Why are the Bricks on My Chimney Starting to Crumble?

Are you concerned that parts of your chimney look like they are crumbling? This is a common problem for homeowners with a fireplace. In most cases, cracked bricks and crumbling mortar are a sign of spalling.

Spalling is a problem for brick structures like retaining walls and chimneys. It is a symptom of water damage that has begun to deteriorate the masonry. Learning how to reduce the effects of spalling can save you from expensive future repairs.

What Causes Spalling?

Moisture is the biggest threat to masonry. Since bricks and mortar are porous, they can absorb water like a sponge. Unlike a sponge, when this water freezes and thaws it breaks down the masonry causing cracks and breaks. The cycle of freezing and thawing can dramatically deteriorate the integrity of masonry structures over time. This is what causes spalling.

Most spalling occurs where there are easy pathways for water to enter masonry like where the bricks meet windows, gutters or the roof. Chimneys that do not have a chimney cap or chase cover to prevent rainwater or snow from falling down the flue are more vulnerable as well. The risk of spalling also increases if:

• Your home or chimney was made with salvaged bricks.
• You live in a colder climate where it reaches freezing temperatures.
• You use a pressure washer or sandblaster to clean the bricks’ surface.

How Can Spalling Be Fixed?

The solution for addressing spalling will depend on how water is getting in and how severe the spalling is. Identifying how moisture is getting into the chimney is a crucial part of the solution because, if you only treat the symptom, spalling will continue to grow and spread. If a chimney technician recommends a solution for spalling without identify how water is getting into the chimney, you should consult another one.

For minor damage, treating the masonry with vapor-permeable waterproofing sealant or installing a chimney cap may be all that you need to do. Vapor-permeable waterproofing allows condensation from the fire to escape from the masonry but doesn’t allow it to absorb outside moisture. A chimney cap or chase cover will prevent rainwater and snow from falling down the chimney.

The solution may be more complex and expensive if the damage is more serious or if there are structural problems causing water to collect in the chimney. It may be that the chimney needs a new crown or a new liner because it was fitted with a liner that is the wrong size. Sections of the masonry may need to be rebuilt to restore the structural integrity of the chimney if there is severe damage.

The only way to know the best solution for your chimney is to have it appraised by a certified chimney technician. A qualified chimney technician will show you video or photographic evidence of the extent of the damage and will recommend the best solution.

Masonry deterioration is serious. A chimney can collapse when the bricks and mortar have been severely weakened. If you notice signs of spalling, contact a qualified chimney specialist!