The effect of marbles and granites on the plasticity and bending stress of two Mozambican clays (OUA and CIMOC) was studied. For that purpose, clay masseswith addition of marble and granite rejects have been prepared, their plasticity and mechanical strength determined. While CIMOC clay results showed a non-regular behaviour, OUA clay, clay with high plasticity, exhibited a regular decrease of plasticity with increasing amounts of additives on one side, improving processability. Bending stress results obtained with OUA clay showed no significant differences for the various additives used on the other side. The results obtained with OUA clay are desirable since residues processed on each day at the respective factory represent a mixture of different marbles and granites with varying (unknown) compositions. This difference in composition has apparently no additional effect on the bending stress of fired samples of OUA clay masses.