If you have concrete, you have cracks. They are inevitable features of the medium.
While cracking can be minimized through proper timing and technique, there’s nothing that can be done to prevent it completely.
Cracking occurs because concrete naturally expands and contracts with temperature and moisture changes. Cracks don’t harm the integrity of the concrete, necessarily, but they can be unsightly if not controlled.
Experienced concrete installers like those at Custom Concrete Contracting use control joints to prevent random and unplanned cracks. What these joints do, essentially, is ensure that most cracks will occur at the location of the joint and not elsewhere in the concrete slab. You’ll see these contraction and expansion joints in sidewalks, driveways, warehouse floors and even concrete roadways.
Contraction joints are cut or tooled into the concrete surface and actually serve to weaken the concrete along that line, so that when the concrete contracts, it will separate slightly at that spot. The concrete cracks under the pre-existing joint, so this crack is not visible from the surface. Such planned cracks allow concrete installers to choose the locations of inevitable contraction cracks, and since the cracks are below the surface of the concrete, the concrete can crack as it needs to without marring the finished look. The standard is to place contraction joints at intervals based on the thickness of the concrete (at intervals of roughly 24 to 36 times the thickness) and at a depth of one-fourth of the thickness. For example, a 6-inch slab would have joints every 12 feet or so, with those joints being 1.5 inches deep.
Learn more: Answers to common concrete questions
Expansion joints, similarly, exist to prevent expansion from buckling the concrete. Expansion joints (also called isolation joints) allow space for concrete to expand against walls, columns, curbs, light posts, other concrete slabs and any other object that could restrain the movement of the concrete. If concrete were to be installed tight against other materials, any expansion of the concrete could result in cracking. Contraction joints in pavement typically serve as expansion joints, too, since during concrete shrinkage the joints open enough to provide space for any future expansion.
For more information about Custom Concrete Contracting’s flatwork installation expertise in Whatcom and Skagit counties, please reach out to us or browse your website. Here’s an overview article all about pervious concrete.