Concrete
Mortar and Plastering
Mortar is a mixture obtained by mixing sand, (fine aggregate) a binding material (cement/lime) and water in definite proportions.
Need for Mortar
>It is used as a binding material sin bricks and stone masonry.
>It is used to cover the surface of masonry works. (Plastering)
>It is used for pointing purpose (bricks and stone masonry)
>It is used in floor works.
Types of mortar
There are three types of mortars namely cement mortar, lime mortar ans water-proof mortar.
(a) Lime mortar:
>Lime mortar consists of equal volume of lime and sand.
>Fat lime is recommended for plaster work.
>Fat lime contains 75% of calcium oxide and it combines with carbon dioxide at atmosphere and gives calcium carbonate quickly.
>Finely sand generated used for making plaster.
>It should be used within four hours after it is prepared.
(b)Cement Mortar:
>Cement mortar consists of one part of cement to required parts of river sand by volume, depending on the work to be done.
>The cement and sand are mixed on water tight platform and this mortar should be used within 30 minutes after adding water.
(c) Water-proof Mortar
>water proof mortar consists of one part of cement, two part of sand and pulverized alum at the rate of 12 kgm^3 of sand.
Composite mortar: If a mortar is prepared by adding both cement and lime with sand and pulverized alum at the rate of 12 kg/m^3 of sand.
Cement mortar is mixed either manually or with the help of a mechanical mixer. Lime mortar is mixed either manually or by using bullock or power driven mortar grinding mill.
Mortar-mix proportions and uses
|
Cement: Fine aggregate |
Uses |
|
1:8 |
Random rubble masonry |
|
1:6 |
Size stone masonry and Brick (brick work) |
|
1:4 |
Plastering |
|
1:2 or 1:1 |
Pointing |
Plastering
The process of covering the surfaces of masonry, beam or column with mortar is called plastering. Mortar is a substance obtained by mixing sand, a binding material (cement/time) and water in definite proportions plaster may be applied either one, two or three coats and usual proportion is 1 cement and 3 sand, or 1 cement and 5 sand.
Mortar used for plastering
Any one of the following is used.
>Lime mortar.
>Cement mortar.
>Water-proof mortar.
>Usually plastering is in single or double coat.
Need for plastering
>It is done to provide an even surface to wall, beams and columns etc. It protects the surfaces from the action of wind, dust rain etc. It prevents damping of the entire wall, sunshade etc. It hides the defects in work-man ship.
Stages and method of plastering
(a) Stages:
>First, the surface to be plastered is prepared. That is, it is cleaned with water and brushed.
>The plaster is prepared (preparation of mortar).
>The first coat is applied (First to ceilings and then o the walls).
>After a period not exceeding 5 days, the second coat is applied. And then after some time interval a finishing coat is applied.
>Aesthetic finishes such as rounding off corners etc., is done along with the finishing coat to avoid the appearance of joint marks.
(b) Methods
>The mortar is thrown (dashed) against the surface to be finished with the help of a rowel.
>The excess plaster is then removed with the help of wooden mason’s straight edge.
>With the help of wooden float, the plaster is prepared so that it fills the masonry joints.
>Now the surface is finished with the help of a trowel.
>By spraying water (fine fog spray) for a period of around 5 to 7 days, the coat of plaster is cured, the plastered surface keep damp during curing period.
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