Elastomeric joint seal

Claim 1

A retractable inner form for a concrete mold assembly comprising a pair of adjacent wall sections bordering a hollow interior of the form and having corresponding outer surfaces arranged to form the inner contour of a concrete casting, the wall sections also having corresponding inner surfaces defining the hollow interior of the form, and laterally spaced apart pressureapplying edges each extending between a corresponding outer surface and a corresponding inner surface of the wall sections, a substantially non-porous, deformable elastomer between the pressure-applying edges of the wall sections forming a joint seal, the joint seal having a front surface extending substantially continuous with the outer surfaces of the adjacent wall sections, and opposite side edges extending inwardly from the front surface of the seal toward the hollow interior of the form, each side edge having a pressure-receiving portion engaged with a corresponding pressure-applying edge of the wall sections, whereby when a retracting force is applied to the wall sections of the inner form, pressure is exerted on the pressurereceiving portions of the joint seal to squeeze the seal and reduce the size of the inner form, the joint seal being of such cross-sectional shape and being engaged with the wall sections such that the pressure applied by the edges of the wall sections is induced eccentric to the centroid of the joint seal at such points of contact that a minor portion of the joint seal cross-sectional area extends between the front surface of the seal to the pressure-receiving portions thereof, and a major portion of the joint seal crosssectional area extends from said pressure-receiving portions inwardly toward the interior of the form remote from the front surface of the seal, the opposite side edges of the joint seal major portion being laterally spaced from the adjacent pressure-applying edges of the wall sections during normal retraction of the form to accommodate inward expansion of the joint seal when the wall sections are retracted so that the front surface of the seal is substantially prevented from bulging beyond the outer surfaces of the adjacent wall sections.