Introduction of ceramic sludges lone to seven percent by weight) from the glazing lines of ceramic floor and wall tile factories to calcareous clays (the most common raw material for the manufacture of brick) was found to reduce drastically and even eliminate the formation of efflorescent salts. At low sludge additions (one to two and a half percent by weight), the formation of soluble alkali sulfates (Na₂SO₄ and K₂SO₄) was inhibited in favor of double sulfates such as K₂Na(SO₄)₂ and K₂Ca(SO₄)₂ . H₂O. At higher sludge contents, the formation of all soluble sulfates was drastically reduced, possibly as the result of the reaction between lead contained in the sludge and SO₃ released by the clay during firing, with the consequent formation of insoluble lead sulfate. Nevertheless, certain boundary conditions must be met to achieve useful applications of the process. -- AATA