Masonry Clay Flue Tile Defects
Masonry clay flue tiles meet a harsh environment inside the chimney. Corrosive condensation, moisture, chimney fires, and other conditions may damage a flue tile. In certain circumstances, a clay flue tile can last for decades, provided they are maintained and the homeowner operates the appliance or burns responsibly.

Latent Defects are defects found within the system from improper and sometimes creative use of material that stray from building codes or the manufacturer's installation instructions. This deviation from the codes or installation instructions creates various issues within an installation.

Wear and Tear is the natural aging process where material breaks down over time. Wear and tear can also include how an appliance is operated. If it is too hot, it decreases the life of the appliance, chimney, and connector pipe. If the temperatures are too low, it can create a tar-like creosote and increase the likelihood of a Sudden Occurrence (or condensation with gas/oil). Another factor is maintenance or lack of maintenance. Wear and tear can sometimes overlap with other categories.

Moisture and Condensation damage occur when water enters the chimney interior due to a missing cap, leaking crown, cracks in the brick structure, freeze-thaw breaks in the bed or head joints, and a poor choice of brick, causing excess water absorption. Another source of water in a chimney can come from condensation. This condensation occurs when the flue gas temperature falls below the dew point. Because of the water percentage in natural gas and liquid propane, the flue gases may condense in masonry chimneys, especially those located along the home's exterior.
The next fuel to condense is wood. When the warm gases reach the masonry flue liners, they, too, cool off. The moisture is included with the other byproducts of wood burning – black creosote, watery or tarlike soot.
The last fuel, oil, will also condense on the masonry walls. Due to the higher efficiencies that oil appliances can now operate, they too will condense and, with their acidic nature, can destroy masonry clay flue tiles.

A Sudden Occurrence is a sudden event that causes damage. It can be a chimney fire, a sudden weather-related incident(s) such as a tornado, strong wind, or a seismic event. It has to be out of the ordinary of daily operations.
A Sudden Occurrence, the last Pathway, includes damage seen from a direct and sudden event. Indirect manners can apply to areas where mine subsidence has occurred (where mining was performed). Of the Pathways, this last defect(s) will usually become an insurable loss. The other three defect categories – Latent Defect, Wear & Tear, and Moisture are generally not insurable losses since insurance contracts (policies) do not include them.