During his studies at the Academy of Fine Arts in Antwerp, Mendelson took classes with Gustav van de Woestijne and Isidore Opsomer and got introduced to ruling animism. He took part in the salons Apport organised by Robert Delevoy and was in 1945, the year where he moved to Brussels, one of the founding member of the Jeune Peinture Belge. As of 1948 his work evolved to geometric abstraction. In 1951 he became a teacher in screen printing at the school of La Cambre. He was interested in the relation of painting and architecture and designed two projects for architectural integration (Kursaal, Ostend, 1952 – Hotel Canterbury, Brussels, 1953) and was co-signer of the manifest of the group Espace. He went to Spain for the first time in 1953, a country that made a deep impression on him. In 1956 he began a manneristic period and a return to figuration, which later on resulted in aquarelle (1967) and sculptures (since 1969). From early 1990 he returned back to abstraction with monochrome canvases.