A heavy typhus fever on the Balearic Islands in the early 1920s brought the turning point from painting to writing.
At the Swiss National Exhibition of 1939 [de] in Zürich, the dialect drama Steibruch was premiered extremely successfully and later also made into a film.
He continued the critical questioning of the Swiss present with a number of extensive and unconventional novels.
In a large number of essays and speeches, Welti took a stand on cultural, literary, and political questions of his time.
The last work, Bild des Vaters (1962) is a sensitive artist's portrait, which finally put him at the same level with his father.