Preparation of Cement Mortar

Preparation of Cement Mortar

For preparing mortar, water is added to intimate mixtures of  binding  material and sand.  The water to  be used for this purpose should be  free  from  clay,  earth  and other impurities.Water which is fit for drinking should only be used for preparing mortar.

Cement mortar may be prepared by manual mixing or by mechanical mixing. Mechanical mixing is preferred when mortar is required in large quantities to be used in continuous order.

  1. Mixing in the mechanical mixer:  In  this  case, cement and sand in desired proportion are fed in the mixer and mixed dry.Water is then  added gradually and the wet mixing a continued for at  least  one  minute to obtain the  mortar  of desired consistency. It is necessary to ensure that only the quantity of mortar which can be used within half an hour of its mixing should be prepared at a time. This is essential as after 30 minutes the mortar begins to set.
  2. Manual mixing: In this case, specified quantity of sand is spread and  leveled on clean dry masonry platform.Required quantity of cement bags are emptied over the sand layer. The ingredients are then mixed thoroughly by turning them  over the sand layer.The ingredients are  then  mixed thoroughly by turning them over and over. Backward and forward several times with the help of spade. Dry mixing is continued till the  mix have attains a uniform colour.  A batch  of dry mix is then put in  the shallow masonry tank and just sufficient quantity of water is  added  to  bring  the mortar  to the consistency of  a  paste.  The quantity of  dry mix taken in each batch should be such the mortar formed each time is consumed within half an hour.

Precautions in using mortar

  1. Consumption of mortar –   the  consumption  of  mortar should be as early as possible

Line mortar       –   with  in  36  hours  after  its preparation

Cement mortar     –   within 30 minutes

Gaged mortar      –   within 2 hours.

  1. Frost action – Setting action of mortar is affected by the presence of frost and not advisable in frosty weather.
  2. Soaking of building units: Building units should not be soaked before application of mortar. If this precaution is not taken, water of mortar will be absorbed by the building units and mortar will become weak.
  3. Sprinkling of water:  The construction work carried out by mortar should be kept dam or wet by sprinkling water for about 7 to 10 days to avoid rapid drying of mortar.
  4. Workability: Mortar  should not contain excess water and it should be stiff as can be conveniently used. Joints should be well formed and excess mortar from joints should be neatly taken off by a trowel. Surface formed by mortar for building units to rest should be even.