The direct cause of joint spalling in industrial floors is loading at the joint. The indirect cause is poorly constructed joints that don't adequately support the loads applied to the concrete. Four commonly used joint systems or fillers that can lead to spalling include left-in-place metal keys, plastic crack-inducing strips, elastomeric joint fillers, and high-strength epoxy fillers. When dowels are used to transfer loads across joints, they also must be installed properly.