SUNDEK’s Approach to Concrete Expansion Joints

How we treat expansion joints to allow proper surface movement and prevent coating damage.
Posted by admin on May 13, 2025 in Blog

Expansion joints are critical to the health of your concrete slab and coating.

Properly placed expansion joints are critical to the long-term durability of a concrete slab. Expansion joints are essentially small spaces or gaps placed between sections of concrete that allow for the concrete to expand and contract with temperature changes. Without expansion joints, concrete will crack as it moves.

Expansion Joints and Coatings

Even if you know your concrete slab will be resurfaced with a coating, expansion joints are necessary. A decorative coating won’t prevent cracking, and the success of the coating depends on the quality of the concrete slab.

How Does SUNDEK Deal with Expansion Joints?

Since our job is to install our coatings on top of existing concrete surfaces, our clients are often curious how we deal with expansion joints. We do not fill in or cover up expansion joints. Rather, we honor the joints to allow for proper deck movement and prevent random cracking. The expansion joints remain at the same width and depth during our coating process.

When necessary, we apply the finish coat system to the joint so that it matches the look of the rest of the surface.

Can SUNDEK Add Expansion Joints?

Yes. Before installing our coatings, we always thoroughly inspect the surface to make sure it’s able to accept and support a coating. If the surface appears to be lacking in proper expansion joints, we can add them. However, it’s important to keep in mind that the best time to add expansion joints is as soon as the slab hardens.

Expansion Joint Tips

When a concrete slab is installed, here are some guidelines to keep in mind:

Timing. Joints should be cut during the finishing stage. If the concrete sets before expansion joints are placed, a wet cut saw is required.
Spacing. Joints should be spaced (in feet) no more than two to three times the thickness of the slab (in inches). So, for example, a 4-inch slab should have joints that are 8 to 12 feet apart at a minimum.
Depth. Joints should be cut 1/4 of the depth of the slab. For example, a 4-inch slab should have 1-inch deep joints.
Placement. Joints should be placed in a pattern so that they are equally spaced.

For successful expansion joints, plan ahead and map out the expansion joints before beginning to place them.

Learn more about Joint Treatments in Sundek Applications.

Learn more about expansion joints in this whitepaper.

How Does SUNDEK Deal with Cracking Surfaces?

If your surface is already cracking and you’re not sure if it can support a coating, contact us to come out and take a look at your site. As long as your surface is structurally viable, we can resurface it. Learn more about how we repair cracked concrete.