Why Concrete Cracks and What Control Joints Do

Summary:

Cesar tells homeowners up front that concrete cracks, preferring honesty to a surprise later. Concrete shrinks as it cures and moves with the ground and with temperature, and when it can't move freely it relieves that stress somewhere. Control joints determine where. The lines cut into a driveway are not decorative; they give the slab a planned weak point so movement opens along a straight line instead of running an irregular crack across the surface. Slabs poured without joints, or with joints placed incorrectly, are where the ugly cracks appear. He also gives homeowners a way to judge their own concrete: a tight line following a joint is normal, while a crack wandering freely or with uneven sides signals a problem underneath.

Answer:

Concrete cracks. I tell everybody that up front, because I'd rather be honest than have somebody surprised a year later. It shrinks as it cures, and it moves with the ground and with the temperature, and when it can't move it relieves that somewhere. What we control is where. That's what the joints are for. Those lines you see cut into a driveway aren't decoration. We put them there so that when the slab does move, it opens up along that line instead of running some crooked crack across the middle of your driveway. When you see a slab with no joints in it, or joints that were put in the wrong places, that's when you get the ugly ones. So there's normal and there's not normal. A tight line following a joint is the slab doing exactly what we designed it to do. A crack running wherever it wants, or one where the two sides aren't level with each other anymore, that's telling you something happened underneath.