Concrete Construction: Joint Placement Guide

Pouring concrete is both an art and a science. When concrete is poured, it is in a viscous liquid state that takes shape of whatever it’s put in. As it dries, concrete shrinks, creating cracks and fissures that go beyond the surface.  

Despite your best efforts to prevent it, cracking can and will occur. If left unchecked, small cracks can grow, creating eyesores and degrading property value.  

In addition to finding concrete forms for sale, you need the proper tools to place joints in your pour. Placing contraction or control joints gives you greater control of how the concrete cracks as it shrinks, creating straight lines instead of random breaks. 

Prevent and Control Cracks 

Controlling cracking is critical for solid structural behavior. There are two primary ways to do this — placing joints or using steel reinforcement.  

Putting steel reinforcement in the slab holds random cracks tightly. The downside, however, is that they can also increase the potential for hairline cracks to pop up in the exposed concrete surface.  

Joint placement gives you greater control over how cracks occur. They’re added to predetermined locations so that concrete cracks in a straight line over weakened planes. Doing so ensures cracks stay below the finished surface, enhancing the visual appeal of the slab.  

Tips for Joint Implementation 

There are three ways to form contraction joints: saw cutting, a grooving tool, or by inserting a plastic strip where the desired division will be. Proper timing and joint depth are very important measures to keep in mind—otherwise, the joints you create may be rendered useless.  

In hot weather, cracking can start within 6-12 hours. It’s best to apply a joint before that window starts. If you’re planning to insert a contraction joint within the first couple of hours, make sure to use an early-entry saw because most other tool’s aren’t built to work with hardening cement.  

Proper spacing determines the effectiveness of a joint. A good rule of thumb is to keep joints twice as deep as the thickness of the concrete slab. For instance, a slab 3’ thick should have a joint 6’ apart from the last.  

It’s important to cut a joint ¼ of the thickness. For example, on a sidewalk, if the slab was 4” make sure to cut your joints to be 1” deep. 

Start Right to End Well 

Contraction/control joints are essential to laying concrete, but unfortunately, are often overlooked. They are not laid out in initial building plans, and builders sometimes insert them when and where they feel like it.  

This leads to a degradation in the quality of the build and the structural integrity of whatever the concrete is reinforcing. The best way to avoid that is to introduce control joints properly and with consistency to keep your pour secure and safe from damage.  

If you are looking for concrete forms, or need experts in concrete application, Forming America has you covered. We sell, rent, and renovate formwork, and ship all the equipment you need right to the jobsite. Give us a call today at 1-888-993-1304.