An interesting technique for site precasting of exposed aggregate panels has speeded the construction of a multi-story office building in Los Angeles. One of the keys to the method is a proprietary sealant. In the sequence of operations , a 3 /8 inch layer of white silica sand was first spread inside forms resting on a clean casting slab. Next the sealant was sprayed on the sand at the rate of 75 square feet per gallon. Prefabricated reinforcing was positioned on top of the sand and sized coarse aggregate was then pressed into the treated sand. When the material had acquired its initial set, lightweight concrete was placed to complete the full 8 inch thickness of the slabs. After screeding, the top surfaces of the panels were sprayed with the same sealant used to prevent the mortar from going through to the bottom faces of the panels. On the following day forms were jacked up and another panel was cast right on the first. When the panels were cured they were picked up with a crane and the exposure of the aggregate was completed by simply brooming or pressure hosing the sand from the exposed faces.