How to Make Concrete Control Joints

What You'll Need
Expansion joints
Cement saw
Jointing trowel
Wood slats

If you work with concrete you need to know how to make concrete control joints. They’re important in that they allow you to control any cracking that might occur in the concrete you’ve laid sue to changes in temperature. Unless you use concrete control joints the cracks will be random. By using concrete control joints you can fix where those cracks will occur.

Step 1 - Pouring

Concrete control joints, also known as expansion joints, are something best added when you’re pouring the concrete or before it cures. With a large area of concrete there will be a number of “pours” and so you can put in concrete control joints between each pour to allow for expansion. Typically these expansion joints are made of rubber or cork. If you have slats of wood that are sufficiently thin you can use these instead.

Step 2 - Setting in Place

When you pour a concrete path or driveway you’ll see slits between areas of concrete. These are the concrete control points. To put one in place, set it after the first pour to give a space before your second pour. Do the same after each pout and then leave the control points in place when the concrete dries.

Step 3 - Trowel

The jointing trowel is the tool specifically designed for creating control joints. If you’re not using expansion joints, you can slice into the concrete when it’s still wet to create room for expansion.

This can be a tricky operation, and you need to be experienced to make it look good. The best method is to take a piece of 2 inch by 4 inch lumber and lay it over the concrete to act as a guide. Now run your trowel into the concrete. The lumber will make for a straight edge. It’s notable that this method will work best when the concrete area isn’t especially wide. You’ll have good success using a trowel to create concrete control joints on a path or sidewalk, but not on a driveway.

Step 4 - Cement Saw

If a slab, such as a driveway, is partially hardened and has no concrete control joints, you can put them in with a cement saw. This will also work on hardened concrete. Note that it should only be used where no other type of concrete control joints have been installed in the concrete.

Put on safety equipment before starting up the saw. Wear safety goggles and gloves. Using a line and chalk, set a line across the concrete, making sure it’s straight and at 90 degrees to the edges. The depth of your cut will depend on the thickness of the concrete slab. With a think slab you should set the saw to cut at a depth of ¼ inch. With thicker slabs, cut down ½ inch. Go slowly to make sure you keep to the line you’ve drawn. Continue until you’ve cut across the entire slab. With a driveway you’ll require several concrete control joints.