Above all, he was closely attentive to the work done in churches in Switzerland from 1924 to 1935 by Gino Severini; he admired not only Severini’s attempt to integrate stylistically the great examples of the Italian wall painting tradition - Fra Angelico and Masaccio - with the Purism of Denis and a moderate Cubism, as well as his ideological intent to create a public art.

Answering a questionnaire from the magazine Domus, in which Sassu proclaimed his realism, on the subject of wall painting he stated that this is a "fundamental fact for the rebirth of art in its social function."

In 1948 he created the oil mural Cronache di Albisola, painted on panels, portraying the people who shared with him his artistic experience in the Ligurian town. Essentially a response to the demand expressed in the Manifesto del realismo of 1946 for "walls" and "blocks of stone" to create a new art capable of communicating with a wider general public is provided by the fresco The Mine. Painted in 1950 for the guest quarters of the mines at Monteponi in Sardinia, it unites in a narrative tone a Mediterranean landscape populated by mythical figures with an industrial scene.

Other examples are The Myth of Prometeus of 1954, executed in the artist’s house at Albisola and now in the Palazzo della Provincia of Sassari; The Liberators of 1956, now in the Museo Gramsci in Ghilarza; La pace of 1958, a tempera painted for the Casa del Popolo at Valenza Po; The Angevis Uprising of 1962, a painting in silicon and mosaic relief for the elementary school in Thiesi, and finally his recent frescoes in his house on Majorca with Arcadian and mythological subjects.