Pablo Picasso, who has used materials ranging from fish skeletons to steel plates to express his artistic ideas, selected concrete for his latest American work- prestressed, post-tensioned and sand-blasted. Picasso entrusted the task to Carl Nesjar, and a Swiss contracting firm of A. G. Betograve. Construction began when workmen stripped the 4 feet of earth atop the garage and built a beam and slab foundation platform over the roof slab to distribute the sculpture's weight. Placement of reinforcing bars and post-tensioning tendons that formed the sculpture's "skeleton" followed. The tendons used consist of parallel-lay one-quarter inch diameter wires with positive end anchorage provided by cold-formed button heads threaded through the end anchorages. Coated tendons were shop-coated with a rust-inhibiting, low-friction, mineral-oil base grease and are spirally wrapped with a double layer of asphalt impregnated, fiberglass reinforced kraft paper to form the slippage sheathing. This coating provides permanent protection and lubrication and prevents concrete bonding to the tendons. A temporary wood scaffolding was then built to hold the tendons accurately in place. The "Betograve" method of concrete placement used by Nesjar for the sculpture involves two steps. First, the entire form was filled with black basalt pebbles, imported from Norway, using pails as a pulley arrangement. The aggregate was then vibrated to ensure maximum density. Very liquid grout containing chemicals to prevent shrinkage was then injected under pressure through ports near the base of the forms. The slowly rising grout filled the spaces between the aggregate and, as the bonding agent, formed a "skin" that completely covered the aggregate. Concrete was placed only to the first stressing elevation. After the concrete was set and the forms stripped, Nesjar drew the outline of Sylvette's profile on the buff slab, first with charcoal and then with wax crayon, adjusting the drawing to the scale of the massive sculpture. The details were then sandblasted free hand into the concrete surface, exposing the aggregate beneath.