What is the purpose of concrete joint filler?

Expansion joints

Expansion joints are a part of the concrete installation and are filled with a sponge rubber material at that time. These are joints that cannot be coated or sealed as part of the epoxy flooring system. These joints are designed to allow movement between two different pours of concrete. Typically, these will be around support columns or along supporting walls. If the joints are coated over with epoxy the flooring system will crack along this joint leading to early failure of the system.

Cold Joints

These joints delineate two different pours of concrete. Like expansion joints, cold joints allow for movement of the concrete. It is not recommended to coat over these joints as part of the floor coating system. After the installation is complete a flexible, elastomeric polyurethane joint filler can be applied to seal the flooring system which provides a clean, finished look.

Control joints

Also called saw cuts. These joints are added to a floor after the concrete has been poured. All concrete moves as a result of seasonal temperature changes. Saw cuts are designed so that if the concrete cracks, it is more likely to occur along these lines and making them less visible and damaging. These joints are filled with an epoxy patching material prior to installing the epoxy flooring system.

Different ways to fill concrete joints explained:

Concrete joint filler strips:

Foam backer rods are used in concrete joints if they are too deep. Elastomeric sealants are most effective when they adhere to the sides of a joint and not the bottom. By placing a foam backer material into the joint first it also helps to place less material into the joint.

Concrete joint filler machine:

Two component polyurea joint fillers are a hard curing filler used often times as part of a polished concrete system. This is also used if the concrete is left uncoated, but the joints need to be filled. This type of material sets up extremely fast and has about a 1- or 2-minute working time. These products are installed using a special caulk tube that mixes the material in the tip as its being squeezed out. However, for large projects this would not be very cost effective. So, companies like Graco, make a machine that draws the material from 5-gallon containers and mixes it through a specialized gun in real time during the installation process.

Concrete joint filler epoxy:

This is the 2-component patch filling epoxy used to fill all cracks, divots, rock pops, saw cuts or any other surface imperfection prior to installation of an epoxy system.

When or in what situation is it okay to DIY concrete joint filler, and when would it be better to contact a professional?

The products and equipment used are very specialized and not something found at the big box stores. It really depends on the level of knowledge a DIYer has with concrete, identifying the joint types, and knowing how to address them. Dealing with joints is part of our installation process and it can be very unlikely that someone would be attempting this on their own prior to us installing a floor. We don’t recommend filling concrete joints without a professional because if the wrong material is used, or if the wrong joint was filled, it can lead to early failure of an epoxy system.

Remember, an expansion joint is supposed to move. If a rigid epoxy is coated over the joint, the epoxy will crack, and just like ripping a piece of paper, it won’t happen in a straight, clean line just where the joint is. Often times the crack will splinter off at angles away from the joint, severely shortening the lifetime of the epoxy system.

Overall, if you are considering an epoxy floor and know that concrete joint filler is something you will need, contact our experts at SwedeBro for a free estimate on your project!