An Introduction To The Art Of Concrete Sawing

Most people recognize the ubiquitous and indispensable role that concrete plays in the modern world. Responsible for the building of our streets, homes, and workplaces, it is safe to say that it would be very difficult--if not impossible--to live without concrete. Yet many people remain ignorant about how concrete takes on its final form.

Concrete sawing is one of the most common concrete installation techniques, being a key step in ensuring that fresh concrete cures safely and predictably. Whether you are considering a job in the construction industry, or are simply a curious amateur, read on. This article will provide you with a useful introduction to the art of concrete sawing.

The principal goal of concrete sawing is to prevent the formation of cracks on the surface of a concrete slab as it cures. Accomplishing this goal involves the cutting of so-called control joints. Control joints act to relieve the shrinkage pressures that form as water evaporates out of the surface of the concrete.

In order to grasp how and why control joints work, it will help to understand a bit more about the curing process. Curing involves a chemical reaction that takes place between cement and water, forming a dense network of rock hard crystals as a result. Because this reaction proceeds at a relatively slow pace, however, evaporation tends to reduce the hydration at the surface of the concrete.

As the top of the concrete dries out, internal forces mount. Eventually, these forces will become great enough to overcome the tensile strength of the concrete, causing it to pull apart from itself. This results in the formation of what is known as plastic shrinkage cracks. Such cracks will permanently mar the appearance of the resulting surface.

Control joints prevent the formation of shrinkage cracks by providing the concrete with a place to pull away from itself without causing any cracking or other structural disruption. These joints are created using concrete saws. There are two main types of concrete saws used for this purpose. The first are large, push-behind saws.

A push behind saw looks somewhat like a giant lawnmower. As its name would imply, an operator walks behind it, while a saw blade mounted on the bottom cuts a control joint of a specific depth. The other type of concrete saw is known as a cut-off saw and closely resembles a handheld circular saw.

As you can imagine, sawing through concrete--even fresh concrete--is incredibly hard on a saw blade. Ordinary saw blades would wear down in a matter of minutes. To withstand such harsh usage, concrete saws generally come equipped with unique diamond-tipped blades, which are capable of withstanding the abuses of concrete for a much greater period of time.

Creating control joints with a concrete saw is only effective if you do it within a critical window of time. Should the cut be made too soon--in other words, while the concrete is too wet--often results in joint raveling. This refers to the phenomenon by which the inside edges of the joint will slump and crumble, resulting in joints with an unsightly, ragged appearance every bit as undesirable as the shrinkage cracks that the joint was meant to prevent.

Waiting too long before cutting control joints can create just as many problems. Cutting through overly hardened concrete will often result in stress fractures and cracking of its own. For these reasons, understanding the dynamics of curing concrete is one of the most subtle and crucial skills a concrete contractor can possess.

The ideal cutting time is not the same for every concrete surface. On the contrary, a contractor must take into account such factors as the weather, the humidity, the composition of the concrete mix, and the curing method you're using. In general, concrete sawing must be accomplished within a window 4 to 12 hours after you poured the concrete.