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.
- 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.
- 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
- 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.
- Frost action – Setting action of mortar is affected by the presence of frost and not advisable in frosty weather.
- 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.
- 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.
- 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.