1. Timber Seasoning and Lamination
There are two ways that timber may be seasoned:
• Air Dried Seasoning
• Kiln Dried Seasoning
There are advantages and disadvantages to both methods.
Advantages Disadvantages
Kiln Dried Seasoning The temperature may be monitored and adjusted Because of the machinery needed the
so that the end product is of a higher quality. end product is considerably more expensive.
Bugs and insects are killed during the kiln drying
process.
Air Dried Seasoning The process is inexpensive as it does not require The process is entirely dependent upon the
any machinery. climate. An increased in humidity will result in a
longer process with a lower quality end product.
2. Timber Seasoning and Lamination
Calculations on the percentage moisture content of pre-seasoned
(initial dry weight) and post seasoned (dry weight) timber can
be calculated using the following formula:
Initial dry weight - dry weight
___________________________ X 100
dry weight
If the weight of a piece of pre-seasoned timber is 20 kilos and its
post seasoning weight is 15 kilos then the percentage
moisture content of the timber is 33%.
Caution must be taken when seasoning timber to ensure that
overheating does not occur. If overheating occurs then a form
of case hardening may occur whereby the outer ‘skin’ of the
timber becomes excessively dry and brittle.
The diagram given opposite is of the airflow around a timber kiln.
Air is forced in a circular path around the kiln. As it circulates it
passes across a set of heaters that dry the air.
Because of the potential difference in the moisture content of the
timber and the air circulating around it, moisture is drawn out
of the timber into the air and expelled through vents.
3. Timber Seasoning and Lamination
Timber Lamination
There are three general types of laminated boards:
Laminated boards (lamin board)
Are manufactured boards made up of strips of natural
timber that are between 5 / 7mm in thickness.
Block board
Are manufactured boards made up of strips of natural
timber that are up to 25mm in thickness.
The outer surfaces are clad with a veneer for
decoration and strength purposes.
Plywood
Is a manufactured board made up of layers of natural
timber veneers or laminates that are glued
together. Alternative veneers have their grains
running at right angles to each other leaving the
outside two veneers with the same grain
direction. There is always odd numbers.
The outer surfaces are clad with a veneer for
decoration and strength purposes.
The interlocking structure offers uniform strength,
good dimensional stability and resistance to
splitting.
Epoxy resins may be used to increase the
waterproofing of those plywoods that are to be
used in damp or external situations. These
plywoods include builders form ply and marine
ply.
4. Timber Seasoning and Lamination
Answer the following questions relating to timber seasoning and lamination.
1. Give two advantages that air dried timber seasoning has over kiln dried timber seasoning.
Answer: a) The end product of air dried timber is less expensive.
b) A larger quantity can be processed at any one time.
2. Give two advantages that kiln dried timber has over air seasoned timber.
Answer: a) A greater percentage of moisture can be removed from the timber resulting in a better quality end product
that is less prone to movement.
b) There is less weight in kiln dried timber and this has an impact of and freight
charge that is paid by the kilo.
3. Calculate the percentage moisture content of a piece of unseasoned timber with a weight of 30 kilos that
has a seasoned weight of 22 kilos.
initial weight (30) – dry weight (22)
____________________ x 100 = 36%
dry weight (22)
4. Explain the principal of the potential difference in the moisture of timber held within a kiln and the dried air
circulating around it.
Answer: Because of the homeostasis effect, the timber expels moisture in order to acquire the same moisture content of
the air around it.
5. Timber Seasoning and Lamination
5. Describe the formation of lamin board.
Answer: Lamin board is made up of layers of 5 – 7mm strips of natural timber glued together and veneered.
6. Describe the formation of block board.
Answer: Block board is made up of layers of natural timber up to 25mm in thickness, glued together and
veneered.
7. Offer four distinguishing features of plywood.
Answer: - Plywood is made up of layers of natural timber veneers or laminates glued together.
- Alternative grains run at right angles to each other.
- Plywoods always consists of an odd number of veneers.
- The outside veneers of plywood always have their grains running in the same
direction.
8. What glue might be used in the manufacture of form ply or marine ply?
Answer: Epoxy resins may be used to ensure a higher degree of weatherproofing.
9. Offer two reasons why lamin boards and block boards have their outer surfaces ‘clad’ with a veneer.
- Decoration
- Strength
10.
