What Is Thumb Rule?
Thumb rule is an approximate method for doing something. This particular method is based on the practicality of an activity rather than its theory, that’s why it is known as an approximate method. This method is not accurate. It provides the results or the values approximately, but nearer to its perfect result.
Thumb rule is a method on which one cannot rely in every situation due to its lesser accuracy relatively, but still, it is used widely on construction sites as it seems easier to engineers.
One of the advantages of using thumb rules is that one can get on a spot solution for a particular activity or a problem. It gives some really quick answers to the questions arising on site, making the work a lot easier for the engineers and site in charge.
Let us learn about some of the thumb rules which are frequently and popularly used by engineers on site.
Thumb Rule 1:
Quantity Of Steel Used In Beam, Column, Slab & Footing:
Quantity of steel for,
Residential structure = 4.5 kg to 4.75 kg per square feet.
Commercial structure = 5 kg to 5.50 kg per square feet.
Quantity Of Steel In Different Structural Members
Slab = 1 % of total volume of concrete in slab.
Beam = 2 % of total volume of concrete in beam.
Footings = 0.8 % of total volume of concrete in footings.
Column = 2.5 % of total volume of concrete in column.
Let’s take an example of a slab and calculate the quantity of steel in the slab of size = 8m x 6m x 0.15m
The quantity of steel in a slab is 1 % of total volume of concrete. So we need to calculate the quantity of concrete in this slab.
Total quantity of concrete = 8 x 6 x 0.15 = 7.2 m3.
Now, calculating the quantity of steel = total volume of concrete x density of steel x 0.01
= 7.2m3 x 7850 kg/m3 x 0.01
= 565.2 kg.
The total quantity of steel required in the given slab is 565.2 kg.
Similarly for other structural components, the quantity of steel can be worked out.
Note – it is found that for 1000 kg of steel (1000 kg = 1 ton), 7 kg to 13 kg of binding wire is used. This is an approximation hence the variation is there in the quantity of it.
Thumb Rule 2:
Quantity Of Concrete With Respect To Area
For 1 square feet of area, an approximate quantity of 0.038 m3 of concrete is taken.
For example, if the plan area is 1500 square feet, the quantity of concrete is calculated as follows:
Area = 1500 square feet
Quantity of concrete per square feet = 0.038 m3
Total quantity of concrete required = 1500 x 0.038
= 57 m3.
Thumb Rule 3:
Quantity Of Shuttering (Formwork) And Its Components
It is taken as 6 times the total quantity of concrete or 2.4 times the area of the plinth. Suppose the quantity of concrete is 10 m3, then the area of shuttering is,
6 x 10 = 60 m2.
Quantity Of Shuttering Ply:
Quantity of shuttering ply is calculated by multiplying the area of shuttering by 0.22.
For example, if the area of shuttering is 5 m2, then the quantity of shuttering ply required is,
0.22 x 5 = 1.1 m2
Quantity Of Battens:
When the number of ply sheets is multiplied with 19.82, we get the total quantity of battens. For example,
If there are 50 ply sheets, then the quantity of batten is calculated as follows:
50 x 19.82 = 991 battens.
Quantity Of Shuttering Oil:
The quantity of shuttering oil required can be considered in two ways. They are,
0.065 times of the total area of shuttering Or
1 litre of oil is consumed for 15 m2 of shuttering area. For example, if the area of shuttering is 20 m2 then, 20/15 = 1.33 litres of shuttering oil is required.
Quantity Of Nails And Binding Wire:
An approximate quantity of 75 grams of nails is required for every 1 m2 of shuttering area and similarly, 75 grams of binding wire is approximately required for every 1 m2 of shuttering area.
Thumb Rule 4
Quantity Of Cement, Sand, Aggregates In Different Concrete Grades
|Sr. No.||Grade Of Concrete||Quantity Of Cement (Bags)||Quantity Of Coarse Aggregates (m3)||Quantity Of Fine Aggregates (Sand) (m3)|
|1||M 5 (1:5:10)||2.82||0.98||0.49|
|2||M 7.5 (1:4:8)||3.48||0.97||0.48|
|3||M 10 (1:3:6)||4.50||0.90||0.45|
|4||M 15 (1:2:4)||6.60||0.88||0.44|
|5||M 20 (1:1.5:3)||8.40||0.84||0.42|
Note – 1 bag of cement weighs 50 kg.
Thumb Rule 5
Quantity Of Cement In Brickwork
|Sr. No.||Brickwork (1 m3)||Quantity Of Cement in Bags per m3||Quantity Of Cement in kg per m3|
|1||230 mm brickwork||0.876 bags per m3||43.80 kg per m3|
|2||115 mm brickwork||0.218 bags per m3||10.90 kg per m3|
Thumb Rule 6
Quantity Of Cement In Cement Masonry
|Sr. No.||Cement Masonry Type And Mix||Quantity Of Cement In Bags per m2||Quantity Of Cement In Kg per m2|
|1||200 mm in cement masonry work of ratio 1:6||0.124 bags per m2||6.2 kg per m2|
|2||150 mm in cement masonry work of ratio 1:6||0.093 bags per m2||4.65 kg per m2|
|3||200 mm in cement masonry work of ratio 1:4||0.206 bags per m2||10.3 kg per m2|
|4||150 mm in cement masonry work of ratio 1:4||0.144 bags per m2||7.2 kg per m2|
|5||100 mm in cement masonry work of ratio 1:4||0.103 bags per m2||5.15 kg per m2|
Thumb Rule 7
Quantity Of Cement For Different Types Of Plaster
|Sr. No.||Type Of Plaster||Quantity Of Cement In Bags Per m2||Quantity Of Cement In Kg Per m2|
|1||Rough plaster||0.09 bags per m2||4.5 kg per m2|
|2||Internal wall plaster||0.09 bags per m2||4.5 kg per m2|
|3||External wall plaster||0.175 bags per m2||8.75 kg per m2|
|4||Duct plaster||0.09 bags per m2||4.5 kg per m2|
|5||Stucco plaster||0.175 bags per m2||8.75 kg per m2|
|6||Lathen plaster||0.55 bags per m2||27.5 kg per m2|
Thumb Rule 8
Labour Productivity For Different Construction Activities
Labour productivity is measured for work done for 8 hours per day, by a single person or a pair of labours.
|Sr. No.||Construction Activity||Quantity Of Work||Manpower Deployed|
|1||Brick work||1.5 square metre||1 mason, 1 male helper, 1 female helper|
|2||Block work (200 mm blocks)||12 square metre||1 mason, 1 male helper, 1 female helper|
|3||Wall plaster||1.12 square metre||1 mason, 1 male helper, 1 female helper|
|4||External wall plaster||7.85 square metre||1 mason, 1 male helper, 1 female helper|
|5||Ceiling plaster||7 square metre||1 mason, 1 male helper, 1 female helper|
|6||Shuttering work||5 square metre||1 carpenter and 1 unskilled labour|
|7||Tile work||12 square metre||1 mason and 1 helper|
|8||Steel binding||250 kg||1 fitter and 1 helper|