Below are the techniques used by professionals for determining how much of each ingredient will be required to make a mixture that is correctly sized and proportioned for any given piece of work. The only part that might get tricky is figuring out the volume of more complicated shapes, but I’ll leave that part for you to work out. And, while this is for “estimating” purposes, I’ve found it to be surprisingly accurate.
This technique involves first determining the actual volume of a piece, multiplying that by an industry standard factor of 1.65 (which includes 10% extra to compensate for any losses), breaking the mix ratio down into “Parts”, calculating a volume for each part and then multiplying the volume per part times the number of parts. (Unless you are much better at math than I, a pocket calculator will probably come in handy.)
Here we go…
A single 2” x 16” x 16” Stepping Stone made with a standard “1-2-3” concrete mix (1 part Cement plus 2 Parts Sand plus 3 Parts Gravel).
Calculating Volume Per Component:
1. First, calculate the “Actual Volume” of the piece…
2”x16”x16” = 512 cu. in.
2. Then convert that Actual Volume into an “Estimated Total Volume of Dry Material” by multiplying times the factor of 1.65…
512 x 1.65 = 844.8 cu. in.
3. Now add up the total number of “Parts” that make up the mix…
1 Part cement + 2 Parts sand + 3 Parts gravel = 6 total “Parts”
4. Then, to determine the Ingredient Volume by Part, divide the Total Volume of Dry Material by the total number of Parts…
844.8 cu. in. divided by 6 Parts = 140.8 cu. inches per each Part.
5. Now simply multiply the Ingredient Volume by Part, times each components specified number of Parts, and you’ll have the volume for each component…
a. Cement = 1 Part x 140.8 cu. in. = 140.8 cu. in.
b. Sand = 2 Parts x 140.8 cu. in. = 281.6 cu. in.
c. Gravel = 3 Parts x 140.8 cu. in. = 422.4 cu. in.
Total 844.8 cu. in.
NOTE: This technique will work for any kind of mixture (concrete, mortar, Hypertufa, pizza sauce, whatever) and regardless of how many components are involved.
Converting Component Volumes to Weight:
And, if you would like to convert the resulting Volume of each component into a weight you can measure out…here’s how to go about that.
First, convert cubic inches into cubic feet (since that’s how most materials weights are listed). To continue with this example, start by dividing the total cubic inches of each component by the volume of one square foot in cubic inches (12″x12″x12″= 1728 cu. in. per cubic foot).
a. Cement: 140.8 cu. in. divided by 1728 = 0.0814 cubic feet
b. Sand: 281.6 cu. in. divided by 1728 = 0.1629 cubic feet
c. Gravel: 422.4 cu. in. divided by 1728 = 0.2444 cubic feet
Now just multiply the value in cubic feet for each item, times that items “standard weight per cubic foot”*:
a. Cement: 0.0814 cubic feet x 94 pounds per cubic foot* = 7.65 pounds of Cement
b. Sand: 0.1629 cubic feet x 100 pounds per cubic foot*= 16.29 pounds of Sand
c. Gravel: 0. 2444 cubic feet x 95 pounds per cubic foot*= 23.22 pounds of Gravel
Now you can even predict approximately what the finished piece will weigh by adding up the totals, in this case…7.65 + 16.29 + 23.22 = 47.16 pounds (the only variable being the retained moisture content which will constantly be changing for most concrete).
*And where did I come up with those “standard weight per cubic foot” figures? Just check out the “Handy Measurement Equivalents & Weights” page, right here on this site. It displays many of the industry standard weights for the most common concrete & Hypertufa ingredients. Pretty neat, huh?
(Sorry, but for the Pizza Sauce weights, you’re on your own.)