HOW TO ESTIMATE HOW MUCH CONCRETE IS NEEDED FOR A JOB.
Ready Mix concrete is sold by the cubic yard. One cubic yard of concrete will fill a space that is one yard wide by one yard deep, by one yard high. Unfortunately, construction requirements are usually measured in feet or in inches, or often in a combination of the two. Of course, one yard is 3 feet, and one foot is 12 inches, so a reasonably clever person can convert the measured feet and inches into cubic yards. It helps to have some examples.
- First, let’s return to that one cubic yard box. It is also 3 feet by 3 feet by 3 feet. Remembering how to calculate volume, we multiply the length times the width times the height. To measure the cubic feet of this box, we take 3 times 3 times 3 (3*3*3=27 cubic feet). Therefore, one cubic yard of space is the same as 27 cubic feet of space, meaning 27 cubic feet of space will require one cubic yard of material in order to be filled.
- Now, if we measure everything in feet, we’ll be able to simply add up all the cubic feet of space, divide by 27 and know the required number of yards. However, often we know the length and width in feet, but the depth is measured in inches. Remember, there are 12 inches in a foot, so to convert inches into feet, we simply divide the number of inches by 12. Six inches divided by 12 is .5 feet. 8″/12= .667 feet. 4″ / 12 = .333 feet.
- Let’s portray this with another example; a slab that is 16′ x 20′ x 4″ deep, will need 16 x 20 x (4 / 12) = 106.667 cubic feet. Divide this by 27, and you need 3.95 yards. We sell concrete in quarter yard increments, so four yards are needed. Generally, savvy contractors add 5-10% for waste and spillage – so a prudent order here would be for 4.25 yards.
- Another way to estimate slabs is to calculate the square footage and then divide by a conversion factor for the depth of the slab. This is commonly done, and is the same thing mathematically, but easier for many people to remember. To use this method, calculate the square footage by measuring the length by the width, and divide by the appropriate conversion factor (see information in the accordion at the bottom titled “Thickness Conversion Factor“.
HOW TO PREPARE FOR A CONCRETE JOB.
- Generally speaking, when you place concrete you should check with your city building inspection department to learn what is required in terms of permits and inspections. Since concrete is a perishable product, waiting until the concrete arrives to find out that a permit is required can be an expensive learning experience.
- Have a plan. If you are working from a building plan, read the requirements carefully and follow them. If you are working from an idea in your head, commit it to paper, so you can communicate it to others and so you can be clear about what you intend to do.
- Form work. Concrete arrives as a flowable liquid. Within 90 minutes of mixing, concrete should be in its final place and waiting for the appropriate finishing steps. While in its liquid form, concrete exerts a huge amount of pressure on its form work. The requirements for form work vary according to the volume of concrete contained by the form and the height of the concrete. When it doubt, build form work heavy. It is much easier to build a sturdy form than to attempt to shore up a weak form during placement, or to clean up after a form has failed in the middle of placement.
- Ground/Soil Preparation. Concrete should be placed on undisturbed ground when possible. If this isn’t possible, placing concrete on well compacted and well drained subgrade is important. Concrete just 4″ deep weighs almost 50 pounds per square foot, so if it is placed on uncompacted fill, the concrete itself will compact the fill, and you may run short.
- Determine need for re-enforcement. Concrete is incredibly strong in compression. It takes great force to compress concrete – commonly used exterior mixes typically are able to resist more than 4000 pounds of compressive force per square inch before crushing. However, concrete is not particularly strong in either flexion or tension. If concrete will be subjected to either significant flexion or tension forces, you may need to use steel to re-enforce the concrete. The steel provides the strength to resist tension and flexion.
- Tools and crew requirements. There are many tools required for concrete finishing. Most neighborhood rental stores will be able to rent wheelbarrows, bullfloats, mags, trowels, edgers and jointers. Shovels, rakes and other tools will be required to move wet concrete. If you need to wheel the concrete, you will need 1-3 wheelbarrow operators and 1-2 people on the placement portion. To place several yards of sidewalk, for example, you may be fine with two wheel operators and one screeder (the person leveling the concrete). To place a garage may require two screeders and two more on wheelbarrows. For most placements, your spouse and 10 year old child are not enough help. When in doubt, call in several extra friends, provide some liquid refreshment and a bite to eat, and appreciate that the satisfaction and savings from doing the job yourself will be impossible to obtain if your crew isn’t big enough or lacks the skills to finish the concrete before it turns into a solid mass of rock.
CAN YOU DO THIS?
Read the accordion above if you haven’t already to see the minimum requirements for working with concrete. Installing concrete isn’t for everyone. There are many good contractors you can hire to place and finish your concrete. Do not underestimate the physical requirements of placing concrete. Bigger jobs require organization, a division of labor, competent direction and leadership skills. Because of this, we suggest that you start small. Learn on a small project, and work your way up to bigger projects, or find a friend who has a little more experience. Whatever you decide, make sure you have carefully thought through the requirements of the job and have a clear game plan to execute.
WHAT IS CURING?
Curing is maintaining sufficient temperature and moisture in concrete so that it can fully hydrate. Hydration is the chemical process that changes concrete from a sloppy liquid into a stone-like mass. 95% of hydration is complete in 28 days. However, if either the temperature drops below 40 degrees or the moisture drops below a certain level, hydration will cease before 28 days, and therefore, before the concrete reaches its full potential strength. Click here to learn more.
HOW TO SCHEDULE YOUR DELIVERY.
- Call us at least one day before you need concrete – please allow more time if the job is large or if you need special timing.
- We’ll need the delivery address, the intended use for the concrete, your name and at least a rough idea of how much you will need before you can reserve a delivery.
- Call dispatch at 612-789-4305 or stop in and visit us at our dispatch office in northeast Minneapolis – 2610 Marshall Street NE.
- We are happy to walk you through the ordering process so you are sure to get what you need.
THICKNESS CONVERSION FACTOR.
Example below is for creating a
32′ x 20′ concrete slab
Conversion Factor: 160
Equation: 32 x 20 / 160
Amount of Concrete: 4 yards
Conversion Factor: 108
Equation: 32 x 20 / 108
Amount of Concrete: 6 yards
Conversion Factor: 80
Equation: 32 x 20 / 80
Amount of Concrete: 8 yards
Conversion Factor: 65
Equation: 32 x 20 / 65
Amount of Concrete: 10 yards
Conversion Factor: 54
Equation: 32 x 20 / 54
Amount of Concrete: 12 yards
Conversion Factor: 40
Equation: 32 x 20 / 40
Amount of Concrete: 16 yards
Conversion Factor: 27
Equation: 32 x 20 / 27
Amount of Concrete: 24 yards