Designed and built immediately after the end of the war, Hall B of the Palazzo delle Esposizioni in Turin represents Nervi's first concrete opportunity to apply the principle of structural prefabrication, combining in a large-scale vaulted structure his highly personal use of ferrocement (wire mesh and small diameter steel rods embedded in a thin layer of cement) with the extensive use of prefabricated elements. It is also the first project that links Nervi to the great industrial clientele of Turin and Fiat. The Società del Palazzo delle Esposizioni, had commissioned the engineer Roberto Biscaretti di Ruffia to build on the remains of the Palazzo della Moda, designed in 1936 by Ettore Sottsass and then bombed, an exhibition hall to serve as a showcase for Turin's automobile industry. In 1947, Nervi e Bartoli won the competition by invitation and proposed two substantial variants to Biscaretti's design, which was based on a large apsidal hall: sloping side pillars, so as to widen the span of the vaulted ceiling, and, for the terminal apse, a thin lowered semi-dome as an alternative to a flat roof.
For the construction of the vault, Nervi designed prefabricated ferroconcrete wave elements, mounted on tubular reinforcement and made integral by reinforced concrete ribs cast along the ridges and recesses of the waves. Elegant fans each connect three arches of the wave roof to the inclined pillars. The apsidal semi-dome, on the other hand, is made of lozenge-shaped ferrocement tiles, which act as non-returnable formwork, like the ribbed pavilion roof over four inclined arches of the next and adjacent hall C (1949-50).
Inaugurated on 15 September 1948 and advertised as 'the most beautiful building Italy has ever built', Salon B attracted the attention of the international trade press as early as 1949, when it appeared on the cover of 'La technique des travaux'. Between 1953 and 1954, it was enlarged by five bays, which definitively obliterated the inner colonnaded garden. Between 1952 and 1953, Nervi worked out a project with architect Ettore Sottsass for a further extension with a 100 m span arch on the main front, but it was not followed up due to Sottsass' death in 1953. Resubmitted to the Società Torino Esposizioni in 1959 and approved by the building commission, it was shelved by the Company, which opted for a new underground hall designed by Riccardo Morandi.
