Brick and mortar chimneys are a common site on rooftops of a certain age in Washington State. A common point of deferred maintenance and long term damage is at the chimney cap. This is the mortar cap at the top of the chimney that protects the top of the chimney and bricks below. 

Water tends to pool and collect on the top of the chimney cap. This can lead to moss growth and erosion of the mortar which over the long term leads to cracks and cap failure. Eventually the cap will split and be in danger of falling off the chimney on to the roof or to the ground below. ​

If a chimney cap is at the point of damage like in these pictures, it needs to be repaired or replaced. Preventative maintenance is the regular cleaning of moss and the installation of a rain cap over the flue that extends over the edges of the chimney. 

Brick and mortar chimneys exposed to water over time will deteriorate. Though bricks are more or less indestructible the mortar holding them together is prone to damage and eventual failure. Once the mortar between the bricks cracks and begins to fall out the bricks and structural integrity of the chimney are sure to follow. 

These pictures show some typical long term water damage to the mortar between bricks on a above roof chimney. Someone noticed this problem before and attempted to fix the failing mortar with silicone caulking. This is not the correct repair technique - caulking is not going to do anything to stabilize the brick.

This chimney needs repair - the bricks need to be "re-pointed". Re-pointing is the process of removing the old mortar joints and replacing with fresh mortar. This is within the realm of ability of most homeowners but it is a tedious job and depending on location could pose some safety concerns. If this project doesn't appeal to you or you are not comfortable being on your roof, look for a masonry repair specialist to do the job.

The following is a link to a nice overview of repointing-brick on the This Old House website. 

Have you ever noticed a white chalk like deposit on a brick wall or chimney? This is efflorescence - a salt deposit on the surface of masonry associated with water moving through the wall. This is usually just a cosmetic problem and can be cleaned off by light scraping. However, efflorescence can serve as a clue to an underlying moisture or water penetration problem in the surrounding structure.

The efflorescence deposits in this picture are on a chimney side just under the penetration through the roof. It is very likely that the flashing and water sealing of the chimney/roof joint are failing. This homeowner needs to take a closer look at the roof structure and shingles to see if there is further hidden damage that needs repair.

A recurring theme - water causes problems if it gets to places it is not supposed to be in.

This chimney is a bit weathered and has no protection from the rain. Exposure to water over the years has deteriorated the mortar between the bricks. It's now at the point where the bricks are loose and have the potential to tumble off the roof. Not good if you happen to be standing in the back yard.

This is a non working and abandoned chimney, when the roof is replaced it would be a good idea to remove the chimney to below the sheathing and roof over the opening.

In the meantime, the chimney needs a rain guard / rain cap to be installed once the loose bricks are removed and a stable base is established. This will reduce the chances of water intrusion and help preserve the remaining mortar. No more bricks falling off the roof.
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