The Deterioration of Terracotta  and Faience

"In common with all building materials, if not properly maintained, terracotta and faience will deteriorate over time. This deterioration can take a number of forms and be caused by various factors. The main indicators of deterioration are as follows:
• Glaze crazing or spalling
• Material spalling
• Cracking
• Rust staining from failed anchoring systems

The main cause of such deterioration is water ingress. This can be caused by cracks in the material allowing water to penetrate, excessive wear caused by water run-off from defective rainwater goods or the inappropriate attachment of fixings rupturing the surface fireskin or glaze. One of the worst causes of this type of damage, however, is inappropriate cleaning."