Cement Plaster

Cement plaster is a mortar of cement, sand and water applied to masonry or concrete surfaces to give a smooth, true, durable base for paint and to protect the substrate from weather. Internal plaster is commonly 12 mm in a 1:4 to 1:6 cement:sand ratio; external plaster is usually 15–20 mm and richer (1:3 to 1:4), often in two coats, with a 1:3 'neeru'/punning or sponge finish. Mix proportions, surface preparation, thickness and curing follow IS 1661 (cement and cement-lime plaster) and the mode-of-measurement rules of the relevant IS 1200 part.

The dominant defects — cracking, debonding/hollowness, and efflorescence — almost always trace to workmanship, not material: rich mixes shrink and craze, dry substrates suck water and cause poor bond, and inadequate curing (minimum 7 days moist curing) weakens the coat. Surfaces must be hacked/roughened and pre-wetted, plaster applied in controlled thickness with proper gauging, and external work protected from direct sun and wind during curing. Gypsum plaster (IS 2547) is an increasingly common faster internal alternative that needs no water curing.