Wednesday, April 27, 2011

Estimation of Wastage if Timber

In conversion of timber there is a great wastage.When a log is sawn only 50 to 65 percent can be useful other is waste.Following are the approximate estimation of wastage

Side slabs and trimmings--18%
Saw dust--12%
Loss of moisture--5%

Pressure Process of Applying Preservative

Pressure process is one of the most efficient process in applying preservative. It is of two kinds.

1.Full cell process:In this process cells of wood tissues are desired to practically completely filled with preservative.Woods are loaded on a special kind of trolly and then put in autoclave machine.The vacuum is applied inside the autoclave to remove air from wood as much as possible.Then heated(generally 210 degree Fahrenheit) preservative is pumped in the autoclave with 125 to 200 psi pressure.

2.Empty cell process:In this process preservative forms merely a thin layer on wood cells.All the process is same with full cell process, except that before applying preservative 50 to 75 psi pressure is created to fill wood cells with air and then preservatives are added with about 200 psi pressure.

Different Types of Mortar

1.Lime Mortar- Lime+sand+water
2.Surki(broken brick) mortar- Lime+broken brick+water
3.Lime surki mortar- Lime+sand+broken brick+ware
4.Cement mortar- Cement+sand+water
5.Mud mortar- Mud+water+saw dust(or rice husk or cow dung).


Mortar is the paste obtained from mixing water with cementing or binding material(cement or lime) and an inert material(sand or broken brick or stone).

Functions of Various Ingredients of Cement

1.Lime:It is very important in cement.It forms about 63 percent of cement. The nature of cement depends on it.Defeciency in lime reduces the strength of cement and cause it to set quickly. Again excess cause cement unsound and cause disintegration and expantion.

2.Silica:It is another important compound. It imparts strength to concrete.

3.Alumina:It imparts quick setting property of cement. Clinkering temperature is lowered by adding of alumina.

4.Magnesia:It should not present in cement more than 2 percent.Excess reduce strength.

5.Iron oxide:It imparts the color of cement. At high temperature it goes to a chemical reaction with calcium and aluminium and forms tetracalcium aluminofferrite which imparts hardness and strength.

6.Salphur tri oxide:It should not present more than 2 percent.Excess cause cement to be unsound.

7.Calcium sulphate:It is present in cement in the form of gypsum.It retards the setting of cement.

8.Alkalies: It should not present more than 1 percent.Excess cause efflorescence.

Differences Between Thermoplastic and Thermosettingplastic

     Thermoplastic                                      Thermosettingplastic
1.These are plastics which can          1.These are plastics which harden permanently.
be softened after once hardened        can not be reshaped once hardened.
and again can be hardened
2.Retains almost all the original         2.Properties especially chemical properties changes
properties remelting and then            after remelting
3.e.g.Nylon, poly vinyl chloride,          3.e.g. Phenol formaldehyde, urea
cellulose acetate etc.                         formaldehyde etc

Differences Between Sapwood and Heartwood

       Sapwood                                                Heartwood
1.It is the living element of           1.It is the dead element of tree.
2.It is comparatively weak.           2.It is comparatively strong.
3.It is more in young trees.          3.It is more in old trees.
4.Contains higher moisture.        4.Contains less moisture.
5.Lighter in color                         5.Darker in color.
6.Has weaker cell wall.                6.Has weaker cell wall.
7.Attracts fungus and insects      7.Does not attract fungus and insects.

Saturday, April 23, 2011

The Essential Properties of Preservatives of Wood

1.It should be safe in handling and use.
2.Non injurious to wood tissues and do not react with them.
3.Should not get washed away and permanently preserve.
4.Should be such that decorative and ornamental paints could be applied on wood.
5.Should be non flamable.
6.Penetrate thorough timber.

Market Forms of Timber

The followings are the various types of market forms of timber.
1.Log     2.Lumber     3.Bilk     4.Deal     5.Batten     6.Plank     7.Board     8.Scantline     9.Pole

Conversion of Timber

The preparation of timber from felled tree by cutting off branches, removing bark., cutting and sawing to convert it to marketable form is termed as conversion of timber.

Ply wood

Plywood consists of number of thin sheets of wood(veneer) which are pressed and bonded together by some bonding materials like glue or synthetic adhesive under temperature of 350 degree Fahrenheit to 500 degree Fahrenheit.The grains of each sheet are bonded right angles to each other to uniform strength in both direction and reduce shrinkage.Plywood is relatively lighter then other plank of same strength. Sometimes plywood is covered with plastic sheet for attractive appearance, zero water absorbance, reduction of decay etc. Plywood is specially used where some amount of bending is necessary. Generally not less then three sheets of woods are used for plywood.


Veneers are thin layers of wood of 1/16 to 1/ 4 inches..It is used when lightness, stiffness, durability, no-shrinkability, non-splitting and decorative properties are desired, Veneers are generally obtained from those woods which have well shaped grans and pleasing appearance. Veneers are used in mainly manufacturing plywood, batten boards, decorative facings and laminating boards.

Bulking of Aggregate

The increase of volume of given weight of aggregate due to the presence of moisture is called bulking of aggregates.5 to 8 percent of moisture of aggregate weight cause 20 to 30 percent volume increase. This because of the creation of thin film of water inside aggregates which cause interlocking air.This air tries to get out and cause volume to adding of water in dry aggregates the volume increase up to adding of 8 percent of water of aggregate weight.Further adding of water cause water to move into the void of aggregate particle. This cause volume to decrease.When aggregates are saturated its volume is same as the dry condition.Fine aggregates increase volume more than coarse aggregates.

The bulking is determined by following expression
                    bulking, b=(Vm/Vd)*100
Where Vm is the volume with moisture and Vd is the dry or fully saturated volume and b is the bulking percentage.