Cement plaster/render; how its done

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:

Cement plaster ( 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

Cement plaster ( double coat)

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.

What to Plaster a Wall? See what you will need

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 Plastering
  • 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.
Gypsum plaster bag
  • 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.
Ready mix cement plaster

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

Types of Retaining Walls

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

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

Cantilever retaining wall

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 wall

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.

How to Calculate the amount of Cement , Sand and Coarse Aggregates required for construction of Reinforced Concrete Slab

Concrete slab

In this article we will determine how much of cement , sand and coarse aggregates will be required to construct a slab of length;10m, width; 5m and thickness 0.15m(150mm)

 Reinforced concrete is in the ratio 1:2:4.

Meaning one part of cement to two parts of fine aggregates to four parts of coarse aggregates.

Volume of the slab is length x breadth x thickness.

I.e 10 x 5 x 0.15= 7.5m³.

Dividing this volume in ratio 1: 2: 4

Volume of cement is;

(1/7)x 7.5=1.07m³

The density of cement is 1500kg/m³

 density= mass/ volume

Therefore mass of cement ;

1500x 1.07= 1605kg

A bag of cement weights 50kg so dividing 1650/50= 33 bags.

Mass of sand;

Volume of sand is( 2/7 )x 7.5= 2.14m³

Density of sand is 1700kg/m³

Therefore mass of sand = density x  volume;

1700 x 2.14= 3638kg

Mass of coarse aggregates;

Volume of coarse aggregates is (4/7)× 7.5= 4.29m³

Density of coarse aggregates is 1650kg/m³

Therefore mass of coarse aggregates,

1650 x 4.29= 7078.5 kg

Stair Design with Excel using RCC 71

RCC 71

The RCC 71 is an excel software developed by the Reinforced concrete council for the design of staircase. It designs to BS 8110: 1997. It can be used to design stairs, flight and landing.Upon starting the program you might see a macros warning. Enable macros if possible.

All blue text data are editable. Data which you will be required to enter include, dimensions of the staircase, concrete parameters and loading.

You do not need to do any previous major calculation before using RCC 71.

In the Flight tab of RCC 71, there are 4 input sections. They are the;

Project Name Title 



and Loading sections.

In the Project title section you can input the name of the project and so on

In the materials  section you can enter parameters such as strength of concrete, strength of steel, diameter of reinforcement and so on

The dimension section is where you enter the staircase dimensions such as length of thread, riser, thickness of waist..etc. 

In the loading section, you input the imposed loading and any other additional dead loads.

The design is longitudinal so the main bars are along the length of the stairs.

The software is a free to use version. A public release version.

To download RCC 71 and other structural design excel programs 


About Bamboo Scaffolding

Bamboo scaffolding

What is bamboo scaffolding? 

Bamboo scaffolding is simply scaffolding using bamboo stems. It is a cheaper alternative to the conventional scaffolding that uses hollow steel columns and struts.

How is bamboo scaffolding constructed?

The bamboo stems are connected together using big five inches long nails and binding wire. The column bamboo stems must be braced. The column stems are usually spaced 1.5m apart..For added strength and rigidity, bamboo struts that support the platform on which workmen will stand are bored into the wall.

Another view of bamboo scaffolding

 How reusable is bamboo scaffolding?

Bamboo is still reusable a few times. You can also dismantle bamboo scaffolding and erect in another section of the building if you don’t have enough scaffolding to go round the whole building.

How much bamboo stems is need for a typical building?

The number of bamboo stems a building will need depends on the perimeter of the building and its height. A typical story building that is about 6m high will need about 120 bamboo stems to construct scaffolding for it at once.

How to construct bamboo scaffolding based on its properties.

Bamboo stems are very strong in compression and rigidity. Bamboo stems good for scaffolding should be at least 6cm and above.Use bamboo stems with higher diameter for struts, beams and bracings.