If you’ve ever wanted to know what are contraction and expansion joints, this is the article for you. Expansion joints in any type of concrete control the location and spread of cracks. If a contractor tells you your concrete isn’t going to crack, he simply does not know what he’s talking about. All concrete cracks. The main job of a control joint is to specify where the crack should take place.
In the summer, when the temperature outside is very hot, concrete will expand. If there’s no room for the concrete to expand, it will crack within itself or against something else. When it’s cold outside, the concrete shrinks. Expansion joints are designed to give your concrete the flexibility it needs in order to expand and contract like it needs to.
Expansion joins come is several different ways. They can be hand-tooled or saw cut, made with treated lumber or blackboard, but more importantly, they should be made to a depth of no less than 1/4 of the total thickness of your concrete. If you have a 4″ slab, you should have an expansion joint at least 1″ deep. If your slab is 5″, it should be at least 1 1/4″ deep. Joints should be spaced no more than 10 feet apart for a 4 inch slab. Driveways that are wider, 12 feet or more, also require a joint down the center. Panels should be as square as possible, but in no case, should the long side be more than 1 1/2 times longer than the shorter side.
Jointing should begin as soon as possible after the finishing operations. If jointing is to be done with a hand groover, proceed when the concrete sustains foot pressure with only a 1/4″ inch indentation. If saw cutting, it should begin within 24 hours.