Cerfix Procover Fix joint covers allow horizontal movements. Made of aluminum, they are flat in shape and come in two versions: One to be used between two surfaces of the same level (GJA/) and one to be used as a joint between a wall and a floor (GWA/). These structural joint covers are the best choice for compensating structural movements (that is, expansion and contraction) in two load-bearing surfaces while also hiding any cutting or installation imperfections.