Tuesday, January 21, 2014

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How to plaster on surface

Plaster is a mixture of sand and cement with water. 1:4 or 1:6 ratio of cement-sand is mixed for making plastering mortar. 1:4 cement-sand mortar is used for plastering masonry surface and 1:6 cement-sand mortar is used for RCC surface plastering. The thickness of plaster on surface is ranging from 12mm to 25mm depending on the surface condition.

Purpose of plastering:
Plaster is used for covering the rough surface of RCC and masonry work to obtain a smooth, even, regular, clean and durable surface and with the object of improving the resistance of the surface to rain water penetration and atmospheric influences.

Construction process of plastering:

Surface preparation-

·        First of all, chip the RCC surface
·        Brush and scrap the cured surface to make it free from mortar, oil, greasy spots and efflorescence and loose materials.
·        Wash the surface with water and keep it moist before commencing plaster. But no excess water will be on surface and it will be saturated and dry.
Mixing materials-

·        Separate the foreign materials and larger particles from sand with the help of sieve.
·        Measure the required quantity of sand and keep them in a dry and plane place.
·        Spread the measured cement on sand
·        Mix the dry volume of cement & sand until the mixture is uniform. Then add water gradually till the mix is plastic.
Application of plaster-

·        Apply cement grout on RCC surface.
·        Make 75mm x 75mm patch of plaster @ 2 – 3 m c/c as reference level of plaster.
·        Apply the mortar on surface.
·        Check the level of the surface with thread and spirit level. Check should be made for each 5 square meter of finished surface area. If the surface is not level then redo the area by scratching when the mortar is still green.
·        Finish the surface with wooden trowel, broom and wetted foam. Wetted foam is used to prevent water percolation from cement mortar.
·        Cure the finished plastered surface after 24 hours with water continuously for at least 14 days.
Important notes to care -

·        Do not apply dry cement-sand mix on the prepared surface.
·        The mortar should be used within 1 hour after mixing adding water with cement-sand mix.
·        Add water proofing agent 0.25% by weight of cement for plastering of basement wall, reservoir and water retaining wall. For outside plastering of building add water proofing agent 0.50% by weight of cement.


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