There are many reasons why a new chimney can develop cracks. For instance if your new chimney was built using mortar chimney caps these can sometimes be very vulnerable to cracking at the joints as the mortar shrinks.

Also exposure to the natural elements such as wind, sun and snow, as well as a recent earthquake, may also be the cause of your new chimney developing cracks.

If you have developed minor cracks in your new chimney especially around the joints between the flue and the cap these can be repaired easily enough with a little masonry caulking compound.

If you discover that the caps are crumbling you will have to chip out the old, mortar and apply a new layer of ready-mixed mortar with a trowel, then keep the mortar damp for at least four days until it is properly cured.

It is important that you slope the new mortar away from the flue in order to allow the rain water to drain off correctly.