Why is my Concrete Cracking?
Q & A about Concrete
|A freshly poured slab, waiting to be stamped|
A: This is kind of like asking what the difference is between flour and a cake. Cement is a component of concrete that causes it to harden. Concrete is the product we pour in wet form and dries into a solid material. So basically, Cement + Sand or gravel + Water = Concrete
Q: Will my concrete crack?
A: The sad but true answer is absolutely. All concrete hardens, turns gray and cracks – this is just the nature of the stuff. But the good news is that we can do a lot to minimize the cracking and keep the slab from heaving or shifting when it does crack.
Take a look at my video on stamped concrete patios to learn about good preparation by clicking the link below.
Q: My contractor said he is using 2,500 psi. What does this mean?
A: Concrete’s projected strength is rated in psi or pounds per square inch. This is rating given to a concrete recipe based on past tests with this mix. A certain mix may have more cement or other additives in it that make it stronger or make it cure faster. A hardened sample is pressed to see how much pressure it takes to fracture the sample. This same recipe is then duplicated at the plant when someone asks for concrete of this strength. I highly recommend using 3,000 or 3,500 psi concrete for residential slabs if you can afford it. It will pay you back by lasting longer.
Q: What is concrete’s Slump?
A: The slump is a measurement in inches that is used to describe how thick the concrete is. The wet concrete is placed in a small tub with a gate at one end. The gate is opened and a measurement is taken of how far the concrete “slumps” out of the trough. (It’s a little more complicated than this, but you get the idea.) The higher the number, the runnier and wetter the concrete. The lower the number, the stiffer the concrete. Most concrete delivered to job sites is 4” slump.
Q: How much concrete do I need for my job?
A: Concrete is measured and ordered by the cubic yard. This means measuring the area you intend to pour and doing the math.
A 12’ x 16’ patio that is 4” thick would look like this
12’ x 16’ x (4”/12”)
12’ x 16’ x 1/3 = 64 square feet
64 square feet divided by 27 square feet per square yard
64 ÷ 27 = 2.37 yards of cement
Q: What quantities can I order?
A: The smallest quantity that a plant will generally send out in a truck is 1 ½ cubic yards but you will have to call your local cement plant and ask them what their policy is. You can also expect to pay an additional short delivery fee of up to $100 for any order less than 5 yards.
Did I miss anything in this list?
Let me know and I’ll do my best to answer it.