A vertical joint system for a substrate having an opposed major first and second surfaces, the joint system comprising: male and female joints (Jm, Jf) extending along opposite sides of the substrate, the male and female joints being non-symmetrical such that when the joints are engaged with each other several gaps or spaces are formed between the engaged joints, the male joint comprising a male protrusion (Pm) extending generally perpendicular from the first major surface toward the second major surface and a male recess (Rm) formed inboard of the male protrusion (Pm); the female joint (Jf) comprising a female protrusion (Pf) extending generally perpendicular from the second major surface toward the first major surface and a female recess (Rf) formed inboard of the female protrusion; wherein the male protrusion (Pm) having a transversely extending surface on a side distant the male recess (Rm) being an outer most side of the male joint, the male recess (Rm) having a transversely extending surface on a side distant the male protrusion (Pm) being an inner most side of the male joint, the female protrusion (Pf) having a transversely extending surface on a side distant the female recess being an outer most side of the female joint, the female recess (Rf) having a transversely extending surface on a side distant the female recess being an inner most side of the female joint; characterized in that the laterally spaced transversely extending surfaces (Cm1, Cm2, Cf1, Cf2) are curved convex surfaces configured to enable the male joint (Jm) of one substrate to engage the female joint (Jf) of a second substrate with the transversely extending surfaces (Cm1, Cm2) of the male joint located relative to the transversely extending surfaces (Cf1, Cf2) of the second joint to form respective first and second locking planes (18, 20) on the innermost and an outermost side of each joint, each locking plane lying parallel to the engagement direction and wherein the transversely extending surfaces associated with each locking plane extend laterally toward each other from opposites of the locking plane with the transversely extending surfaces (Cf1, Cf2) of the female joint overhanging the transversely extending surfaces (Cm1, Cm2) of the male joint; wherein two or more substrates with like joint systems are capable of engaging each other in response to a force applied in an engagement direction which is perpendicular to the major surfaces and subsequently disengaged by lifting a first substrate in a direction opposite the engagement direction to facilitate rotation of adjacent engaged substrates along opposite sides of the first substrate to lie in planes declined from the first substrate and subsequently applying a force in the engagement direction to the second joints of the engaged substrates. wherein the male protrusion (Pm) having a transversely extending surface on a side distant the male recess (Rm) being an outer most side of the male joint, the male recess (Rm) having a transversely extending surface on a side distant the male protrusion (Pm) being an inner most side of the male joint, the female protrusion (Pf) having a transversely extending surface on a side distant the female recess being an outer most side of the female joint, the female recess (Rf) having a transversely extending surface on a side distant the female recess being an inner most side of the female joint; characterized in that the laterally spaced transversely extending surfaces (Cm1, Cm2, Cf1, Cf2) are curved convex surfaces configured to enable the male joint (Jm) of one substrate to engage the female joint (Jf) of a second substrate with the transversely extending surfaces (Cm1, Cm2) of the male joint located relative to the transversely extending surfaces (Cf1, Cf2) of the second joint to form respective first and second locking planes (18, 20) on the innermost and an outermost side of each joint, each locking plane lying parallel to the engagement direction and wherein the transversely extending surfaces associated with each locking plane extend laterally toward each other from opposites of the locking plane with the transversely extending surfaces (Cf1, Cf2) of the female joint overhanging the transversely extending surfaces (Cm1, Cm2) of the male joint; wherein two or more substrates with like joint systems are capable of engaging each other in response to a force applied in an engagement direction which is perpendicular to the major surfaces and subsequently disengaged by lifting a first substrate in a direction opposite the engagement direction to facilitate rotation of adjacent engaged substrates along opposite sides of the first substrate to lie in planes declined from the first substrate and subsequently applying a force in the engagement direction to the second joints of the engaged substrates.