How to Calculate Cement in Plastering? Plastering Ratio

Jan 17 2025

The well-finished building with fine walls and ceilings that have smooth surfaces involves not only skillful hands but also perfection that can only be attained with deep understanding of plastering ratios.

In other words, it is all about the proper proportion of cement, sand, and water.

Plastering plays an important part in any construction undertaking in adding not just beauty to the structure but strength to the surface also.

Read on to find out the mix ratio of plastering.

What is Plastering?

Plastering is a process in which a smooth or textured layer of material is applied over walls and ceilings.

It helps cover up imperfections, adds durability, and makes the walls look polished.

Think of it as putting a protective and decorative skin on your walls.

Plastering Work Ratio Calculation

Now, for better understanding, we are going to do this calculation for the 100 Sq. m area.

To calculate the cement and sand for 100 m2 plastering area in 1:6 ratio and 12 mm thickness.

Cement Mortar Required: Plastering thickness 12 mm = 12/1000 = 0.012m

Volume of cement mortar required = (Plastering Area x thickness) = 100 m2 x 0.012m = 1.2 m3

(This is wet volume, which means this much volume of cement mortar is needed after mixing water; for dry volume, we must add 30-35% as bulkage of sand; we are using 35%, and wastage as 20%)

Consider 35% Sand Bulkage = 1.2 m3 x (1+0.2+0.35) (Many of us would use 1.54 as constant)

= 1.86 m3

Cement: Sand (Ratio) = 1: 6 (Total = 1+6 = 7 Parts)

Cement required (1 Part) = 1.86 x 1/7

= 0.265 m3 /0.0347

= 7.66 bags (Approx – 8 Bags)

Sand required (5 Part) = 1.86 x 6/7

= 1.59 m3

We normally use Sq.m while calculating plastering cement mortar. If you want to calculate it in Sq.ft

Just convert that sq.ft into Sqm using Google Instant Area Conversion Tool and then use this formula.

Learn More: How to Calculate Cement in Brickwork?

Why is Cement Important in Plaster?

Cement is the glue of plaster, basically holding things together. Without cement, the mixture would be crumbly and would not possess strength.

Cement adds water resistance and wear resistance, letting your walls last longer and look good.

Types of Plastering

There are various types of plastering suited for different needs. Following are some common types:

1. Cement Plaster:

Most used in both exterior and interior walls due to its strength and durability.

2. Lime Plaster:

Lime plaster is very breathable and flexible. It is suitable for old buildings or places with variable temperatures.

3. Gypsum Plaster:

Great for a smooth, modern finish. It dries quickly but isn't suitable for damp areas.

Materials Needed for Plastering

Plastering involves using materials such as cement, sand, water, and sometimes lime or fiber reinforcements to make a smooth, durable surface.

Here is a simplified overview of the main materials:

1. Cement:

Cement acts as the glue in the plaster mix, holding everything together. It adds strength and durability.

Common types include Ordinary Portland Cement (OPC), Portland Pozzolana Cement (PPC), white cement, and Portland Slag Cement (PSC).

Learn More: Difference between OPC and PPC Cement

2. Sand:

Sand provides bulk to the mix, gives more workability, and avoids cracking. Its quality is of primary importance for a good finish.

Silica or quartz sand is often used for white or colored plaster applications.

3. Water:

Water is the element necessary for mixing and hardening the plaster.

Clean, drinking water should be used to prevent any effect on the quality of the plaster.

Seawater or brackish water is not suitable for this purpose, as it can weaken the plaster.

4. Lime:

Lime provides flexibility in the mix, making it more workable.

It helps reduce cracks and develops good bonding between the plaster and wall.

5. Fiber Reinforcements:

In some cases, natural fibers like jute, coconut, or hemp are added to the mix.

These fibers strengthen the plaster and minimize cracking.

They need to be clean, dry, and oil-free for the best results.

By combining these materials in the right proportions, you can achieve a high-quality plaster finish that’s both strong and long-lasting.

Conclusion

Plastering may seem technical, but it becomes manageable when broken down into steps.

Knowing how to calculate cement in plaster ensures your project runs smoothly and efficiently.

By measuring correctly, choosing the right mix ratio, and accounting for wastage, you can achieve a flawless plaster finish that stands the test of time.