There are many reasons why a chimney may develop a leak. Although some reasons are due to roofing issues, there are quite a few that are caused by issues with the brick masonry. A masonry contractor can fix these issues.

1. Brick Damage

Cracks and chips in the bricks themselves can lead to a chimney leak. Moisture seeps into this small damage. In freezing weather, the moisture can freeze and expand, which then makes the cracks larger. This allows in even more water. A brick mason will either patch or replace the damaged bricks, depending on the extent of the damage and the visibility of the repaired area.

2. Failing Mortar

The mortar is what holds the bricks together. Mortar often doesn't last as long as the bricks themselves, because it is more prone to crumbling and wear. Cracked and crumbling mortar can allow water to leak through. A mason can tuckpoint the mortar. In this process the old mortar is scraped out from between the bricks and new mortar is put in. The bricks themselves are never removed. 

3. Damaged Crown

On top of a brick chimney is the crown. This is a thick layer of mortar and sealants that is installed on top of the last course of bricks that make up the chimney. Over time, the crown can weather until it develops chips and cracks. Impacts, such as from hail or objects blown by the wind, can speed the process. Fortunately, a mason can rebuild the crown and seal it well so that future leaks won't be a problem. 

4. Missing Cap

On top of the crown is the chimney cap, which is often made of cement brick combined with screening to keep out birds and debris. Caps can be knocked askew by the weather or small animals, or they can crack and crumble due to aging. Depending on the issue and the damage, a mason can re-seat your existing chimney cap or install a new one. Damaged chimney caps often occur in conjunction with damage to the crown.

5. Failing Masonry

Older brick chimneys may suffer total failure. Often, a chimney on an older home is not seated directly on the house foundation. This means it may begin to tilt or skew to one side as the ground beneath it sinks and settles. Age can also simply cause the bricks to lose their strength until they begin to give out and crumble. In this case, it is best to remove the old chimney and have your mason build a new one. 

Contact a brick masonry contractor if you notice a leak in the chimney or damage to the bricks.