Already we discussed the concrete material calculation

So, in this post, we are going to discuss how to calculate cement and sand for plastering work with an example calculation.

Before getting into the calculation, Let’s learn some basics

Common plastering mortar thickness and mix ratio listed below.

 LOCATION THICKNESS RATIO External Wall 20mm 1:6 Internal Wall 15mm 1:4 Ceiling 12mm 1:3

## Quick Check ## Plastering Calculation

Assume we need to calculate plastering material quantity for 10 X 10 m ceiling.

• Required Plastering Area = 10 x 10 = 100 m2 or Square Metre
• Plastering thickness = 12 mm
• Cement Mortar Ratio = 1:3 (1 Part Cement : 3 Part Sand)

Required volume of Cement Mortar = plastering area x plastering thickness = 100 x 0.012 = 1.2 m3

### Adding Bulking of Sand & Wastage

So to get 1.2 m3 of wet cement mortar, we have to multiply the dry volume by 1.55.

What is 1.55 constant in the calculation?

1. Bulking of Sand If the moisture is present in the sand, then it makes the sand look bulkier, which could result in inadequate sand proportion in the concrete ratio.

For Example, If we need to add 1m3 sand in the concrete mix ratio, we take 1.3 m3 (30% more). The reason for that is the moisture content present in the sand makes it a little bulkier. The 5% to 8% of surface moisture will increase the bulking of sand up to 20% to 30%. When we add more water (more than 8%) to the sand, the thin film will disappear, and volume decreases.

2. Wastage – Adding 20% wastage for joints and impressions filling

So if we need 1 m3 of cement mortar in wet condition we have to take consideration of the bulking of sand & wastage as (34%+20%) = 54%

Thus every time you need to calculate the volume of cement mortar you need to add the above percentage with dry volume

Wet Volume of concrete = Dry Volume of concrete + 54% of dry volume of concrete or

Wet Volume of concrete = Dry Volume of concrete x 1.54

So whatever volume we get from the above formula, we need to multiply the value with 1.54% So total part of mortar = 1+3 = 4

Therefore,

• Required Volume of Cement = 1/4 x 1.55 (Bulkage & Wastage) x Mortar Volume

= 1/4 x 1.55 x 1.5= 0.581 cum

To convert into cement bags  – (0.581 x 1440)/50 = 16.7 Bags

Unit weigh of Cement – 1440 Kg/m3    1 bag cement – 50 Kg

• Required Sand Volume = 3/4 x 1.55 (Bulkage & Wastage) x Mortar Volume

= 3/4 x 1.55 x 1.5 = 1.74 m3

So the required quantity of material for 100 sqm plastering with mortar thickness 15mm & mix ratio 1:3 is

• Cement = 16.7 Bags
• Sand = 1.74 m3 Bala is a Planning & QS Engineer working at Megha Engineering & Infrastructure Limited who has more than 9+ Years of experience in Building & Infrastructure. He is the author, editor of Civil Planets.

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