Level 1 Term 1 Level 1 Term 2
ARCH 109
BUILDING & FINISH MATERIALS
Ahmed Inzamam Chowdhury Lecturer, Department of Architecture
Daffodil International University
Mortar
Introduction
• Mortar, a bonding agent between building materials, is mainly a mixture
of water, fine aggregate (sand, surki, etc) and binding material like cement , lime etc. The applications of mortar in various construction phase have made it a very important civil engineering material
Some of the numerous functions of mortar in construction are given below.
Mortar is used to bind together the bricks or stones in brick or stone masonry.
It is used to give a soft even bed between different layers of brick or stone masonry for equal distribution of pressure over the bed.
It is used to fill up the spaces between bricks or stones for making walls tight.
It is used in concrete as a matrix.
It is used in plastering works to hide the joints and to improve appearance.
It is used for molding and ornamental purpose.
Mortar mix is a binding material used for construction purposes. The most commonly used mortar ingredients to make different types of mortar are:
Cement Lime Sand Surki Mud Water
For getting a good mortar mix, it is very important to use quality ingredients. Without good ingredients, it is not possible to get the desired quality of mortar mix. The
properties of good mortar ingredients are given below.
Properties of Good Mortar Ingredients
Cement: It should be fresh and free from adulteration. Lime: Lime must be
well slaked.
Sand: Sand should be sharp, angular and porous. It should be free from salts
and other impurities. Read>> Function of Sand in Mortar
Surki: Surki should be perfectly pure and free from foreign matter. It should
be sufficiently fine to pass through No. 8(US) sieve.
Mud: Mud should be free from adulteration.
Water: Water should be clean and free from salts and other impurities.
Precautions Required while Using Mortar Mix
Mortar should be mixed in small quantities so that it can be used
conveniently before the mortar starts setting. The mortar which has set already should never be used. The followings are the maximum time limits for different kinds of mortar:
If mortar contains hydraulic lime (Class A lime) as an ingredient, it shall be used within four (04) hours of grinding.
If mortar contains surki or cinders an ingredient, it shall be used within twenty-four (24) hours of grinding.
In the case of cement mortar, the time limit is 90 minutes after adding water.
Precautions Required while Using Mortar Mix
In masonry construction work, usable bricks or stones should be soaked in water very thoroughly for at least for 12 hours before they are used in work with mortar. It will prevent the absorption of moisture from the mortar
before it sets.
Mortar should not contain excess water. It should be as stiff as it can be used without inconvenience.
Fresh water should be used in mortar mix preparation. The water should be free from oils, dust, alkalies, etc.
Use of seawater in mortar mixture should be avoided.
The joints should be well filled with mortar.
After casting, mortar works should be kept wet for a week or two. It will prevent the rapid drying of mortar, especially in hot weather.
As frosty weather affects the setting of cement, the work should be stopped in frosty weather.
Function of Sand in Mortar
Followings are the functions of sand as one of the ingredients of mortar.
Generally, sand is not used in the mortar to increase its strength. Rather it is mainly used as an inert material to increase the volume of mortar for the economy.
Using sand in the right amount can produce cheap mortar without hampering mortar strength.
Sand subdivides the paste of cementing materials into a thin film which is the basic principle involved in using all cementing materials.
Sand offers the requisite surface area for the film of cementing materials to adhere and to spread.
Function of Sand in Mortar
Sand helps to prevent mortar shrinkage. It also prevents cracking of mortar during setting.
Well-graded sand increases the density of mortar.
Sand allows Carbon-Di-oxide from the atmosphere to reach to some depth in case of ft lime mortars and thereby improves their setting capability.
It is also claimed that some chemical reaction takes place between silica
(SiO2) of sand grains and the constituents of the cementing materials to form a hardened mass.
(Reference: A text Book of Engineering Materials by Dr. M.A. Aziz)
