Made from a mixture of clay, particles of previously fired clay, and additives, terra cotta units are formed by molding or extrusion, coated with a glaze or a slip coat of water and clay, then allowed to dry for up to several months before firing. Properly manufactured and well-maintained, terra cotta can have a long service life. Unfortunately, inadequate maintenance and improper detailing of terra cotta facades hastened the deterioration of this rich material on some building facades. CAUSES OF DETERIORATION Terra cotta, like other masonry materials, may deteriorate from water. Water that penetrates the wall causes corrosion of the metal anchorage system that typically ties terra cotta cladding back to the structure. Structural and thermal movement also must be accommodated in the design of terra cotta facades, belt courses, and copings. INVESTIGATIVE TECHNIQUES Any effective terra cotta restoration project requires an investigation to learn just how the material was used and determine appropriate repairs. Walk through the building to identify typical distress and areas of special concern. When intrusive techniques are necessary, careful planning can limit their destructiveness. REPAIR TECHNIQUES Nonmoving cracks that extend into the body of the terra cotta may be pointed with mortar; moving cracks should be caulked with sealant. Large, deep spalls in terra cotta can be patched with a mixture of portland cement, lime, sand, and an acrylic bonding agent. REPLACING DAMAGED TERRA COTTA When replacement with new terra cotta is not feasible, the following substitute materials have been used: glass-fiber- reinforced concrete; precast concrete; cast stone; fiber-reinforced polymers; cast metals; sheet metals. If properly restored and maintained, terra cotta buildings will survive for the enjoyment and service of future generations.