### What is Sand Cement Plaster?

Sand cement plaster is a mixture of sand, cement, and water that is applied to the surface of a structure to form a hard and smooth layer. Sand cement plaster is also known as cement plaster or cement sand plaster. The ratio of sand cement plaster determines the strength, workability, and durability of the plaster. The ratio of sand cement plaster is usually expressed as 1:n, where 1 is the part of cement and n is the part of sand. For example, a ratio of 1:6 means that for every one part of cement, there are six parts of sand.

### Factors Affecting the Ratio of Sand Cement Plaster

The ratio of sand cement plaster depends on various factors, such as:

– The type and quality of the surface to be plastered. Different surfaces have different absorption rates, porosity, and texture, which affect the amount of water and cement required for plastering. For example, brickwork and masonry surfaces require more water and cement than concrete surfaces, as they are more porous and rough.

– The thickness and area of the plaster. The thickness and area of the plaster affect the quantity and consumption of the materials. Generally, the thickness of the plaster should be between 10 mm to 15 mm, depending on the surface and the purpose of the plaster. The area of the plaster can be calculated by multiplying the length and width of the surface.

– The quality and grade of the materials. The quality and grade of the materials affect the strength and durability of the plaster. The sand used for plastering should be clean, coarse, and well-graded, without any impurities or organic matter. The cement used for plastering should be fresh, dry, and of the appropriate grade, such as 43 or 53 OPC or PPC. The water used for plastering should be clean and potable, without any salt or acid content.

– The environmental conditions and the curing time. The environmental conditions and the curing time affect the setting and hardening of the plaster. The plaster should be applied in a moderate temperature and humidity, avoiding direct sunlight, rain, or wind. The plaster should be cured properly for at least 7 days, by sprinkling water at regular intervals, to prevent cracking and shrinkage.

### How to Calculate the Ratio of Sand Cement Plaster for Different Surfaces

The ratio of sand cement plaster for different surfaces can be calculated by using the following steps:

– Step 1: Determine the area and thickness of the plaster. Measure the length and width of the surface to be plastered, and multiply them to get the area in square meters or square feet. Decide the thickness of the plaster in millimeters or inches, and divide it by 1000 or 12 to get the thickness in meters or feet. Multiply the area and the thickness to get the volume of the plaster in cubic meters or cubic feet.

– Step 2: Choose the ratio of sand cement plaster. Based on the type and quality of the surface, choose the appropriate ratio of sand cement plaster. For example, for brickwork and masonry surfaces, a ratio of 1:6 is commonly used, while for concrete surfaces, a ratio of 1:4 is preferred. You can also consult the standard specifications or the engineer’s recommendations for the ratio of sand cement plaster.

– Step 3: Calculate the quantity of cement and sand. To calculate the quantity of cement and sand, use the following formula:

Quantity of cement = (Volume of plaster x Ratio of cement) / (Sum of the ratio)

Quantity of sand = (Volume of plaster x Ratio of sand) / (Sum of the ratio)

For example, if the volume of plaster is 10 cubic meters, and the ratio of sand cement plaster is 1:6, then the quantity of cement and sand are:

Quantity of cement = (10 x 1) / (1 + 6) = 1.43 cubic meters

Quantity of sand = (10 x 6) / (1 + 6) = 8.57 cubic meters

– Step 4: Convert the quantity of cement and sand into weight and bags. To convert the quantity of cement and sand into weight and bags, use the following conversions:

1 cubic meter of cement = 1440 kg

1 cubic foot of cement = 94 lb

1 bag of cement = 50 kg or 110 lb

1 cubic meter of sand = 35.31 cft

1 cubic foot of sand = 100 lb

For example, if the quantity of cement is 1.43 cubic meters, and the quantity of sand is 8.57 cubic meters, then the weight and bags of cement and sand are:

Weight of cement = 1.43 x 1440 = 2059.2 kg

Bags of cement = 2059.2 / 50 = 41.2 bags

Weight of sand = 8.57 x 35.31 x 100 = 30248.7 lb

Cubic feet of sand = 8.57 x 35.31 = 302.5 cft

– Step 5: Add the required additives and water. To improve the quality and performance of the plaster, you can add some additives, such as plasticizers, waterproofing agents, or fibers, according to the manufacturer’s instructions. You can also adjust the water content of the plaster, depending on the workability and consistency required. Generally, the water-cement ratio for plastering should be between 0.4 to 0.6. To calculate the quantity of water, use the following formula:

Quantity of water = Weight of cement x Water-cement ratio

For example, if the weight of cement is 2059.2 kg, and the water-cement ratio is 0.5, then the quantity of water is:

Quantity of water = 2059.2 x 0.5 = 1029.6 liters

### Examples of Calculating the Ratio of Sand Cement Plaster for Different Surfaces

To illustrate the calculation of the ratio of sand cement plaster for different surfaces, let us take some examples:

– Example 1: Calculate the ratio of sand cement plaster for a brick wall of 100 sqft area and 12 mm thickness, using a ratio of 1:6.

Solution:

– Area of the wall = 100 sqft

– Thickness of the plaster = 12 mm = 0.012 m

– Volume of the plaster = Area x Thickness = 100 x 0.0929 x 0.012 = 0.1115 cubic meters

– Ratio of sand cement plaster = 1:6

– Quantity of cement = (0.1115 x 1) / (1 + 6) = 0.0159 cubic meters

– Quantity of sand = (0.1115 x 6) / (1 + 6) = 0.0954 cubic meters

– Weight of cement = 0.0159 x 1440 = 22.9 kg

– Bags of cement = 22.9 / 50 = 0.46 bags

– Weight of sand = 0.0954 x 35.31 x 100 = 336.8 lb

– Cubic feet of sand = 0.0954 x 35.31 = 3.37 cft

– Water-cement ratio = 0.5

– Quantity of water = 22.9 x 0.5 = 11.45 liters

– Example 2: Calculate the ratio of sand cement plaster for a concrete ceiling of 100 sqm area and 10 mm thickness, using a ratio of 1:4.

Solution:

– Area of the ceiling = 100 sqm

– Thickness of the plaster = 10 mm = 0.01 m

– Volume of the plaster = Area x Thickness = 100 x 0.01 = 1 cubic meter

– Ratio of sand cement plaster = 1:4

– Quantity of cement = (1 x 1) / (1 + 4) = 0.2 cubic meters

– Quantity of sand = (1 x 4) / (1 + 4) = 0.8 cubic meters

– Weight of cement = 0.2 x 1440 = 288 kg

– Bags of cement = 288 / 50 = 5.76 bags

– Weight of sand = 0.8 x 35.31 x 100 = 2824.8 lb

– Cubic feet of sand = 0.8 x 35.31 = 28.25 cft

– Water-cement ratio = 0.5

– Quantity of water = 288 x 0.5 = 144 liters