Bottom Slab Home » Bottom Slab Engineered Bottom Slabs for Maximum Performance SIZE TYPE THICKNESS 3' O.D. Concrete 4", 6" & custom 4' O.D. Concrete 4", 6", 8" & custom 6' O.D. Concrete 4", 6", 8" & custom 8' O.D. Concrete 6", 8", 10" & custom 10' O.D. Concrete 6", 8", 10" & custom 12' O.D. Concrete 6", 8", 10" & custom