TIMBER AS A BUILDING MATERIAL

Before we understand what timber is, it is essential to talk about wood. ‘Wood’ in simple
words can be stated as a hard, fibrous structural tissue found in the stems and roots of trees
and other woody plants. Wood has been used for thousands of years by we humans.

Early humans used wood for various purposes, but primarily it was used as a fuel and even
as a construction material. For Example, they used to make huts out of wood; they also used
it for cooking purpose. Apart from this, wood had a wider range of use even then. This was
because it was readily available, and no elaborate or sophisticated tools were required to
work with it.

Wood comes from trees. The wood is fine, uniform structural tissue of a tree, and is fa vored
because of its exceptional cutting qualities, durability, rich color, and aroma. It is moderate
in hardness yet it is highly workable. The wood obtained from each tree has its potential,
specific quality and peculiarity but at the same time, it can be associated with a few flaws as
well. This is something crucial which one must take into consideration while understanding
the nature of wood.

Wood has been used as a building material for thousands of years, being second only to
stone in terms of its rich and storied history in the world of construction. It has evolved in
over the ages from natural material to a modern industrial and engineering material. Wood
has a unique ability to contribute for well-being of human being both as a material for use
and as a key element in the natural world of the forests.

Timber – Lumber:

The word ‘Timber’ is used to describe structural products of wood, while in North America;
the word ‘Lumber’ is used. ‘Wood’ is often used to describe the furniture and other non -
structural items.

Definition of Wood:

Different experts have defined wood in their own way. According to ‘Christopher Gorse’,
‘David Johnston’ and ‘Martin Pritchard’ (Author of Oxford Dictionary of Construction,
Surveying & Civil Engineering), Wood is a naturally occurring material obtained from trees.
According to ‘Catherine Soanes’, ‘Sara Hawker’ and ‘Julia Elliott’ (Author of Pocket
Oxford English Dictionary), Wood is a hard and fibrous substance which forms a significant
part of the trunk and branches of a tree.

Wood is a natural material that has been used for the construction of buildings, bridges and
various other structures since many centuries. Wood can be fabricated into all kinds of
shapes and sizes to fit practically any construction need.

Wood is further processed and transformed into timber, lumber etc. These days, with the
advances in science and technology, it is rapidly replaced by composite wood materials in
which natural wood is just an essential ingredient of a matrix or a laminate.

The latter is found to be more useful and adaptable as woods may be treated chemically,
thermally or otherwise as per requirements. Some examples are plywood, fiberboards,
chipboards, compressed wood, impregnated wood etc.
Timber is a remarkably a versatile material. Timber is used as a construction material
because of its fire resistance, good structural characteristics, insulating properties and
moreover, it is economically feasible. Naturally forming long slender elements ideal for
framing, it represents one of our oldest building materials. Relatively recent developments
in processing and technologies have provided products of timber for a wide range of
application. As wooden technologies overcome constraints, timber begins to compete with
steel and concrete.

Definition of Timber

According to ‘David Blockley’ (Author of New Dictionary of Civil Engineering), Timber is

a wood, which is prepared for building and carpentry use.
 Tree Classification Based on Mode of Growth
Timber is obtained from two broad categories of trees:

• Conifers Trees

• Deciduous Trees

These trees are further classified as softwood and hardwood. The terms ‘softwood’ and
‘hardwood’ do not exactly indicate softness or hardness of particular timbers. In fact, some
hardwoods are found to be softer and lighter than softwoods. The main differences between
hardwoods and softwoods are botanical, and relate to the way the tree grows.

01. Softwood

• Softwoods are obtained from Conifers or evergreen trees.

• Examples of softwood trees are Chir, Deodar, Fir, Kali, Pine, Spruce etc.

• Softwood has a relatively simple structure with long slender cells with flatted or tapered,
closed ends arranged in radial files.

• Softwoods are generally faster-growing and cheaper than hardwoods.

• They are considered less decorative and are typically less prone to moisture movement.

• According to ‘Madan Mehta’, ‘Walter Scarborough’ and ‘Diane Armpriest’ (Authors of

Building Construction), Softwood trees mature for harvesting two or three times faster
than hardwood trees.

• Approximately 75% of North American forests contain softwoods. Because of their faster
growth and relative abundance, softwoods are commonly used for structural framing of
the wood building in North America. Hence, in most of the buildings, floor joists, rafters,
ceiling joists, studs, sheathing are of softwood lumber.

02. Hardwood

• Hardwood is a dense wood obtained from a broad-leaved tree or Deciduous Trees.

• Examples of hardwoods are Mahogany, Oak, Sal, Teak, Greenheart, ash, beech etc.
 • The anatomy of hardwood is more varied and complicated than softwood with thicker
cell walls making primary tissue for strength.

• Generally, Hardwoods are used for flooring, finishing, where their higher densities
(which give excellent abrasion resistance) are useful.

• Hardwoods are also used for wall panelling, trims, cabinets, furniture because they have a
more interesting and varied grain structure.

Processing of Timber
Mentioned below are the four stages involved in timber processing,

01. Felling of Trees

• To get Timber, the trees are cut down or they naturally fall on the ground. This is known
as the felling of trees.

• The essential facts to be remembered in connection with felling of trees are age of trees
for felling, Method of felling and season for felling.
02. Seasoning of Timber

• When a tree is newly felled, it contains about 50 per cent or more of its dry weight as
water.

• Therefore, it is necessary to remove the water before the timber can be used for any
engineering purpose. So, timber seasoning is the process in which timber is dried.

03. Conversion of Timber

The process of cutting and sawing timber into suitable sections is known as the conversion
of timber. This process is carried out in timber yard with appropriate machinery at different
stages.
04. Preservation of Timber

Preservation of timber means protecting from fungi and insects attack so that the life of
timber is increased. The longevity of timber can be considerably increased by treating it
with certain chemicals grouped together as preservatives before use. The preservatives may
be water solvable salts or oil solvable salts or volatile base salts. The main objective of such
treatment is to ensure a longer, trouble-free life of timber. The objectives of preservation of
timber are:

• To increase the life of timber structure.

• To make the durable timber structures.

• To protect from the attack of destroying agencies such as fungi, insects etc.

The quality of timber depends on the environmental conditions of the locality, maturity of
the tree, methods of seasoning, process of preservation and time of felling. There are so
many characteristics that timber contains and make it suitable for various applications.

Timber

Properties of goodTimber

• It has uniform colour. Its light colour usually indicates timber with low strength.

• It is durable.

• It is hard.
 • It is capable of retaining its shape during conversion or seasoning.

• It provides good insulation from the cold.

• It is capable of taking loads slowly or suddenly.

• A good timber is free from serious defects like knots, shakes, flaws and cracks.

There are many structural and nonstructural applications of timber in building construction.
It is essential to clarify the terminology for its various uses.

Uses of Timber as a Building Material

Timber from well-managed forests is one of the sustainable resources. Timber is categorized
amongst the world’s most eco-friendly building solution. It ages naturally and is not
degraded into toxic product that damages the environment. In addition, timber is renewable
as it continually grown in plantations and forests. The various uses of timber are,

• It has good strength and hence used for making load-bearing members like beams,
columns, trusses and piles.

• It is naturally available, ready to use and economically feasible. The rough timber is used
for temporary works like scaffolding, centering of an arch etc.

• It can be easily cut and converted to any size and shape. Hence it is used for frame and
shutters of doors and windows, roofing materials, furniture etc.
Uses of Timber

• It has a very high strength to weight ratio, the capability of transferring both tension and
compression forces and is naturally suitable as a flexural member.

• It is also used for temporary bridges and boat construction.

• Timber also benefits from its natural growth characteristics. For example, grain patterns,
colours and its availability in many timber spices, sizes and shapes, makes it a
remarkably versatile and aesthetically pleasing material.

• Timber can be used for so many purposes, but has some advantages and
disadvantages.

Advantages of Timber
 • Timber can be easily shaped and modified. Remaining waste can be recycled. Timber
generates very few pollutants compared to other building products.

• Timber can be easily connected using nails, screws, dowels, bolts and connectors. Also,
under controlled conditions of temperature and humidity, adhesives may be used to
connect the timber element.

• Timber is light in weight and easy to handle in manufacture, transport and construction.

Disadvantages of Timber

• It is likely to crack, wrap, bend and decay, if not properly seasoned and not treated with
the preservatives.

• There are many applications for which timber is unsuitable due to durability issues.

• It requires careful regular maintenance.

• It is subjected to risk of fire. Timber can burn making it a less than ideal material to use
in applications where fire safety is a concern.

• If not readily available, it proves to be costly.

• It is also susceptible to termite attack if not maintained properly.

Though at least, Timber is also believed to be a ‘future material’. There are few building
materials which inherently possess the environmental benefits of wood. Timber is most
widely used building material because it has a range of varied characteristics that makes it
suitable for a wide range of application.

Timber is a natural and extensively utilized construction material extracted from trees.
Wood has been used for centuries, and it is still a relevant construction material today,
because of its versatile properties, its diversity and aesthetic qualities.

There are several inherent characteristics that make timber an ideal construction material.
These include its high strength to width ratio, its durability, performance and good
insulating properties against heat and sound. Timber is also a renewable resource and can
make an essential contribution to the achievement of sustainable building. Timber excels
where strength (or stiffness) to weight is more important than absolute strength (or stiffness)
 QUALITIES OF GOOD TIMBER
Good timber should have the following qualities

1. HARDNESS

A good quality timber should be hard enough to resist deterioration.

2. STRENGTH

It should have sufficient strength to resist heavy structural loads.

3. TOUGHNESS

It should have enough toughness to resist shocks due to vibrations. It should not break in bending
and should resist splitting. Timbers having narrow annual rings, are generally the strongest.

4. ELASTICITY

It should have the property of elasticity so as to regain its original shape after removal of loads.
This is a very important property to be considered if the timber is used in making sport goods.

5. DURABILITY

It should be able to resist attacks of fungi and worms and also atmospheric effects for a longer
period of time.

6. DEFECTS

Timber should be prepared from the heart of a sound tree and be free from sap, dead knots,
shakes and other similar defects.

7. FIBRES AND STRUCTURE

It should have straight and closed fibres and compact medullary rays. It should give a clear
ringing sound when struck. Dull heavy sound is an indication of internal decay. Its annual rings
should be uniform in shape and colour.
 Fig 1 - structure of a timber

8. APPEARANCE AND COLOUR

Freshly cut surface should give sweet smell and present shining surface. It should have dark
colour, as light colored timbers are generally weak in strength.

9. SHAPE AND WEIGHT

It should retain its shape during the process of seasoning. Heavy timbers are always stronger than
light weight timbers.

10. WORKABILITY

It should be well seasoned and easily workable. Teeth of saw should not get clogged during the
process of sawing. It should provide smoothened surface easily.
 Mechanical properties of wood
Mechanical properties of wood play an important role when used for different design
applications. Wood is widely used for structural purposes. This fact sheet summarizes some of
the basic concepts related to mechanical characteristics of wood, including viscoelasticity,
compression, shear, bending strength properties and how such characteristics should be taken
into consideration for an efficient practical design.

1. Viscoelasticity

In contrast to metals and plastics, wood is an orthotropic material, meaning its properties will be
independent in three directions – longitudinal, tangential and radial, as illustrated in Figure 1.
Another unique property of wood is its viscoelasticity, which can be described as having both
plastic and elastic characteristics when exposed to a certain deformation.

Figure 1. Orthotropic structure of wood.

Elastic materials easily stretch under an applied load. However, they return to their original
conditions once the load is released. In contrast, plastic materials stay at the stretched condition
even if the load is released after a long period time. The behavior of wood products is between
the above two types of conditions.

Example: A bookshelf example can be used to illustrate the viscoelasticity of wood: A number of
books are put on a shelf and, in time, it will have a limited amount of sagging deformation.
When all books are removed from the shelf, it will never return to its original flat condition.
Thus, there will be a residual deformation left because of its viscoelasticity. Figure 2 illustrates
the viscoelastic behavior of wood, as in the bookshelf example.

Figure 2. Viscoelastic behavior of wood.

2. Compression

Compression of wood and wood-based materials plays an important role in almost any
construction projects. If the compression strength or bending strength of a 2-inch by 4-inch beam
is not known, deflection due to bearing a load may cause significant deformation, which could
even lead to its failure during service life. Therefore, most softwood construction lumber is
graded based on allowable load resistance, which can be determined from a stress test. However,
strength properties of hardwood lumber are not that critical because a majority of it is used for
furniture manufacturing and is not exposed to substantial loads.
Compression or shear strength of a wood beam or truss used extensively for construction can be
calculated based on the following equation:

Sigma (σ) = P/A, where σ is stress, P is load and A is surface area.

In general, stress is the load per unit area and is expressed in pound per square inch (psi),
kilogram per square centimeter (kg/cm2) or any other units. Figures 3 and 4 show compression
and shear stress developed by a perpendicularly applied load on small wood blocks.

Figure 3. Compression parallel to grain.

 Figure 4. Sheer stress of a sample.

3. MOE and MOR

In the case of bending a beam, we are dealing with modulus of elasticity (MOE) and modulus of
rupture (MOR) to evaluate its load resistance. While MOE is a measure of the stiffness of a
body, MOR is related to maximum strength that can be resisted by a member. Both are expressed
as stress similar to most of the other mechanical properties of wood. The following two
equations are used to calculate MOE and MOR of wood with a rectangular cross section:

MOE = (P L3) / (48 I D)

MOR = (Pmax L) / (b d2)

I = (bd3) / 12

Where:
P = load below proportional limit (lb.)

Pmax = failure load (lb.)

L = test span (in.)

b = width of the sample (in.)

d = thickness of the sample (in.)

D = center deflection (in.)

I = moment of inertia, which is the inertia of a rigid body with respect to its rotation and, in the
case of a rectangular cross section, is expressed as in4.

In general, depending on the species, wood has MOE and MOR values of 800,000–2,500,000
psi and 5,000–15,000 psi, respectively. If a Red Oak with an approximate MOE value of
2,000,000 psi is used to make the bookshelf mentioned above, its deflection deformation will be
less than that of Aspen, which has a lower MOE.

Both MOE and MOR values of different species can be obtained from various references for a
particular design. Table 1 displays some of the mechanical properties, including MOE and MOR,
of several species. Figure 5 also illustrates a typical beam bending with deflection as a result of a
central load.
Table 1. Some of the mechanical properties of various species at 12 percent moisture content.
(From Wood Handbook, 1999)

Compression // Shear // to the grain

Douglas Fir MOE (psi) MOR (psi) Specific gravity
to the grain (psi) (psi)

Douglas Fir 1,950,000 12,400 3,780 900 0.48

Sitka Spruce 1,570,000 10,200 5610 1150 0.40

White Pine 1,240,000 8600 4800 900 0.35

Eastern
880000 8800 3520 1010 0.47
Redcedar

Red Pine 1,630,000 11000 6070 1210 0.46

Cottonwood 1,100,000 6800 4020 790 0.34

Red Oak 2,200,000 13400 6540 1850 0.54

Red Maple 2,200,000 13400 6540 1850 0.54

White Oak 1,030,000 10300 6060 1820 0.64

Black Walnut 1,680,000 14600 1010 1370 0.55

Figure 5. Bending of a wood beam.

4. Moisture Content

The moisture content of wood also is an important parameter influencing almost all mechanical
properties. Strength properties of wood increase with its decreasing moisture content. For
example, air-dried wood with average moisture content of 12-13 percent will have higher
strength properties than that of wood with 20 percent moisture content. In general, wood is dried
to 15-20 percent moisture for typical structural application rather than using it in green condition.
Strength properties of wood also can be estimated using the following equation for given
moisture content, so that wood can be used with a higher efficiency for any applications:

P = P12 (P12 / Pg) (12-M / Mp–12)

Where:

P = property value

P12 = property value at 12 percent moisture content

Pg = property value at green moisture content

M = moisture content

Mp = moisture content at which property is changed (Mp is assumed 25 percent for most
species, based on USDA Forest Service, 1999).

Example: If a Douglas Fir beam has MOR values of 7,700 psi at green moisture content and
12,400 psi at 12 percent air-dry conditions, its MOR value at 18 percent moisture content can be
calculated as below:

P = 12,400 (12,400 / 7,700) (-6 / 13)

P = 12,400 x 1.610 -0.461

P = 12,400 / (1.610) 0.461

P = 9,959 psi

References:

Detailed information about mechanical properties of wood and wood products also can be found
in the following literature:
Wood Handbook (1999). Wood as an engineering material. USDA Forest Products Lab:
Madison, Wisconsin.

Hoadley, B. (2000). Understanding Wood. The Taunton Press: Newtown, Connecticut.

Ambsore, J. (1994). Simplified Design of Wood Structures. John Wiley & Sons, Incorporated:
New York.

Smith, I., Landis, E., & Gong, M. (2003). Fracture and Fatigue in Wood. John Wiley & Sons,
Incorporated: New York.

Bowyer, J., Smulsky, R., & Haygreen, J. (2007). Forest Products & Wood Science, An
Introduction. Blackwell Publishing Incorporated: Malden, Massachusetts.

SalimHiziroglu
FAPC Wood Products Specialist
 Types of Defects in Timber as a Construction Material
There are various types of defects in timber as a construction material. These defects in timber
can be due to natural forces, fungi, insects, and during seasoning and conversion. Types of these
defects in wood are discussed in detail. Trees give us the timber, which is converted into the
required form and finally used. Before reaching this final stage, timber comes across many
critical stages like growing without defects, cutting at the right time, seasoning, converting, and
using. Different types of defects occur in timber at these various stages.

In general, the defects in timber are mainly due to:

1. Natural forces

2. Fungi

3. During Seasoning

4. During conversion

5. Insects

Defects in timber due to Natural Forces

1. Wind cracks

2. Shakes

3. Twisted fibers

4. Upsets

5. Rind galls

6. Burls

7. Water stain

8. Chemical stain

9. Deadwood

10. Knots

11. Coarse grain

 12. Foxiness

13. Druxiness

14. Callus

1. Wind Cracks in Timber

If the wood is exposed continuously to the high-speed winds, the outer surface shrinks and forms
crack externally, which are called wind cracks.

Fig 1- Wind cracks

2. Shakes in Timber

Shakes are nothing but cracks which separate the wood fibers partly or completely. Different
shakes are formed in different conditions as follows:

• Cup shakes are formed due to the non-uniform growth of a tree or excessive bending by
cyclones or winds. In this case, the shakes develop between annual rings and separate
them partly.

• Heart shakes, the other type of shakes which develop in maturity approaching trees
whose inner part is under shrinkage. The shake spread from pith to sapwood following
the directions of medullary rays.

• Ring shakes are similar to cup shakes, but they completely separate the annual rings.

• Star shakes are formed due to extreme heat or severe frost action. They develop wider
cracks on the outside of timber from bark to the sapwood.

• Radial shakes are developed radially from pith to the bark.

 Fig 2- Shakes

3. Twisted Fibers in Timbers

When the tree in its younger age is exposed to high-speed winds, the fibers of wood gets twisted.
This type of wood is not suitable for sawing. So, this can be used for making poles, posts, etc.,

Fig 3 – Twisted Fibres

4. Upsets

Upsets, a defect of timber in which the fibers of the wood are crushed and compressed by fast
blowing winds or inappropriate chopping of trees.
Fig 4 - Upsets

5. Rind Galls

Rind galls are curved swellings of trees which are formed at a point where a branch of the tress is
improperly removed or fell down

Fig 5 – Ring galls

6. Burls

Burls are uneven projections on the body of the tree during its growth. These are mainly due to
the effect of shocks and injuries received by the tree during its young age.

Fig 6 - Blurs
7. Water Stain

When the wood is in contact with water for some time, the water will damage the color of the
wood and forms a stain on its surface. This defect is called as water stain.

Fig 8 – Water Stain

8. Chemical Stain

Chemical stain is formed on the wood by the action of any external chemical agents like reaction
by the gases present in the atmosphere etc. The stain area gets discolored in this defect.

Fig 8 – Chemical Stain

9. Dead Wood

The wood obtained from the cutting of the dead tree is light in weight and is actually defected.

It is reddish in color and its strength is low.

Fig 9 – Dead Wood

10. Knots in Timber

The central part or stem of a tree is majorly used in the conversion of timber. Branches from the
stem are removed, and the whole rounded stem is taken. But the base of branches forms a mark
on the stem, which results in dark-colored stains on the surface after conversion. This dark-
colored stains are due to the continuity of wood fibers. These dark-colored rings are known as
knots.

Fig 10 - Knots

11. Coarse Grain Defect in Timber

The age of a tree can be known by the number of annual rings. For fast-growing trees, the gap
between the annual rings is very large. This type of tree is called as coarse-grained tress, and
timber obtained from them has low strength.
Fig 11 – Course grain defect

12. Timber Foxiness

When the timber is stored without proper ventilation, the trees growing near the banks of water
bodies and over matured trees may exhibit this type of defect. Foxiness is generally indicated by
red or yellow spots

Fig 12 - Foxiness

13. Druxiness

Druxiness is a defect of timber in which the top surface of timber indicates white spots.

These spots will give the access to fungi.

Fig 13- Druxiness

14. Callus

The wound of the tree is covered by soft skin, which is called a callus.

Fig 14 - Callus

Defects in timber due to Fungi

1. Dry rot

2. Wet rot

3. Brown rot

4. White rot

5. Blue stain
 6. Heart rot

7. Sap stain

1. Dry Rot in Timber

Dry rot is caused by a certain type of fungi that eats wood for their living. They make food by
converting timber into dry powder form. This occurs mainly when there is no ventilation of air or
if the wood improperly seasoned. Absence of sunlight, dampness, presence of sap will increase
the growth of dry rot, causing fungi. This can be prevented by using well-seasoned wood and
also by painting the timber surface with copper sulfate.

Fig 1 – Dry Rot

2. Wet Rot in Timber

Wet rot is caused by fungi that decompose the timber and convert it into a grayish-brown powder
form. Wet rot causing fungi growths mainly when there are alternate dry and wet conditions of
timber.
Fig 2 – Wet rot

3. Brown Rot in Timber

The cellulose compounds of the wood are consumed by certain types of fungi, which then makes
the wood brownish, and this defect is called brown rot.

Fig 3 – Brown Rot

4. White Rot in Timber

Some types of fungi attack lignin of timber and leaves cellulose compounds; hence the wood will
turn into white color, which is called white rot.
Fig 4 – White Rot

5. Blue Stain in Timber

Blue stain is a defect caused by some kind of fungi, which makes the timber bluish

Fig 5 – Blue Stain

6. Heart Rot in Timber

Heart rot is generated in the trees when fungi attack the heartwood through its newly formed
branch. This type of fungi makes the tree hollow by consuming heartwood. This defect is known
as heart rot.

Fig 6 – Heart Rot

7. Sap Stain in Timber

When the moisture content in the timber is more than 25%, some types of fungi attack the
sapwood and make it discolored. This type of defect is known as a sap stain.

Fig 7 – Sap Stain

Defects in Timber During Seasoning

1. Bow

2. Cup

3. Check

4. Split

5. Twist

6. Honeycombing

7. Case hardening

8. Collapse

9. Warp

10. Radial shakes

1. Bow

When the converted timber is stored for a longer time, some timber planks may have a curve
along its length, which is known as Bow.

Fig1 - Bow

2. Cup

If the timber planks curve along its width, then it is called Cupping of timber.

Fig 2 - Cup

3. Check

Check is the formation of a crack in the wood, which will separate the wood fibers. They form
due to over seasoning of timber.
Fig 3 - Checks

4. Split

Split forms when a check extends from one end to the other end, which will split the wood into

Fig 4 - Split

5. Twist

Twist forms when the timber piece is distorted spirally along its length. It looks like a propeller
blade after twisting.

Fig 4 - Twists

6. Honeycombing

Honey combing occurs in the inner part of the timber, which cannot be identified by just seeing.
It is mainly due to stresses developed during the drying of timber.
Fig 6 - Honeycombing

7. Case Hardening

Case is nothing but the top surface of wood, which dries rapidly during seasoning, but the inner
part didn’t. Then this defect is called as case hardening.

Fig 7 – Case Hardening

8. Collapse

During drying, some parts of the wood may dry rapidly while some may not. Because of this,
improper drying shrinkage of wood occurs, that results in the defect called collapse.
Fig 8 - Collapse

9. Warp

Warping is the loss of shape of wood due to stresses developed during drying. Cupping bowing,
twisting of wood come under warping.

Fig 9 - Warping

10. Radial Shakes

Radial shakes develop after the tree being felled down and exposed to the sun for seasoning. In
this case, the cracks run radially from bark to the pith through annual rings.
Fig 10 – Radial Shakes

Defects in Timber During Conversion

1. Diagonal grain

2. Torn grain

3. Chip mark

4. Wane

1. Diagonal Grain Defect in Timber

During the conversion of timber, different cutting saws are used. The cutting should be done
properly. If there is any improper cutting by the saw, then a diagonal grains will appear.

Fig 1 – Diagonal grains

2. Torn Grain

In the conversion, many tools are used. If any of the tools or any other heavy things are dropped
accidentally on the finished surface of timber it will cause small depression, which is called torn
grain.

Fig 2 – Torn Grain

3. Chip Mark

When the timber is cut through the planning machine, the parts of the machine may form chip
marks on it. Usually, they are indicated by chips on the finished surface.

Fig 3 – Chip Mark

4. Wane

The edge part of the timber log contains a rounded edge on one side because of its original
rounded surface. This rounded edge is called wane.
Fig 4 - Wane

Defects in timber due to Insects

1. Termites

2. Beetles

3. Marine borers

1. Termites in Timber

Termites also known as white ants which form a colony inside the timber and eat the core part of
the timber rapidly. They do not disturb the outer layer of timber, so one cannot identify their
presence. The trees in tropical and sub-tropical regions are mostly affected by these termites.
However, some trees like teak, Sal, etc. cannot be attacked by termites because of the presence of
termite preventing chemicals in their cellulose part.

Fig 1 – Termites in timber

2. Beetles in Timber

Beetles are a type of insects that destroy the sapwood of the tree and make a tunnel-like hole
from the bark. Usually, the diameter of the hole is around 2 mm. They convert sapwood into
powder form, and larvae of these beetles use these holes. Almost all hardwood trees can be prone
to damage by these beetles.

Fig 2 – Beetles in timber

3. Marine Borers in Timber

Marine borers are found near coastal areas. They do not consume wood, but they make large
holes of diameter up to 25mm in the timber to live inside it. They excavated up to 60mm deep in
the wood. The wood attacked by marine borers is of less strength and discolored. They can attack
all types of trees present in their region.

Fig 3 – Marine borers in timber

 GRADING OF TIMBER
How Is Timber Graded?

Any timber that is to be used in construction must be graded in terms of its strength and stiffness.
Timber grading is a process through which timbers with similar structural properties are sorted
into different groupings. Though there are, naturally, significant overlaps in properties in the
groups, there are still noticeable and verified differences which can make some types more
suitable for certain tasks than others.

Timber varieties

When timber is to be used within the construction industry, it must be suitable for the project’s
end use. The two main types of timber that tend to be used in construction work are kiln dried
timber and unseasoned timber, due to their respective qualities which lend themselves to
construction work.

Some developers or project workers favour softwood timber, though, on account of its
environmentally friendly aspects, such as its status as a renewable resource, its low carbon
footprint due to its ease of production and its major potential for re-use or recycling at the end of
its life.

Timber grading process

The timber grading procedure can be carried out in a variety of ways, including:

• Visual stress grading

• Machine stress grading

• Machine proof grading

1. Machine grading

The process, when machine graded, is a lengthy one, with the timber needing to meet various
requirements and pass various tests. When it has passed the tests, the timber is then given a grade
stamp which identifies the following facts about the timber:

• Grade

• Producer

• Identification number

• Condition

2. Visual grading

This same stamp will be used when visual grading takes place, with each piece of timber needing
a stamp to be marked onto the timber to notify anyone coming into contact with it or planning to
use it such as a user or inspector to assess its quality.
 Preservation of Timber and Wood.
Any treatment of mine timber for the purpose of extending the useful life of the timber. Various
preservatives are used, such as creosote, zinc chloride, sodium fluoride, and other chemicals.

Preservation of timber is carried out to increase the life of timber. Preservation is done using
different types of preservatives. Methods and different materials used for preservation of timber
is discussed. Increasing life makes timber more durable and it can be used for longer periods.
Preservation also helps the timber to get rid of insects and fungi etc. If preservation is not done,
then wood will be diseased and damaged badly as shown in figure below.

Fig 1 – Untreated Timber

A Preservative is defined as a chemical compound that when used on or injected into the timber
makes the timber ‘poisonous’ for insects and fungi without effecting the structural properties of
wood and timber.

All the wood preserving chemicals are classed under three groups :

(i) The Oil-Soluble Salts. Such compounds are soluble only in oils. The most commonly used
wood-preservative coal tar creosote oil belongs to this category.

It is obtained by destructive distillation of coal.

Following are important qualities of this preservative:

1. It has a high degree of permanence, i.e., it stays within the cells for quite a long time.

2. It penetrates quickly and easily into the wood tissue.

3. It is highly destructive for “fungi.”

Among the negative properties of coal tar Creosote preservative, the most important is its
unpleasant appearance.

Moreover, it does not paint over it. Further, it has a bad smell.

Hence it finds a use for preserving timber parts that are external to the living rooms.

(ii) The Water-Soluble Salts. Such salts make an easy solution with water. There is an
advantage in it. They can be easily dissolved and used.

But there is a disadvantage too. These can be easily “washed away” if the timber happens to be
in moist condition.

Among the water-soluble salts are included: zinc chloride, copper sulfate, sodium fluoride,
sodium fluosilicates, sodium dintrophenoxide, and compounds of arsenic.

(iii) Volatile base salts are those which make solutions with substances like petroleum. The
creosote petroleum blends are the typical example of this category.

Different Types of Preservatives for Timber

• Coal tar

• ASCU

• Chemical slats

• Oil paints

• Solignum paints

• Creosote oil
 1. Coal Tar for Preservation of Timber

Coal tar is heated and obtained liquid hot tar is applied on timber surface using brush. Coal tar
contains unpleasant smell and does not allow paint on it. So, it is used for door frames, window
frames etc. It is very cheap and has good fire resistance.

Fig 1 – Coal Tar

2. ASCU Preservative for Timber

ASCU is a special preservative which is available in powder form. It is dissolved in water to get
preservative solution. It should be added 6 parts by weight of ASCU in 100 parts by weight of
water. The final solution is applied on timber by spraying. This solution does not contain any
odor. It is useful mainly to get rid of from white ants. ASCU contains hydrated arsenic pent
oxide, copper sulphate or blue vitriol and sodium dichromate or potassium dichromate in it. After
applying ASCU, the timber can be coated with paint, varnished etc.
 3. Chemical Slats for Preservation of Timber

Chemical salts like copper sulphate, mercury chloride and zinc chloride are used as preservative
which can be dissolved in water to get liquid solution. They are odorless and do not generate
flames when contact with fire.

Fig 2 – Chemical Slates

4. Oil Paints Preservatives for Timber

Oil paints are suitable for well-seasoned wood. They are generally applied in 2 or 3 coats. Oil
paints prevents timber from moisture. If timber is not seasoned, then oil paints may lead to decay
of timber by confining sap.

5. Solignum Paints for Preservation of Timber

Solignum paints are applied in hot condition using brush. They are well suitable for preserving
timber from white ants. Solignum paints can be used by adding color pigments so, the timber has
good appearance.
Fig 3 -Solignum Paints

6. Creosote Oil for Preservation of Timber

Creosote oil is prepared by the distillation of tar. It is black or brown in color. It contains
unpleasant smell. It is applied in a special manner. Firstly, the timber is well seasoned and dried.
Then, it is placed in airtight chamber and inside air is pumped out. Finally creosote oil is pumped
into the chamber with high pressure about 0.7 to 1 N/mm2 at a temperature of 50oC. After
allowing it for 2 hours, the timber absorbs creosote oil sufficiently and taken out from the
chamber. Creosote oil is flammable so, it is not used for timber works in fireplaces. It is
generally used for wood piles, poles, railway sleepers etc.

Fig 4 – Creosote Oil

Methods of Timber Preservation

• Brushing
 • Spraying

• Injecting under pressure

• Dipping and stepping

• Charring

• Hot and cold open tank treatment

1. Brushing of Timber Preservatives

Brushings the simplest method of applying preservatives. For well-seasoned timber, oil type
preservatives are applied with good quality brushes. For better results, the applied preservative
should in hot condition. Multiple coats should be applied and certain time interval should be
maintained between successive coats.

Fig 1 - Brushing

2. Spraying of Timber Preservatives

Spraying is an effective technique than brushing. In this case, preservative solution is sprayed on
to the surface using spray gun. It is time saving and quite effective.
 Fig 2 - Spraying

3. Preservative Injecting Under Pressure

The preservative is injected into the timber under high pressure conditions. Generally, creosote
oil is applied in this manner which is already discussed above. It is costly treatment process and
required special treatment plant.

Fig 3 – Injection under Pressure

4. Dipping and Stepping Method of Timber Preservation

Dipping is another type of preserving in which, timber is dipped directly in the preservative
solution. Hence, the solution penetrates the timber better than the case of brushing or spraying. In
Some case, the stepping or wetting of timber with preservative solution is allowed for few days
or weeks which is also quite effective process.
Fig 4 – Dipping and Stepping method

5. Charring Method of Timber Preservation

Charring is nothing but burning of timber surface, which is quite an old method of preservation
of timber. In this method, the timber surface is wetted for 30 minutes and burnt up to a depth of
15mm from top surface. The burnt surface protects the inner timber from white ants, fungi, etc.
This method is not suitable for exterior wood works so, it is applied for wood fencing pole
telephone pole bottoms etc.

Fig 5 – Charring Method

6. Hot and Cold Open Tank Treatment of Timber

In this method, the timber is placed in an open tank which contains preservative solution. This
solution is then heated for few hours at 85 to 95 degree Celsius. Then, the solution is allowed to
cool and timber gets submerged with this gradual cooling. This type of treatment is generally
done for sap wood.

Fig 6 – Hot and Cold Open Tank Treatment

7. Termite Shields.

The base of major timber columns may be preserved against organic attack by constructing a
suitable barrier between the timber and the ground.

These barriers of proper design and shape are called termite shields

Properties of Good Preservative for Timber

The preservative used to protect the timber should contain following requirements or properties.

• It should be effortlessly and cheaply available.

• It should not contain any harmful substances, gases etc.

• It should cover larger area with small quantity. Hence, it should be economical.

• Decorative treatment or any surface treatment should be allowed on timber after the
application of preservative.

• Strength of timber should not be affected by the preservative.

• It should not contain any unpleasant smell.

• It should not get affected by light, heat, water etc.

• It should not get affected by fungi, insects etc. and should also efficient to kill them.
• It should not generate flame when contacts with fire.

• It should not corrode metals when it makes a contact with them.

• The depth of penetration of preservative in wood fibers should be minimum 6mm to

25mm.

•
 Quality Tests and Procedures.
Timber is wood suitable for construction purposes. In order to find the quality and sustainability
of the Timbers, Various Quality tests are performed.

They are natural polymeric material that nearly does not age. Moreover, the structure of the
wood ensures efficient strength and load capacity.
Wood can be split into two classes. They are natural and man-made. Hence some examples of
man-made timber are plywood, fibreboard, impregnated wood, etc.

PROPERTIES OF GOOD QUALITY TIMBER

The timber should posses the following qualities.

• It should have a good uniform dark colour.

• Timber should be free from defects such as shakes, flaws, dead knots, etc.

• It should possess regular annual rings.

• The freshly carved surface of the wood should have a sweet smell.

• Moreover, It should have a heavyweight.

• The cellular tissue and fibres should be compact and hard.

• A good timber should be durable and possess elasticity.

• It should be resistant to fungus, insect, etc.

• Also, timbers with compact texture have good resistance to fire.

• It should be inert from mechanical, chemical and physical agencies.

• A good quality wood should hold loads from structures.

qualities of good timber
 TESTS ON TIMBER
In order to find the quality and sustainability of the Timbers, Various Quality tests are
performed. Some of these tests include

• Moisture content test

• Tensile strength test

• Compressive strength test

• Shear strength test

• Bending test

1. MOISTURE CONTENT TEST OF TIMBER

This test determines the moisture content in wood. However, wood contains a small amount of
moisture content. A weighing machine and a drying oven are important apparatus for the water
absorption test.

Fig 1 - Moisture content test of timber

Test procedure

• Initially, Take the specimen with a size of 5cm x 5cm x 2.4cm.

• Then using a weighing machine weigh the specimen. Mark it as W1.

 • After that oven-dry the timber at a temperature of 103-degree celsius.

• Later, take out the specimen when becomes dry.

• Again weigh and mark the weight of the dry specimen as W2.

• Finally, calculate the percentage of moisture content by % of moisture content =

Weight of moisture in sample/ Dry weight of sample = (W1 – W2)/ W2

2. TENSILE STRENGTH TEST OF TIMBER

The tensile strength test defines the strength and ability to withstand breaking. Also, we can
determine the load-carrying capacity of the wood.

Test procedure

Fig 2 -Tensile test on timber

• Firstly, take a specimen with 5cm x 5cm and 20cm in length.

• Then place the specimen on the base plate of the instrument.

• After that apply load either parallel or perpendicular to the grains.

• Mark the load at which the wood breaks.

• Finally, calculate the tensile strength of the wood.

Tensile strength = Maximum load applied / Cross sectional area

 3. COMPRESSIVE STRENGTH TEST

The compressive strength test defines the crushing strength of the timber. Furthermore, this test
determines the load which the wood can support over a period.

Test procedure

Fig 3 - Compressive test

• Initially, take a specimen with a size of 5cm x 5cm x 20cm.

• Then place the specimen in the compressive testing machine.

• Following this, apply load parallel to the grains.

• The specimen should be free from defects. Gradually increase the load.

• Then note down the load at which the timber breaks.

• Lastly, calculate the compressive strength from the below formula.

Compressive strength = Load at which the specimen breaks/ Total area of the specimen

4. SHEAR STRENGTH TEST

The shear strength is important when timber is used as slabs. The load should be applied parallel
to the grains.

Test procedure
 Fig 4 - Shear test apparatus

• The size of the specimen for shear strength is 5cm x 5cm x6.25 cm.

• Then cut the corner of the specimen.

• Thus it produces failure on 5cm x 5cm surface.

• However, this failure occurs tangentially or radially.

5. BENDING STRENGTH TEST

The Bending strength test is necessary when we use timber as a beam. Through this test, we can
find the modulus of rupture and modulus of elasticity.

Test procedure
 Fig 5 - Bending test on timber

• For this, take a specimen of 5cm x 5cm x 7.5 cm in size

• The specimen should be free from defects and deterioration.

• Then drop a hammer with specific weight from a certain height.

• Thus we get the impact bending.

• Lastly using the load and deflection, calculate bending strength.

 Timber Construction Techniques
In the past, wood construction was limited to residential buildings and small commercial
applications. Mass timber frame construction methods have expanded the type of builds that
wood can be used for. With the strength and size of the larger support beams, builders are
breaking past the barriers to create massive wooden structures.

In 2019, the University of Arkansas unveiled the largest mass timbered building in the United
States, containing an impressive 202,027 square feet of interior space.

But builders aren’t only excited about the added structural strength that wood provides:

• Mass timber construction is also much faster, reducing build times by approximately
25% compared to steel and concrete buildings.

• Wood is much more aesthetically pleasing than steel and concrete, making buildings look
better too.

Wood isn’t just for residential buildings anymore. New mass timber frame building techniques
allow even large commercial buildings to reap the benefits of wood construction.

Mass Timber Framing Techniques

Mass timber building techniques are different from traditional timber framing. Instead of using
two-by-four pieces of wood cut on-site, mass timbers are created and cut in a factory before
being shipped to the construction site.

1. Lap Jointing

When they arrive, they’re pre-cut and ready to fit together using lap jointing, which is: A process
that involves cutting precise chunks (joints) out of two pieces of wood so the two pieces fit
together snugly – or mortise and tenon joint – connecting two pieces of wood at right angles by
cutting a notch in one and narrowing the other so it fits in the notch.

All the pieces are then fitted together precisely according to the chosen framing technique.
Below are just a few of the following mass timber frame construction techniques that builders
are using to create impressive commercial and residential structures.
 2. Platform Systems

Platform systems are when each floor of a structure is framed separately and built on top of one
another.

Each floor contains:

• Only load-bearing mass timber beams to hold up the floor above it.

• Once the structure on the bottom floor is completed, it creates a “platform” on which the
next level is framed.

This type of construction technique is mostly used for residential buildings with fewer floors.

3. Balloon Systems

Balloon systems take a vertical approach to mass timber construction.

Instead of framing one floor at a time, construction timbers are:

1. Placed vertically, typically spanning at least two stories.

2. Each floor is then built off a ledge from the vertical supports.

3. If more floors are needed, new vertical beams are placed on top of the existing ones with
the wood grains aligned for additional strength.

Balloon systems are most common in larger industrial or commercial applications because of the
height they allow.

4. Massive Timber Panel Wall Systems

Instead of using individual support beams to hold up the floors – like most other construction
methods – this technique uses load-bearing walls made of mass timbers as the main structural
component (as the name suggests).

What are some key differentiators of massive timber panel wall systems?

• This building technique is similar to using structural insulated panels, except without the
middle insulation layer.

• The structural walls are made entirely of mass timbers.

 • These buildings are very compartmentalized with many rooms and typically used in
residential applications.

Due to the lack of an open floor plan, buildings with massive timber panel wall systems need to
have a detailed layout before construction. Once the building is complete, it’s very difficult to
change.

5. Post And Beam Systems

Post and beam systems are the opposite of massive timber panel wall systems. Instead of walls,
they use huge load-bearing vertical posts that support long horizontal beams.

A significant benefit of this technique:

• Due to the strength of mass timbers, posts can be spread far apart, allowing for immense
open floor plans with no load-bearing walls at all.

This construction technique is popular in commercial applications and is gaining popularity in

residential constructions because of the floorplan possibilities.

6. Hybrid Systems

Hybrid systems aren’t restrained to any building material or construction technique. They use
wood, concrete, and steel together, taking advantage of the benefits of each. Many hybrid
buildings are half steel and half timber construction to benefit from the rigidity of the steel with
the strength and aesthetics of wood.
 Timber Conversion Methods
Timber conversion is the process by which tree trunks (or logs) are cut to suit the requirements
for joinery and for carpentry

Through and through – This is the simplest and cheapest way to convert wood with very little
wastage. Approximately two-thirds of the boards will be tangential (see below) and one third
(the middle boards) will be radial (see below). The majority of boards produced in this way are
prone to a large amount of shrinkage and distortion.

Fig 1 – Through and through Method

Tangential – This method of conversion is used for floor joists and beams since it produces the
strongest timber. It is also used for decorative purposes on woods that have distinctive annual
rings, because it produces crown figuring (see below), also known as flame figuring or fiery
grain, showing as arched top features on the face of the board.
Fig 2 – Tangential Method

Quarter sawn – This is the most expensive method of conversion because it produces the best
quality wood and is ideal for joinery purposes. This is because the boards are radial sawn and
have very little tendency to shrink or distort. In timber where the medullary rays are prominent
such as oak, the board will have a silver-figured (see below) finish; other timbers with
interlocking grain, such as African Mahogany, will show a stripe or ribbon figure (see below).

Fig 3 – Quarter Sawn Method

Boxed heart – When the heart of the tree is rotten or badly shaken, the heart may be boxed in to
keep the defect within the section. Both quarter sawn and tangential timber may be produced
using this method.
Fig 4 – Box Heart Method

• Tangential cut: Wood is converted so that the annual rings meet the wider surface of the
wood over at least half its width at an angle of less than 45°.

• Radial cut: Wood is converted so that the annual rings meet the wider surface of the
wood throughout its width at an angle of 45° or more.

• Crown figure: Distinctive annual rings (e.g. pitch pine and Douglas fir) showing as
arched-top features on the face of the board
• Silver-figure: Where the medullary rays are prominent such as in oak.

• Ribbon figure: Where the interlocking grain such as in African mahogany will show a
stripe or ribbon figure.