Even as all tiles will eventually become vulnerable to damage over the passage of time, the
rate of failure for clay tiles depends on a number of reasons:
- The temperature that they were fired in the kiln. By using tiles that were in a cooler part of the kiln or were exposed to air before the process had ended, will mean that the clay will not be fully vitrified, leaving large air gaps between the shaled surfaces which, when exposed to freeze/thaw action, are brittle and cause the surface of the clay tile to delaminate.
- The roof exposure. For instance, we noted that delamination had occurred to significantly higher levels on the north elevation of the roof.
- The pitch of the roof. Steeply pitched roofing being less susceptible.
- Detritus and surface contaminants will also have an effect on the rate of failure of clay tiles - a roof that cannot shed water rapidly may retain moisture which results in water penetrating the inner skin of the tiles which in turn allows frost action to occur.