Description about mortar, classification, properties, tests & uses of mortar

 

·         Building mortar is define as a mixture of cement, sand and water.

·         Mortar is similar to concrete but it does not contain coarse aggregate.

·         Mortar are used for filing joints as a binder in stone and brick masonry

 

Bulking of sand

·         In the case of aggregates there is another effect of the presence of moisture viz. bulking which is an increase in the volume of a given sand particle apart. for a moisture content of about 5-8 % depending upon the  increase of volume may be as much as 20-40% depending upon the grading of sand .

·         Finer the materials more will be the increase in volume for a given moisture content.

Classification of mortars

·         Mortars are classified on the basis of the following.

(i)            Bulk density

(ii)          Kind of binding materials

(iii)         Naturals of application

(iv)         Special mortars

Properties of a good mortar

The important properties of good mortar mix are mobility, place and water retention.

·         Mobility

·         It used to indicate the consistency of mortar mix which may range from stiff to fluid.

·         The mobility of mortar mix depends the composition of mortar and the mortar mixes to be used for masonry work are made sufficiently mobile

 

Place ability

·         The place ability of mortar mix should be such that a strong bond is developed with the surface of the bed.

Properties of a good mortar

·         It should be capable of developing good adhesion with the building units such as brick, stone etc.

·         It should be capable of developing the designed stresses.

·         It should be cheap.

·         It should be durable workable.

·         It should set sulky so that speed in construction may be achieved.

Uses of mortar   

·         To carry out pointing and plaster work on exposed surfaces of masonry.

·         To form joints of pipes.

·         To hide the open joints of brickwork and stonework.

·         To improve the general appearance of structure.

·         Functions of sand in mortar

1 bulk      2 setting 3 shrinkage   4 strength.

 

Test for mortars:

1.    Adhesiveness to building Unit: Mortar is placed to join them so as to from a horizontal joint. If size of bricks is 19cm x 9cm x 9cm, a horizontal joint of 9cm x 9cm 81 cm² will be formed^. Ultimate adhesive strength of mortar per cm² area is obtained by dividing maximum load 81cm² area.

2.    Crushing Strength: Brick masonry or stone masonry laid in mortar to be tested are crushed in compression machine. The load at which the masonry crushes gives the crushing strength.

3.    Tensile Strength: The briquettes are tested in tension testing machine cross sectional area of central portion is 38mm x 38mm or 1444 mm².

 

GUNITING:

·         The guniting is the most effective processes of repairing concrete work which has been damaged due to inferior work or other reasons. It is also used for providing an impervious layer.

·         Guniting is mixture of cement and sand, the usual proportion being 1:3. A cement gun is used to deposit the mixture on the concrete surface under a pressure of about 2 to 3 kg/cm².

·         The surface to be treated is cleaned and washed. The nozzle of gun is generally kept at a distance of about 75cm to 85cm from the surface to be treated and velocity of nozzle varies from 120 to 160 m/sec.