LESSON 1 & 2
TOPIC: TIMBER PROCESSING
At the end of the lesson, you should be able to:
explain key terms and concepts related to timber
processing
describe the properties of good timber
calculate moisture content of timber
identify common timber defects
explain treatments and preservation methods for timber treatment
state the importance of timber treatments
INTRODUCTION
Timber processing involves the following stages:
i. Growth of timber ii. Felling of timber iii. Conversion of timber iv. Seasoning of
timber
v. Preservation of timber
TIMBER GROWTH
Timber is the technical name used for grown trees which can be processed into wood useful for
building construction, carpentry and joinery purposes. The tree produces its food through photosynthesis.
PHOTOSYNTHESIS is the process whereby tree leaves produce their food through their chlorophyll with the
aid of sunlight and air.
FELLING OF TIMBER
Felling of trees involves the use of tools such as chain saw, hand saw or axes to cut down trees. The
most convenient among them is chain saw. Felling of trees is done CROSS SECTIONALLY.
CONVERSION OF TIMBER
After felling, the tree is cut into log and transported to the sawmill. TIMBER CONVERSION is the
process of cutting timber (or logs of wood) with sawing machine into marketable and commercial sizes,
such as planks, boards etc. The conversion center is known as SAWMILL.
Basically, there are three common methods for timber conversion.
i. Plain sawing (through and through or slash cut) ii.
Quarter sawing (Rift sawn) iii. Tangential
sawing
NOTE: Plain sawn is the simplest and most economical method of timber conversion.
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Tangential sawing
IMPORTANCE OF TIMBER CONVERSION
Timber conversion is important because:
a. It allows easy seasoning of timber
b. It makes timber or wood available in marketable and commercial sizes
c. It allows easy usage of timber by crafts men. (carpenters and furniture makers)
SEASONING OF TIMBER
Timber seasoning is the process of reducing or drying out excess water content (moisture) from the
timber or wood. There are two methods of timber seasoning.
1. Air seasoning (Natural seasoning)
2. Kiln seasoning (Artificial seasoning)
AIR SEASONING: This is a method of seasoning whereby natural free air circulation dries timber stacked or
piled under a shade.
KILN SEASONING: This is an artificial method of drying timber or wood. The timber is stacked or piled on a
movable trolley and placed inside a brick oven or kiln which is then closed. The temperature, humidity and
air circulation can be controlled either manually or automatically from outside the kiln.
REASONS FOR TIMBER SEASONING
Timber is seasoned or dried for the following reasons.
a. To make the wood lighter in weight
b. To increase the strength of the wood
c. To make the wood more durable and more stable
d. To make the wood take preservatives more easily
e. To make the wood take paints and polishes more easily.
PROPERTIES OF GOOD TIMBER
1. A good timber must be comparatively light in weight for easy transportation
2. It must have high strength to weight ratio
3. A good timber must be less expensive than other construction materials
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4. A good timber must be an excellent insulator to heat and electricity.
5. It must have a prompt resale value
6. It must be relatively resistant to cold and climatic changes.
MOISTURE CONTENT OF WOOD
Moisture content of wood (M.C) is the weight of moisture expressed as percentage of the dry weight of
timber.
CALCULATION OF MOISTURE CONTENT
1. Cut a small part of the wet wood
2. Weigh the small part of the wet wood cut (Ww)
3. Dry the wet wood in a kiln
4. Weigh the dried wood (Wd)
𝑤𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑤𝑒𝑡 𝑤𝑜𝑜𝑑−𝑤𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑑𝑟𝑦 𝑤𝑜𝑜𝑑
Percentage Moisture content = x 100
𝑤𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑑𝑟𝑦 𝑤𝑜𝑜𝑑
% M.C =
Example: If a sample of wood weighs 100kg before drying ad 60kg after drying, what is the weight of water
in the wood and the percentage moisture content of the wood.
Solution:
Ww=100kg % M.C =
Wd= 60kg % M.C = 66.67%
Weight of water in the wood = 100 – 60 = 40kg
% M.C =
% M.C = x100
Another quick method of determining the moisture content of timber is by using an instrument called
ELECTRIC METER which shows the moisture content on a graduated computerized scale.
CLASS WORK: The weight of wet wood is 100g and after it was dried in a kiln, it weighed 80g. Determine
the weight of water in the wood and the percentage moisture content of the wood.
ASSIGNMENT 1
1. Sketch the following methods of timber conversion : through and through saw, quarter sawn and
tangential sawn
2. Give three differences between Natural and Artificial methods of seasoning.
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COMMON TIMBER DEFECTS
Defects in timber are irregularities or faults which reduce the market or economy value of timber. Timbers
are exposed to different faults but not all defects are bad some gives beauty and interest to the wood
surface.
TYPES OF TIMBER DEFECTS
NATURAL DEFECTS: Natural defects are defects that are associated or happened during timber growth.
They are caused by wind storm, irregular growth e.t.c. Examples are knots, twisted grains, heart shakes,
star shakes, cup-shakes, ring shakes, upset etc e.t.c.
ARTIFICIAL DEFECTS: They are caused and associated with poor conversion and bad seasoning. Examples
are twist, bow, cupping, fungi, stains, insect attack, end split, honey comb, wood worms attack etc.
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TIMBER TREATMENTS AND TIMBER PRESERVATION METHODS
Preservation of timber refers to any process used to prolong the serviceable life of the timber. The
materials used are called preservatives.
TYPES OF TIMBER PRESERVATIVES
1. Preservative oil such as creosote oil, pentachlorophynol in mineral oil, copper Napthenate amongst
others.
2. Water Borne preservative such as Copper Chrome Arsenic, Boron, and fluorine compound amongst
others.
3. Tar: used for undergrounf timber in dampness situation (Electric Poles)
4. Polish
METHODS OF APPLYING PRESERVATIVES
i. Brushing ii.
Spraying iii.
Dipping
iv. Pressure impregnation or pressure treatment
PROPERTIES OF GOOD PRESERVATIVES
1. It must be odourless
2. It must be chemically stable
3. It must be easy to handle
4. It must be easy to apply
5. It must be resistant to fire
6. It must be relatively cheap to buy (affordable)
7. It must be poisonous to destructive agents e.g insects, fungi, wood worms etc.
IMPORTANCE OF TIMBER TREATMENTS
Timber preservation or treatment is important because:
1. It makes timber resistant to weather, fungi and insect attack.
2. It makes timber fire resistant
3. It protects timber from rot and decomposition (decay)
4. It makes timber last longer
5. It makes timber resistant to water especially timber used under water
6. It increases the economic value of timber. Treated timbers are more expensive in the market.
ASSIGNMENT 2
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1. Sketch a cross section of a timber log, identify, label and state the functions of the parts of the
section.
2. Sketch the following timber defects: twisted grain, wane edge, star shake, heart shake, heart shake,
cup shake, ring shake, twisting, bowing and end split.
3. A wood sample weighs 61g, after drying and the quantity of water in the wood is 13g. Calculate the
weight of the wood before drying and the percentage moisture content of the wood. (leave your
answer in 2 D.P).
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