Cement-sand plastering and its types

Plastering is the process of covering rough walls and ceilings with a coat of cement-sand mortar to give a smooth, even, durable and good-looking surface that also protects against weather.

Types of cement-sand plaster

• Single coat plaster: 12-15 mm in one coat, for ordinary work.
• Two-coat plaster: 12 mm base coat and 6-8 mm finishing coat; most common.
• Three-coat plaster: 9-12 mm scratch coat, 6-8 mm floating coat, 2-3 mm finishing coat; best quality.
• Sand-faced, rough cast, pebble dash and stucco are decorative finishes.

Proportion

Cement-sand 1:4 for external walls (1:6 for internal walls) and 1:3 for finishing coats and ceilings.

Procedure

1. Preparation: rake out the joints 10-12 mm deep; clean the surface of dust and oil; wet the wall.
2. Fixing guides: vertical lines are marked with plumb bob; patches of plaster or screed strips (gauges) are placed at 2 m c/c in level with the final plaster face.
3. Mortar preparation: cement and sand are mixed dry, and then water is added to get a workable mix.
4. Applying the first coat (scratch coat): mortar is thrown with a trowel and pressed firmly; surface is levelled with a flat wooden rule and scratched to form a key.
5. Second coat: after the first has set (1 day), apply 6-8 mm of floating coat, levelled.
6. Finishing coat: rubbed with a wooden float or trowel for a smooth or textured finish.
7. Curing: keep wet for at least 7 days.

   wall|scratch coat|floating|finish
       | 12 mm      | 8 mm   | 3 mm