The evolution of plaza waterproofing in America

Plazas over occupied spaces proliferated when they became feasible for below-grade activities. Their usage was spurred by the advent of air-conditioning and city incentives for open spaces. Coal tar pitch waterproofing membranes, which had provided reliable waterproofing with split slab construction, fell out of favour as a result of the shortage of coke, the labour-intensive application costs, and the imposition of stringent VOC requirements. Asphalt-based substitutes failed to perform because differential movement of the wearing courses imposed stresses beyond their capabilities. As a result, investigators recommended divorcing wearing surfaces from drainage courses and later insulation layers. This freed waterproofing manufacturers from the need to develop membranes that could absorb the shear stresses that destroyed multiple-ply asphalt systems. After World War II, advances in polymer chemistry fostered the development of liquid-applied membranes. These, along with imported elastomeric sheets from Europe and rubberised asphalt from Canada, revolutionised the plaza waterproofing industry.