina - surface color (red-brown or bluish-brown), having a depth of no more than 5 mm. A hole appears as a result of the oxidation of tannins in those tree species whose bark is rich in these tannins.
Chemical coloring of wood does not affect the physical and mechanical properties of the material, and as a result of drying it fades to a greater extent, so it is a defect only when the wood is used for decorative items, and colored spots or streaks do not disappear after treatment.
Fungal infections of wood
Fungal infections of wood are caused by simple organisms - fungi that develop from spores. These spores are carried by wind, water, insects, animals, etc. Based on their effect on wood, there are two main types of fungi: wood-staining and wood-destroying.
Wood-staining fungi are quite harmless, since they have almost no effect on the physical and mechanical properties of the material. These fungi infect growing forests and lumber until the wood has lost all its juices. Wood-staining fungal infections include sapwood and heartwood stains different colors, mold, browning. More dangerous are wood-decaying fungi, which change the color and structure of wood, forming rot. Rot can be sapwood (formed in the sapwood), heart rot (in the core) and external rot.
Sapwood rot is characteristic of dead wood and felled forests and can develop if the humidity is quite high. At an early stage, heart rot appears only as small spots of various colors, and it is difficult to distinguish it from damage caused by wood-staining fungi. There are several types of heart rot:
In cut lumber, variegated sieve rot stops developing, unlike the other two types of rot, especially if the wood is not dried.
External rotten rot appears both in the sapwood and in the core of the tree if the lumber is stored incorrectly for a long time, i.e. at high humidity and a temperature suitable for the development of fungi. This rot can occur already in finished products from wood when conditions are also unfavorable. There are even special names for fungi that destroy any wood in a few months - real house mushroom, filmy house mushroom, white house mushroom.
It is difficult to distinguish wood-staining fungi from destructive rot, and therefore, when fungal infections are detected, the wood is treated with special antiseptic solutions, eliminating the fungi. If fungal infections or rot cannot be eliminated in a wood workpiece, then the workpiece is considered unsuitable for subsequent processing.
Biological damage to wood
A wormhole is the destruction of wood by beetles and larvae. Larvae leave internal passages different sizes and forms that can be seen by removing the bark from the trunk. There are several types of wormholes: superficial, shallow, deep and through.
The lightest damage, a superficial wormhole, penetrates to a depth of no more than 3 mm, i.e. Only the bark and bast layer are damaged. This wormhole can not be considered a vice, since it does not affect negative influence on the mechanical properties of the material.
A shallow wormhole penetrates to a depth of up to 5 mm in lumber and up to 15 mm in round wood. A deep wormhole is called a wormhole in which the depth of penetration of passages in lumber is more than 5 mm, and in round timber - more than 15 mm. A through wormhole is an extreme case of a deep one, when the passages of the larvae pierce the material right through. These types of wormholes reduce the mechanical properties of wood and disrupt its integrity, and in addition, fungi can penetrate into the tree along with the larvae. This means that wormwood can rot or crumble into dust in a matter of months. It is not recommended to use such wood for the construction of load-bearing structures, for finishing premises, making furniture, etc. This material is only suitable for crafts.
Dead trees and those that were cut down relatively recently are more susceptible to wormholes. On an industrial scale, wood is checked for the presence of wormholes in a standard way - the bark is removed and the cleanliness of the trunk is examined. The depth of the wormhole is measured with a probe.
False wood core.
This is the name given to the dark inner zone that does not coincide with the growth rings. This happens due to bacteria, fungi, severe frosts, and mechanical damage. False heartwood has low flexibility, but is superior to sapwood in strength.
Heartwood
Core. The central part of the trunk, which has loose wood, is called the pith. Logs with a core are not considered defective, but for lumber such a defect is unacceptable due to susceptibility to cracking and rot.
Wood knots
Bitches are traces from the bases of branches. They can have a round, oval, oblong shape. Knots affect the quality of wood in different ways. The most dangerous are considered to be knots with wood that is easily ground into powder (tobacco), and rotten ones.
Stepson of wood
Stepson called the stunted second tip of the trunk, which penetrates the tree trunk at a slight angle to the axis. As a rule, the stepsons stretch almost along the entire log, violating the integrity, uniformity, and strength of the timber.
Resin wood pocket
Resin pockets in wood they represent the space between the annual rings, filled with gums and resins. Their size varies from 1 mm to 15 cm. They are formed due to mechanical damage, exposure to insects, or heating by the sun in frosty weather.
Aquifer of wood
Water layer. In the core area there may be areas with high humidity. Because of this, during drying such wood cracks and deforms. When viewed longitudinally, the water layer looks like stripes stretching from the butt to the top; when viewed from the end, it looks like dark areas in the center.
Wood resin
Wood tarring. This is the name given to areas of coniferous wood impregnated with resin in the area of mechanical damage. Tarred wood is difficult to glue and process, but is very dense and resistant to rotting.
Of course, this is not a complete classification of natural defects and defects in wood. More details on this issue can be found in GOST 2140-81
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