A formed contraction joint in concrete is a type of joint that is created by installing a pre-formed joint material into the surface of the concrete. The purpose of a formed contraction joint is similar to that of a saw-cut or tooled contraction joint, which is to control cracking that can occur in concrete due to shrinkage and expansion.
Formed contraction joints are typically used in smaller concrete surfaces, such as sidewalks, patios, and driveways. They can also be used in larger concrete surfaces, such as industrial floors, where a straight-line joint is required.
To create a formed contraction joint in concrete, follow these steps:
- Wait for the concrete to cure: It is important to wait until the concrete has cured sufficiently before creating contraction joints. This typically takes about 4-6 hours, but can vary depending on the temperature and humidity.
- Determine the location and spacing of the joints: The location and spacing of the joints will depend on a variety of factors, including the thickness of the concrete, the expected temperature changes, and the type of traffic that will be using the surface.
- Install the joint material: Cut the joint material to the desired length and insert it into the surface of the concrete at the desired location. The joint material should be pushed down into the concrete to a depth of at least one-fourth the thickness of the concrete.
- Smooth and finish the joint: Use a finishing tool, such as a trowel or jointer, to smooth and finish the joint.
- Clean up the joints: Use a broom or compressed air to remove any debris from the joint.
By following these steps, you can create formed contraction joints that will help to prevent cracking and prolong the life of your concrete surface.
