2001 13th Ave N, St. Petersburg, FL 33713

How to Do Concrete

Calculating – Specifying – Ordering – Pumping – Prior Pour Check List
(Part 3 of 4)

 

Now that your planning is complete and your forms are in place, we suggest you review the type and amount of concrete you will need.​

Calculating the Amount of Concrete

This DIY Concrete Guide will show you how to order concrete and calculate your concrete order. The simple way is to call Carroll’s Building Materials and give us your measurements Length, (Width and desired Depth of the Slab). Another way to calculate the amount is to multiply the length of the slab by the Width of the slab then divide by the appropriate number correlating the depth from the chart below then round up to the next quarter yard. Remember we only charge for what you use rounded up to the next ¼ yard which is the industry standard. So if you are not sure and you want to order a couple more yards that’s ok. However, please don’t over order and specify 10 yards for a 2 yard pour because of the scheduling issues this creates.

Specifying Mix Design
Specifying the correct mix for your job is very important. Concrete specifications consist of Strength (PSI), Slump (basically the thickness), Fiber Mesh, Chemical Additives and whether you require a Concrete Pump. 80% of all concrete poured in Florida is 3000 Psi slab mix or 3000 psi pump mix. Other mixes are also available i.e. 3000 Psi – 5000 Psi mixes, Fine Grout, C-476 Cell and Flowable Fill. All mixes are also available using White Portland, please specify when you order. Below we will cover these specifications:

Specifications
Compressive Strength
Compressive strength must be specified at the time of ordering. (ie. 3000 psi, 3500 psi, 4000 psi, 4500 psi and 5000 psi). More psi = more strength and durability. (Also Note: the higher the PSI the shorter the set time will be.) Typically 80% of the slabs in Florida will be 3000 psi.

Slump
For our tropical environment we recommend a slump of 5-6 inches (+/- 1″). Note: a slump greater than 6″ may prolong the time you have to wait before finishing, particularly in cool weather. It will also increase the tendency for shrinkage cracking. Unless specified all mixes will be delivered at a 5” slump, unless it is going to be pumped in that case we recommend a 5” – 6” slump.

Reinforcing Wire Mesh & Fiber Mesh
When concrete cures the water in the concrete will begin to bleed off as it does the slab will start to shrink just slightly, as it shrinks cracks can form as the slab moves across the base material. These cracks are called shrinkage crack. Using reinforcement such as wire mesh, rebar, or fibers will not prevent cracks. It will, however, hold the concrete together when it does crack and prevent separation or vertical displacement.

While not always required in all counties for sidewalks and driveways, placing wire or fiber mesh in the slab it is highly recommended.

Fiber mesh
Fiber mesh can be used to replace wire mesh in most instances, except the first 15’ apron of a driveway. (Check your local codes) Reinforcing wire mesh is placed in the slab area prior to the pour the wire mesh is placed on mesh-ups which are 2” plastic chairs designed for wire mesh. (Shown Above Left) Wire that sits on the ground and is not kept in the middle of the slab by mesh-ups will do nothing for shrinkage cracks. Fiber mesh is added into the mix at the time of the pour and is much easier to work with. Most contractors only put in one or the other however, it never hurts to use both, and the additional cost is minimal.

Chemical Additives
In addition to air entraining admixtures, chemical additives may be used to accelerate or retard setting, reduce water or plasticize the concrete. Concrete Exposed to freezing and thawing temperatures should have a minimum compressive strength of 3000 psi and have at least 5% entrained air (+/- 1.5%). Air entrainment allows for the expanded water when frozen to travel into the air voids created by the air additive. Without the air, concrete is at risk for cracking. In Tampa Bay, freeze and thaw cycles are not normally a problem; however, we do include Air Entrainment in all mixes as a finishing and pumping aid.

To Pump or Not to Pumping Concrete
Another thing to consider when learning how to order concrete is to decide whether or not you need a concrete pump. Our Concrete Line Pumps are used when the job is in a hard to reach area that a concrete truck cannot reach with a chute, such as going around a home, buildings, through a building, over tall walls, pouring lintels, etc. We carry 200′ feet of hose (unless specified) and there is a $1.00/ft charge for any length over 200 feet. Some smaller jobs can be wheelbarrowed to save money on the pump, but keep in mind that it is extremely strenuous to try to wheelbarrow and to finish concrete at the same time. We recommend that you have extra help on hand, if you plan on wheelbarrowing a job.

Advantages of Using Concrete Pumps

Ordering Concrete

This is the best part. Call Carroll’s Building Materials, then ask for concrete dispatch. You will need the following information:

Note: Concrete Dispatch will call the night before the pour to confirm your delivery, and make sure you are ready to go. 

Do It Yourself check List Prior to Pour