Formation of thumb rules for cement, sand and aggregates
The purpose of thumb rules is to prepare the rough cost of the building or plain quantities estimates. You can’t get a perfect quantity with the thumb rule rather a rough quantity that is almost identical or less to the accurate quantity.
Definition of thumb rule: Thumb rule is defined as creating a constant number with previous experience as well as work experience in the jobsite each day. As for instance, required covered area is multiplied with thumb rule to obtain rough quantities of the material.
You can get more clear ideas on thumb rule on the basis of the following example :-
Assume that 3 different houses are built up with a covered Area of 1050 square feet each. In every house various quantities of Cement bags, Sand and Aggregates are utilized for the construction work. Therefore, a thumb rule is formulated for cement, sand and aggregates quantity estimations as follow :-
IN 1ST HOUSE CONSTRUCTION:
Cement = 600 Bags (as for illustration).
Sand = 2,000 cubic feet.
Aggregates = 1700 cubic feet.
IN 2ND HOUSE CONSTRUCTION:
Cement = 590 Bags (as for illustration).
Sand = 1900 cubic feet.
Aggregates = 1600 cubic feet.
IN 3RD HOUSE CONSTRUCTION:
Cement = 570 Bags (just for example).
Sand = 1800 cubic feet.
Aggregates = 1500 cubic feet.
How thumb rule is formed here :-
To form thumb rule for every construction material, the average usage of every particular material should be selected.
Average Consumption = (600 + 590 +570)/3
= 586.66 bags.
Now it is required to determine the quantity of cement that is used in 1 square feet area.
Covered area = Material consumption.
1050 sft = 586.66 bags..
1sft = (586.66/1050) bags.
1sft = 0.55 bags
So 0.55 is fundamentally considered as our cement thumb rule. Now, if it is required to work out the quantities of cements for 5,000 square feet area (if the conditions are identical), 0.55 should be multiplied with the covered area to obtain the cement quantity.
To get more information on how to create thumb rule for sand and aggregates, go through the following link civilclick.com