Process of covering rough surface with a plastic material to obtain an even, smooth, regular and clear and durable surface is known as plastering.
Plaster may be-
(i) Lime plaster – Gradual shrinkage, soften, damaged by knock mixed with animal hair to give strength, discolour any decoration.
(ii) Cement plaster
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(iii) Stucco plaster
(iv) Gypsum plaster-Expand slightly
Defects in plaster work are
(i) Cracking – old surface not being properly prepared. Movement is the backing materials. Backing surface should be allowed to dry before applying plaster.
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Movement in the plaster
Excessive shrinkage of plaster
Workmanship and method of application, vibration
Dampness formation of salt crystal that gradually push the plaster outwards.
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Cracked plaster should be cut away & the area should be plastered.
(ii) Blowing/blistering of plaster
(iii) Falling out plaster.
(iv) Efflorescence.
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If soluble salts are present in bricks or the mortar, they may absorb moisture from atmosphere and go into solution which appears on the surface in the form of whitish substance as the moisture dries out and the salt crystallize the suffice gets disfigured and concentrated strains present an ugly presence. Efflorescence may occur on brick work or on the surface of plaster.
Efflorescence on the surface is less likely to cause any real damage to the bricks unless the quantity of soluble salts present is abnormal. If the formation of crystal (on drying) of the salt solution of the material and cause severe flaking of the plastered surface. Efflorescence on the surface can be removed to some extent by brushing and washing the surface repeatedly.
In case of back work salts can be removed by Appling a solution of zinc sulphate and water and then brushing of the surface when it is dry.
A solution consisting of one part of hydrochloric or sulphuric acid diluted with 5 parts of water is applied on the surface with scrimping brush. The surface is then thoroughly washed and rendered clean and dry.