Chicago-area builders have been watching with great interest the progress of a prestressed lift-slab job in the west suburban town of Hinsdale. The structure is a combination rug cleaning plant, office, and store building with over-all dimensions of 60 by 160 feet. In the one-story section there is an 8 inch slab measuring 60 by 106 feet and a 7 and one-half inch slab measuring 27 by 46 feet, while the two story section consists of two 6 inch slabs measuring 54 by 60 feet. Prestressing was accomplished by post tensioning as soon as test cylinders reached the required strength of 4000 psi. Hand operated hydraulic jacks were used to stretch the cable strands as much as 9 inches to obtain the desired prestress. The lift slabs were separated from the base slabs by using two coats of a paraffin and oil base parting medium preparation over the base material, the two coats applied at right angles to assure complete coverage. According to the contractor this precaution not only made it possible to separate the slabs without trouble or damage, but also resulted in the virtual elimination of honeycombing. The material also serves as a curing compound. The sequential steps involved in the Hinsdale project included placing footings, erecting columns, casting ground floor slabs, then casting second floor and/or roof slabs using the grade floors as forms, post tensioning the lift slabs raising them by means of mechanical equipment, and finally securing the second floor and roof slabs to the columns by means of welding. It should be noted that prestressing is not a requirement of lift-slab method, although it has self-evident advantages in increasing economical span lengths and holding down required slab thickness.