Timber-It is a wood which is utilised as a building material in the construction or for another engineering purposes.
Timber Top 5 defects details
Introduction to timber
In general, timber is taken from the trunk of a tree. All over the world, there are many varieties of these trees.
Approximately 1/5th of the world land surface is occupied by this timber trees.
Though it possesses precious properties like small bulk density, low heat conductivity, high strength etc, it has its disadvantages like inflammation, susceptibility to decay, irregularities in properties due to fluctuations in moisture content, changes in strength etc.
The connection with timber the following three words to be noted Rough, converted, Standing types.
Rought: The wood which is received after dropping from a tree is indicated by this term.
Standing: The alive tree comprising of timber is indicated by this term.
Converted: The sawn wood which is divided into different sizes for commercial purposes is indicated by this term
Alive trees are classified into endogeneous and exogeneous.
Endogeneous trees: If the trees grow inbound and pulpy mass is seen in their longitudinal segments, such trees are indicated by this term. Palm trees, cane, bamboo trees are examples of this type.
Exogeneous trees: If the trees spread outwards with an increment in bulk and forming separate serial rings in horizontal directions, such trees are indicated by this term.
These trees are again classified into deciduous, conifers trees.
Deciduous trees: Broadleaf trees are indicated by this term. These leaves befall in autumn and new leaves arise in the spring season.
Hardwood is generated by these trees and they are strong, dark in colour, close-grained, heavy, non-resinous and don’t provide any annual rings. Mahogany, teak, sal wood belong to hardwood type.
Conifers trees: Evergreen trees are indicated by this term.Till the fresh leaves grow, old leaves won’t fall.
Softwood is generated by these trees and they are lightweight, resinous, week, light coloured and provide annual rings. Deodar, pine, fir,chir, Koil, spruce etc belong to softwood type.
For engineering works, the timber utilised mostly related to exogenous trees.
The following are the 5 defects:
- Fungal defects
- seasoning defects
- Due to Natural forces
- Due to the conversion of timber
- Due to insect
1. Fungal defects
The fungi which are microscopic plant organisms attack timber when there is the appearance of air, warmness and moisture content higher than 20%.
Due to fungi, the following are the defects:
- Wet rot
- Heart rot
- White rot
- Blue stain
- Sap stain
- Brown rot
- Dry rot
Chemical decomposition of wood is created by different fungi and convert it into greyish-brown powder.
The wet and dry differing conditions help for growing of wet rot.
When unseasoned wood opened to the wind and rain-wet rot can attack.
By using well-seasoned wood for exterior works and by applying paint or by covering wood by tar, wet rot can be prevented.
In this defect, the heartwood will be affected when a breach of the tree exposed to atmospheric agencies.
The bluish colour will be imparted when the sap of wood is attacked by a particular type of fungi is termed as Blue stain defect.
Sap stain is the incomplete decay of wood by a particular type of fungi. This type of defect is termed as Sap stain defect.
The disease or deterioration of timber is designated by the name rot. The blue colour will be imparted the cellulose compounds are eliminated by a particular variety of fungi, hence this defect is termed as brown rot.
This White rot is exactly the reverse of brown rot defect.
When the wood is attacked by the particular type of fungi, it is converted into dry power. This type of defect is called Dry rot.
At areas where free air circulation is not there and in wet regions like toilets, kitchen etc, this type of defect will occur.
This defect can attack the sap woods, sal woods if seasoning not done properly or wood are not stored properly.
By using sap free and well-seasoned timber this type of defect can be restricted.
If the portion of the wood is severely affected by this defect, then the portion which is infected needs to be removed and the surviving part which is not effected can be stopped by painting copper sulphate solution.
2. Seasoning defects
During the process of seasoning, wood can get subsequent defects.
Cup,bow defect,warpage,honey comb,radial shakes etc.
3. Defects due to natural forces
The following are the defects due to natural forces
Rind galls, Shakes, coarse grain, knots, twisted fibres, Druxiness, Burls, Foxiness, Upsets
Gall represent unusual growth, the rind is known as bark. Rind galls are the unusually curved swelling observed on the tree body.
This type is observed rarely and the wood is not long-lasting, become very week in the tree.
Shakes are the cracks which slightly or isolate the fibres of the wood.
The following are the Shake types:
Radial shakes, ring, cup, heart, star shakes
Radial shakes are copious, fine, irregular and comparable to star shakes.
After dropped down when a tree is flashed to the sun for seasoning this shakes can occur.
When the entire ring is overlaid by cup shakes such type is termed as ring shakes.
In the circular area, if the tissues get cracked, such type is termed as cup shakes. From one annual ring to another it slightly separates and the crack will be in a curved shape.
Expansion of cracks from bark towards the sapwood is termed as star shakes.
During the growth period of the trees if heat or frost is severe then star shakes may occur.
The occurrence of cracks at the core of the tree is termed as heart shakes and they spread in medullary rays from pith to sapwood.
When trees grow fast, annular rings get enlarged. Coarse grain wood owns more insufficient strength.
The limbs or branch bases of the tree which are cut off or broken are known as knots.
As the connection of wood fibres separated by knots, they become week.
Wood fibres which are wounded by squeezing or smashing are known as upsets.
Due to exposure to wild blowing trees or abnormal falling of trees, this defect may occur.
This defect symbolises When the pith or centre of the tree is surrounded by reddish-brown or yellow stains.
Due to wild blowing breezes twisting of tender trees may occur and fibres of the wood are twisted in one direction. Such defect is termed as twisted fibres.
Due to a specific type of fungi, white spots are developed and they are covered by healthy woo. Such a defect is termed as Druxiness.
Wen a tree experiences a shock or got wounded, On the body of wood unusual projections arises. Such a defect is termed as Burls.
4. Defects due to the conversion
The timber during the conversion process into commercial sizes, the subsequent defects may happen.
Wanes, diagonal grain, chip mark, torn grain.
On the fabricated piece of timber if the original rounded surface is present, then such defect is termed as wanes.
Due to inappropriate sawing of sapwood, this defect may happen.
On the finished exterior of the wood, if marks or sign set by chips, such defect is termed as Chip mark.
By dropping tools or by other objects, if little depression formed on the surface of wood, such defect is termed as a torn defect.
5. Defects due to insects
In general, The decay of timber is due to the below-mentioned insects.
Marine borers, beetles, termites
These termites are also known as white ants and semi-tropical and tropical countries they observed in excess.
This marine borer does not feed on wood and in general observed in salt waters.
This insects are small and can cause decay of timber rapidly.
Good timber qualities
The quality of wood depends on the subsequent factors.
- Falling time
- Seasoning methods
- Soil nature beneath the tree
- Area environmental conditions
- Preservation process
Good wood requirements
The following are the good wood requirements
- The surface of the wood should be fresh and should have silky lustre.
- Well seasoned and without any original defects.
- should be long-lasting, hard, tough and should not be attacked by fungi, wood rot etc.
- When brought out it should smell sweet and should not break when a nail is pressed into it.
- Must have general annular rings with consistent colour.
Preservation types of timber
To increase the span, durable and protect from attacks of insects, fungi etc wood is applied by using the following preservatives :
- Applying paints like oil paints,solignum paints, creosote oil
- Applying coal tar
- Using chemical salts
- Using Ascu treatment
i. Applying oil paints
With 2 or 3 coats oil paint is coated on the exterior of the wood for preventing it from moisture and to make it more durable.
ii. Applying Creosote oil
The process of applying creosote oil on the interior of wood is also known as Bethel’s or creosoting method and this oil is produced from tar distillation.
This oil is applied to the exterior of wood under high temperature, pressure over 2 hours.
By applying this oil, wood can be protected from the attack of fungi and can make its life span double.
In general poles, railway sleepers, piles adopted this method.
For interior house surfaces, this method should not be practised.
iii. Applying solignum paints
This solignum paint is highly toxic and applied on wood for preventing it from white ants.
iv. Applying Coal tar
Tarring is the process of applying coal tar on the exterior of wood.
v. Using Chemical salts
The waterborne chemical salts like sodium fluoride, copper sulphate, zinc chloride and mercury chloride are practised as preservatives for wood.
These chemical salts are non-inflammable, odour-free and when they apply there will be an increment in weight of wood.
vi. Using Ascu treatment
To prevent from white ants this Ascu solution is used on wood.
This Ascu is obtainable in powder form and its solution is developed by mixing 6 parts of Ascu power with 100 parts of water.
This Ascu compound consists of 4 parts of potassium dichromate, 1 part of Hydrated arsenic pentoxide,3 parts of copper sulphate.
5 Preservation methods
The 5 preservation methods are given below :
- Injecting solution under pressure
- Cold and hot open tank treatment
Using a spraying pistol the preservative solution is applied on the wood surface and this method is more effective than brushing.
The preservative solution is applied to wood by using brushes and in general, this method is adopted for seasoned wood. Before this application crocks should be filled.
Injecting solution under pressure
The areas where the wood is not durable and where there is a possibility of the insects or fungi attack this method is used.
The wood surface is charred and kept wet for 30 minutes and then burnt over a wood fire and then cooled with water.
A coal layer is developed due to burning and this layer protects the wood from fungi, white ants attack.
This charred wood cannot be used for external works as they look black after burning in fire and their strength is also reduced due to the decrease in cross-section during charring.
Cold and hot open tank treatment
The preservative solution is kept in a tank and is heated for a few hours at 85 degrees, then the wood is submerged and the tank then allowed to cool gradually.
By this method, the sapwood can be protected.
Fire resistance of wood
Based on fire resistance of wood, it has two types: Nonrefractory and refractory.
Refractory type wood
Refractory wood does not catch fire easily. Example: Sal, teak belongs to this type.
Non-refractory type wood
Nonrefractory wood easily catches fire. Deodar, chir, fir belongs to this type.
Methods to make wood more fire-resistant
The following methods used to make wood more fire-resistant
Sir Abel’s process, special chemicals applications.
Sir Abel’s process method
By applying a dilute sodium silicate solution, slaked fat lime and concentrated soda silicate on cleaned wood to make it fire-resistant.
Special chemicals application
By application of Special chemical’s like borax solution on wood makes its fire-resistant. This chemical is also called as antipyrine.
Applying these chemicals, wood does not burn even at very high temperature.
Timber seasoning types
Seasoning is done for the following reasons:
- When wood utilised as fuel, to make it burn quickly seasoning is done.
- To minimise the cost of handling, transport by decreasing the weight of wood.
- To decrease shrinkage, cracks and warpage in wood.
- To give strength, hardness and to make electrically resistant.
- To resist the attack of insects, fungi.
- To make it suitable for undergoing treatments of preservatives, paints etc.
The following are the seasoning methods:
Artificial, natural seasoning.
Artificial seasoning methods
Chemical seasoning, Boiling, Kiln, electrical and water seasoning comes under artificial seasoning methods.
Chemical seasoning method
In a solution of suitable salt, wood is submerged and then seasoned in a usual way by bringing out.
In this method, by submerging wood in water and boiling it seasi=oning is done. Strength, the elasticity of wood will be affected by this method.
Inside an oven or airtight container drying of wood is performed in this method.
Uisng high-frequency alternating current, seasoning of wood is done.
This method is fast but is uneconomical due to its huge cost.
By immersing wood in a running stream of water for a period of 2 to 4 weeks and taken out of water.
During this immersing time, sap included in the wood is wiped away by water.
Natural seasoning method
This method is also called air seasoning as the wood is seasoned in natural air.
Advantages of this method
- By this method, skilled supervision is not required and it is simple, cheap.
- Moisture content can be reduced by 10 to 20 % based on climatic conditions.
- For wood sections greater than 100 mm it is not economical to provide artificial seasoning.
Disadvantages of this method
- This method sometimes becomes difficult to control as it depends on natural air.
- There are risks of ends splitting if dense sections of timber are not extended by suitable moistureproofing coating.
- Drying may not be uniform and even at different segments.
The manufacture of timber in the factory by the experimental process is called Industrial timber.
This kind will possess wanted strength, shape and appearance.
5 varieties of industrial wood given below:
- Fibre boards
- Impreg wood
- Comperg wood
The other name of fibre boards are reconstructed or pressed wood.
It is inflexible and prepared by heating the cane, pieces of wood etc and by compressing between steel plates under pressure and the thickness ranges from 3 mm- 12 mm.
These boards are utilised for making tables top, flush doors, heat and sound insulating materials etc.
When the timber partially or fully coated with resins like phenol-formaldehyde, such wood is termed as impreg wood.
Veneers are the superior quality slices or thin sheets of wood and have a thickness between 0.4 mm – 6 mm.
Rosewood, teak, mahogany, Vak, Sisso etc types of timbers are suitable for making veneers and they are utilised for creating lamin boards, batten boards, plywoods.
The making method of compreg is similar to impreg wood beside the curing is carried out under pressure.
Between 1.3 to 1.35 will be the specific gravity of this type of wood.
Ply means thin layers. By grouping three or more veneers above one another with the direction of grains of succeeding layers at right angles to each other and pressure of 0.7 to 1.4 N/mm2 is applied for producing these plywoods.
These plywoods have higher impact resistance to blows than normal wood and they are used for doors, wooden partitions, concrete formwork, ceilings, panelling, railway coaches etc purposes.
The plywood is available as Lamin board, Batten board.
The above specified 5 timber defects, preservation methods, types, seasoning methods are practised and fire-resistive type, industrial timbers are used as building materials or for engineering purposes.