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PLASTER
[Other-than cement plaster]
There are two basic types of plasters - Lime Plaster & Gypsum Plaster. The
former is not really in use now and should be avoided.
There are five types of Gypsum Plaster. 
Plaster of Paris 
Retarded Hemi-hydrate 
Anhydrous
Keene’s
Lightweight
Plaster of Paris sets quickly and is mainly used in small batches for repair work
and casting. Retarded Hemi-hydrate is Plaster of Paris to which organic
substances have been added to retard the setting. Anhydrous and Keene’s
plasters are slow setting, requiring the addition of accelerators if quicker setting
is needed. 
Lightweight plasters are premixed, requiring only the addition of water. They 
consist of lightweight aggregate, usually perlite or vermiculite and Gypsum 
Plaster. Within the range also comes acoustic plasters, barrier plasters for X 
– Ray rooms,
plasters for squash courts and other similar specialist uses.
Because of the continual movement of moisture towards the surface as new
plaster dries, a permeable coating is essential to allow passage of moisture
vapor into the atmosphere. An oil based impervious coating must never be used
on plaster that has not completely dried out thoroughly. 
Emulsion paints are recommended for newly plastered surfaces but even these
coating are subject to premature loss of adhesion if the moisture level is high.
Therefore, as long a drying period as possible before painting is beneficial. 
Surface Preparation:
Remove any Plaster ‘nibs’ or scum and fill in or stop cracks and holes. Remove
& treat if there is any efflorescence (see Efflorescence). Abrade any areas of
over-toweled ‘glossy’ plaster with worn abrasive paper. Dust off with clean cloth. 
Painting:
1 – 2 coats PLASTRON or BISON PRIMER 
2 Coats of SPD/ APE/ Luxury Silk
N. B. For glossy finish oil-based paints like air-drying enamel may be applied
over 1-2 coats of above primer but it should be well ensured that the plastered
surface is completely dry.