What Is Dead Brick in a Chimney?

Chimney Information

• The chimneys on many older homes often were not lined, exposing the bricks to direct contact with stove or fireplace emissions and the intense heat generated by a wood fire. Time also took its toll on these old chimneys, as the bricks absorbed moisture and the constant heating and cooling effect destroyed the mortar between them. Bricks also undergo a process called spalling, which is the gradual chipping away of their exterior surfaces. If constantly exposed to rain, they become saturated, and once dry, develop cracks and chips making them incapable of sustaining the weight of the surrounding bricks and mortar.

Brick Facts

• While bricks normally last for many years, external conditions often shorten that time until they are no longer carrying their share of the load in a chimney. Dead brick crumbles easily and no longer adheres to the mortar, creating large gaps in the chimney that make it unsafe to use. Dead brick loosens and pulls away from the surrounding mortar and often falls out in high winds or driving rain. Missing bricks leave gaps that allow more rain and snow in and that can interfere with the transfer of smoke from a wood fire. Crumbling brick and mortar can also fall into the bottom of the chimney where they accumulate and may eventually block the flue opening leading from the fireplace or the wood stove.

Repairs or Replacement

• In cases where the damage is not too severe, repointing can be done to save the chimney. This involves removing the dead brick and as much of the old crumbling mortar as possible from the opening, replacing it with new brick and applying new mortar on all sides to reattach it to the existing brick. Repointing is successful if the surrounding chimney materials are still relatively sound, but more severely damaged chimneys may need to be completely rebuilt.

Considerations

• Chimneys also provide shelter for birds, bats and other creatures who build their nests there. Debris from overhanging trees, including wind-blown seeds, can also clog a chimney, with some plants actually taking root in old dead bricks, creating cracks in them as they expand. This necessitates removing the old bricks and replacing them with new ones, as well as trimming the nearby trees that caused the problem. Gaps in chimneys caused by crumbling brick can release toxic gases into a building and allow sparks to escape, creating a serious fire hazard. Loose bricks can also fall out of a chimney, causing property damage or personal injury.