The joint gap is the distance between the electrofusion fitting and the pipe material. When no joint gap is present, the resulting joint strength is high but not maximum. As joint gap increases, the joint strength increases to a point, then begins to decline fairly sharply. At larger gaps sufficient pressure cannot build during the fusion time, and the joint strength is low. The effect of joint gap on strength is why the scraping of the pipes before welding is a critical step. Uneven or inconsistent scraping can result in areas where the joint gap is large, leading to low joint strength.