Cement and sand are mixed in the dry state in the adopted ratio. For plastering of walls, a cement sand ratio 1: 6 is adequate.

Water is added to achieve a workable plasticity.

Cement plaster can be applied in 2 coats or as a single coat. Plaster thickness for walls ranges from between 12mm to 20mm. Plaster thickness of between 12 and 15mm can be applied as a single coat while thickness above 15mm are applied in 2 coats.

Cement Plastering in a single coat:

The plaster is first applied roughly at the required thickness on the wall. Wait for about 20 minutes, (After the plaster starts to set), and gradually smooth it out with a straight long rod or plank. The plastering is then finished off with a hand trowel and finally foaming. The finished work should be straight and smooth.

Cement plastering in 2 coats

This method is necessary when the plaster thickness is above 15mm. The first coat is applied roughly on the surface of the wall. The surface of the plaster is then made zigzag to receive the second coat. The second coat can be applied when the first coat sets ( about 30mins upwards). However it should be applied by the second day at the latest.

Plastering a wall means you want to give the wall a smooth and level finish with the use of a cementitious compound. Plaster is a protective or decorative coating for walls and ceiling.If a wall is constructed of sandcrete blocks then chances are high that it will be plastered to give a very smooth aesthetic finish.

Difference between plastering and rendering

“plaster” usually means a material used for the interiors of buildings, while “render” commonly refers to applications on external walls.

Types of plaster

• Gypsum plaster: Also called plaster of Paris, it is calcium sulphate hemihydrate a white cementing material composed of gypsum, retarded and hardeners. It is applied to the wall in a plastic state. It thereafter hardens by the chemical combination of the gypsum and water. Gypsum plaster are usually supplied in bags.

• Cement plaster: This is a mixture of portland cement and sand. It is applied in the plastic state after mixing with water. It thereafter hardens after the chemical combination of the cement and water. Ready mix cement plaster is supplied in bags.

Cement plaster

This is the most commonly used plaster material because it is cheaper and more versatile than the gypsum plaster.

Ready mix cement plaster is available but expensive. It is more economical to mix on site, cement, sand and water and use it to plaster / design walls.

Materials needed for cement plaster

1. Cement: usually supplied in 50kg bags.
2. Plaster sand. A type of fine sand that bonds very well with cement in the presence of water.
3. Clean water of drinking quality.

Mixing of cement and sand for plaster works

Thorough mixing of cement and sand is first done in the dry state. After that water is added and mixed to a workable plastic state before application. For plastering works, the cement sand ratio is usually 1:4 or 1:6. Ratio 1:6 being the more commonly adopted ratio.

To calculate the amount of cement and sand need for wall plastering, read the article below by clicking on the link.

How to calculate the number of cement bags and quantity of sand required for plastering

Retaining walls are structures designed to retain earth and hydrostatic loadings. Retaining walls should be capable of holding retained material in place without undue movement of overturning, sliding or deflection.

Types of Retaining Wall.

There are three major types namely;

1. Gravity
2. Counterfort
3. Cantilever 

Gravity retaining wall

These types are usually constructed of mass concrete. Reinforcement is only included in the faces to limit thermal and shrinkage cracking. Gravity retaining wall relay on its self weight to hold retained material in place.

Cantilever retaining walls

These walls reinforced concrete retaining walls economically designed. They have a very large base and rely heavily on the backfilling of their base for strength.

Counterfort Retaining Walls

Counterfort retaining walls are cantilever retaining walls supported by a type of bracings called counterforts. counterforts become necessary when the design of cantilever retaining wall becomes uneconomical or when the overall height of the wall is too high.

To design retaining walls you will have to consult specialized textbooks and the relevant code of practice.