Spalling vent tile

[Michael Thomas]

For future reference, what would cause this sort of spalling? NW corner, the interior was in good condition. Manufacturing defect?

[Scott Patterson]

For future reference, what would cause this sort of spalling? NW corner, the interior was in good condition. Manufacturing defect?

Moisture getting into the terracotta. Could be from several factors. A common one I have seen is under fired clay. They simply do not get the tiles hot enough when they are fired. Age can also be a factor.