Frequently Asked Questions

How is concrete made?

Concrete is a proportioned mix of sand, gravel, water, portland cement, and various additives depending on your region and the time of year. Concrete is perishable - once it is 'slumped', or mixed together, concrete will become unworkable in 3 to 6 hours without any accelerators or retarders. Adding water at the jobsite to make the concrete more workable is a standard practice in the industry; however, excessive water will weaken the concrete.

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How long should concrete last?

A standard residential 3000PSI exterior concrete driveway, under normal wear and tear in our temperate Georgia climate, should last your lifetime. We would say 30-50 years is a reasonable service life for a concrete driveway or patio. We've seen eighty year old concrete parking lots still in servicable shape. Concrete's life span is usually shortened not by its inherent PSI strength but by environmental factors such as tree roots, excessive loads, erosion, and sinking or movement of the sub-grade below.

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What causes concrete to crack?

Many factors may cause concrete to crack. Here are some of the most common reasons:

DRYING SHRINKAGE. New poured concrete shrinks just a little bit as it dries, especially when poured over a plastic vapor barrier, a common practice with concrete slabs for residential housing construction.

CONCRETE TOO WEAK OR TOO THIN. If not poured with the correct PSI or the correct depth, concrete might develop unexpected cracks due to its sheer weight.

TOO MUCH WATER. Too much water will overhydrate and weaken the concrete mix by creating excess voids. How much is too much? An expert will know. Only put as much water in the concrete as you need.

INSUFFICIENT CONTROL/EXPANSION JOINTS. You will know how much your contractor knows about basic concrete construction by asking him or her about control and expansion joints. They should be spaced about the same as the width of the pour up to about a maximum of twelve feet in width. This rule is just a guideline, and would change if your councrete pour has footings, rebar or wire, or is thicker than 4 inches.

JOINTS IN THE WRONG PLACE. An experienced concrete installer knows the math about where to put expansion and control joints, and also knows that it is an art. Joints need to be placed at building corners and turns, weak spots, over culvert pipes, etc..

EXCESSIVE WEIGHT ON CONCRETE. Most residential driveways aren't designed for weight exceeding a light truck.

NOTHING. That may sound weird, but sometimes concrete just cracks. We can only predict and attempt to control concrete cracks, but concrete itself always has the final say on where cracks appear.

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How thick should concrete be?

Concrete driveways, patios, and sidewalks should be a minimum of 3 1/2 to 4 1/2 inches thick. Any less and your concrete will crack where it shouldn't; Any more and you might be wasting your money, unless you have a good reason to thicken it. Commercial concrete parking lots start around 6" thick and airport runways can be as thick as 20" to 24" thick.

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What should I do about cracks in my old concrete?

Well, how much do you want to spend? To start with, there is no method to "reconnect" two broken concrete sections so they behave as one uniform concrete piece. This differs from asphalt, which bends with time. You can buy specially-formulated caulk that will prevent water from entering and seeping below a driveway, walkway, or patio - something that would be beneficial if you live in a climate with a significant frost line. But what about concrete resurfacing? Broken concrete pieces will always move independently of one another; that means any cracks below a resurfaced area will eventually transfer up through the new surface. That only leaves one thing. If you can't live with the cracks, you have to tear up the whole section and replace it with new concrete. The size of the concrete section would depend on the layout of your driveway, concrete patio, or slab.

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Should I have rebar, wire mesh, or fiber mesh in my concrete?

Concrete reinforcement is not a bad idea. Concrete reinforcement is not required in Georgia unless you are pouring a concrete slab or foundation, and most concrete driveways and patios don't have any reinforcement because it isn't necessary if the sub-grade of the concrete is stable. Be sure to ask your concrete contractor how much more it will cost to add a little rebar or some fiber and I'll think you'll be surprised how inexpensive it can be. It can definitely be worth the extra cost.

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Which is better - wire mesh or fiber mesh?

Nobody in the concrete installation business likes wire mesh. Wire mesh can be cumbersome, heavy, difficult and dangerous to unroll, unforgiving, and impossible to place consistently in the correct place within the concrete mix. The plain truth is no matter how good a concrete finisher is, most wire mesh is left underneath the concrete, not in it. Fiber mesh on the other hand, costs about the same and carries none of the above characteristics. Fiber mesh is light, easy to place, not dangerous, and it is mixed evenly throughout the concrete because it is installed in the concrete mix before the pour. Needless to say, we prefer fiber mesh. Your local building department might like it better, too.

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What is concrete resurfacing and would it work on my project?

Concrete resurfacing is the process by which a thin coat of specialized cement is laid on top of an existing concrete surface in an attempt to rejuvenate the old surface. Resurfacing, if done correctly, can last several years and can theoretically provide a durable new surface. Unfortunately resurfacing does not prevent, hide, or erase cracks, and any concrete cracks that lay below the newly resurfaced area will soon reappear. Only an expert can tell you if resurfacing is right for you. You may be surprised how similar the costs can compare with concrete resurfacing and complete concrete replacement.

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What are control/expansion/tension joints and where should they be?

Concrete will crack over time. Concrete control joints are either hand tooled, saw-cut, or keyway lines in the concrete that provide a weak area across the concrete to release tension caused by shrinking, movement, etc. In other words, these joints give the concrete a place to crack. Control joints if done correctly should be spaced about one and a half times the narrower width of the concrete up to twelve feet apart. Control lines should be spaced no farther than 12 to 14 feet apart in every direction for driveways and patios.

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How much weight is concrete designed to hold?

The rule of thumb we use is that a standard 3000 PSI residential driveway would support up to 2000-2500 lbs per tire(that's our opinion). Driveways could certainly hold more but may not be guaranteed to more than that. Our company routinely backs 50,000 lb concrete trucks up a driveway if the action is judged safe by a foreman. REMEMBER: A concrete or asphalt driveway is only as strong as the subgrade, or the ground below that supports it. If you can see empty space underneath your concrete, or you can tell that your driveway or concrete slab has lifted up (due to tree roots), or the ground below has settled or eroded, then your concrete may not perform as promised.

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What is PSI and how much of it should concrete have?

PSI stands for "Pounds per Square Inch" and refers to the inherent load bearing capacity or strength of the concrete. Concrete can be batched as low as 2500 PSI but most concrete applications such as driveways, concrete patios, and walkways and the like start at 3000 PSI and go up from there. The higher the PSI in the mix the stronger and more expensive the concrete will be. So, how much PSI is enough? We recommend 3000 PSI concrete for our standard driveways, walkways, and patios. Even footers and concrete foundations are routinely done with 3000 PSI concrete mixes. More intemperate climates may require 4000 PSI. The best advice is to call your local county building department and ask an inspector what they think - Be careful not to open a pandora's box, though.

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How long does concrete take to dry?

In general, after concrete leaves the mixing truck, concrete will dry to the touch in about six hours, although the drying time will vary with concrete's slump, ambient temperature, moisture content of the sub-grade, finishing method, and entrained admixtures. Within 8-24 hours you should be able to walk on your new concrete, although dogs should be kept off the concrete for another day or two. We recommend that you wait to drive a vehicle on new concrete for a minimum of three days after the concrete is poured. New concrete can hold your car after three days, but still has a long way to go before it achieves full strength, or what engineers call "28 day strength", which (surprise!) concrete will achieve in about one month. New concrete will continue to get stronger for months and even years after it is poured.

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What is the best time of year to pour concrete?

Concrete is best poured when the ambient temperature is between 45 degrees F and 85 degrees F. The closer you are to 45 degrees F the day of the concrete pour the longer concrete will take to dry (hydrate). In winter, most concrete installers use an accelerator such as calcium chloride that will build heat in the concrete mix and speed up the hydrating process. Non-chloride accelerators are used for colored and stamped concrete as well, although they are usually more expensive. In the summer, many concrete installers use a retarder to slow the concrete mix as it hydrates.

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What is a concrete accelerator and a concrete retarder?

Concrete admixtures such as accelerators and retarders can both speed up and slow down the process of hydration (drying) in the concrete. Concrete accelerators, namely Calcium Chloride, achieves this by building heat when it is added to the mix, and this heat acts as a catalyst to speed up hydration. Concrete retarders do the opposite.

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