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Causes of Chimney Crown Cracks

The cement or stone crown at the top of your chimney plays a crucial role in preserving the health of your fireplace’s ventilation system.  Bricks and mortar tend to act like a sponge, naturally absorbing moisture.  Unlike a sponge, when the moisture in masonry freezes and thaws, it breaks down.  This freeze and thaw cycle can weaken the structural integrity of your chimney and cause thousands of dollars in damage.  Protecting the health of your chimney crown can extend the life of your chimney and prevent the need for expensive repairs.

A chimney crown is a cap at the top of your chimney that covers the bricks and mortar or stones that make up the structure of the chimney.  Its purpose is to prevent moisture from seeping into the chimney’s masonry where it is most exposed to the elements: at the top.  It also extends over the edge of the chimney by a few inches so that rain and snow will run off onto the roof or the ground instead of falling straight down to the base of the chimney which would cause extra wear and tear to the flashing.

Chimney crowns are usually made of concrete that has been covered by a waterproofing sealant.  Though they can also be made of metal or stone.   A properly designed chimney crown will have a minimum slope of 3 inches per foot of run and will extend over the side of the chimney by a minimum of 2 ½ inches.

Below are several reasons why chimney crowns may crack:

Natural wear and tear

Overtime, the waterproofing sealant on the chimney cap will become less effective.  If the crown is not retreated with sealant, water can seep into the concrete.  When it freezes and thaws inside the concrete, it can begin to crack creating pathways for moisture to seep into the masonry.

Improper construction

If the chimney crown doesn’t have a steep enough slope or isn’t made of the correct materials, it is more likely to crack or break.

Shifting and settling

Homes shift and settle as the foundation sets and ground shifts.  The chimney crown can become cracked during this process.

Concrete shrinkage

As the moisture content in concrete evaporates, as it dries and ages, it can cause concrete shrinkage. Sever concrete shrinkage can cause the crown to crack.

Freeze-Thaw Cycles

Freeze-thaw cycles are yearly events caused by weather action.  Chimneys are largely exposed to such severe weather conditions.  What results is a situation where moisture soaked into small cracks freeze due to extremely low temperatures.  This is later followed by a thawing process.  The continued freeze-thaw cycles take their place on a chimney as creates cracks and widen existing ones.  This will have to be fixed by having all cracks sealed.

Lack of Maintenance

Lack of maintenance will normally affect the basic functioning of a chimney structure.  Lack of maintenance refers to taking no action at all to inspect and fix a chimney.  With such a situation, it’s only normal that steady deterioration begins to unfold.

Soils with Poor Load Bearing Capacity

Certain soils are known to have the poor load-bearing capacity.  When such is the case, the chimney’s foundation or footing becomes unstable.  This condition takes its toll on the chimney with cracks appearing along with the masonry.

Poor Drainage

Poor drainage could be the reason why a chimney cracks.  This is common for pooling water found around a chimney footing.  When there’s no slope slanting away from the chimney, water pooling becomes inevitable.  This situation results in settling or expansion, thus causing instability in the structure, with cracks resulting.

Damage Due to Heat

Thermal damage is one of the possible reasons why your chimney is cracked.  When basic a component such as a liner is damaged or absent, the bricks are exposed to excessive heat from a fireplace.

Tree Damage

Do you have trees having large root systems around your compound?  If you do, these could be the reason why you’re seeing cracks on your chimney.  As these roots spread out, they may cause damage to your chimney foundation.

Mechanical Damage

This is mostly the case when high or sizeable antennas are hoisted up on chimneys for better reception.  These will add weight to the chimney structure, thus causing pressures that may result in cracks.  Harsh weather actions like wind storms will accelerate this process.

Risks Posed By Chimney Cracks

Whether you’re looking at cracked chimney masonry or cracked chimney flue, several risks are posed by such conditions. Any form of break creates a problem.  For cracked chimney masonry, these are likely to further disintegrate due to weathering action.  Chimney cracks can deteriorate to the extent where the entire structure crumbles or topples over.  This poses a significant risk to injury among other things. For chimneys, cracks may extend to the flue components.  With such action, there’s little protection from toxic gases.  There’s also a high likelihood of corrosion occurring. This steadily erodes your chimney structure when left unattended.