Measuring Concrete

      

FIGURING CUBIC FOOTAGE:
The biggest problem for the nonprofessional is figuring the amount of concrete needed and then figuring the amount of materials or ingredients needed to make up the concrete. Here are several tips to make the job go easier:

Measure the inside of the form and then convert all dimensions to inches. Multiply the width times the length times the height or depth of the concrete depending on whether the placement is a slab or wall. This will provide the cubic volume in inches. To get cubic feet, divide this figure by 1,728. Multiply the length times the width of the slab. Then refer to the amount given for the depth of slab. The table gives the amounts for 1 cubic foot. Multiply the proportions for each material by the amounts given in the table. The result will give you a good idea of the amounts needed of each component material.

If you are building a large patio or driveway, you should work in terms of cubic yards. To convert from cubic feet, divide the footage by 27. It's a good idea to plan for more concrete than you need. The amount of extra material depends on the project. Plan for between 10 and 15 percent for walls and footings and 20 percent for slabs.

It's a good idea to plan for more concrete than you need. The amount of extra material depends on the project. Plan for between 10 and 15 percent for walls and footings and 20 percent for slabs.

MEASUREMENT TECHNIQUES:
Once you have determined the amount of concrete needed, the next step is to determine how much of the different materials you will need--if you are mixing the concrete yourself.

Volume method-
This is perhaps the easiest method. Use a shovel to move the cement, sand, and gravel into the mixing location and then just count the shovelfuls. If you're using a power mixer, turn on the mixer and throw in the shovelfuls. The dry materials will mix together as you go.

Weight method-
Use a specially marked bucket. Weigh the bucket and then determine a set weight such as 10 pounds. Weigh each ingredient separately and make an identifying mark for the level of 10 pounds for each ingredient. Then just count the bucketfuls as you put the correct proportions into the mixing container. Cement: red; sand: yellow; gravel: green.

Adding water-
Measure the amount of water you add. If you get too much water and do not have enough cement to add to it to correct the situation, you can ruin an entire batch of concrete. Use a bucket that has a known capacity so you can make an accurate measurement.

The strength of the concrete will depend on the amount of water used. If too little water is used, there won't be enough to provide a good fluid state that can be worked easily and will ensure that each and every solid particle is coated and bonded. You should use as much water as possible without creating a problem with the workability and smoothness of the concrete. Too much water results in concrete that is unworkable and hard to set up. The cement particles will float up to the surface and, worst of all, weaken the concrete.

As a rule of thumb, professional masons consider 6 to 7 gallons of water the correct amount of water per bag of cement, depending on the dampness of the sand the size of the aggregate.

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