Often a careless mason will not adequately "butter-up" the ends of the bricks during installation, resulting in deterioration of the joint. Overtime, if open cavities are not fixed properly, it can lead to a bigger problem. Cracks spalled or loose masonry, and missing mortar can cause venting issues and weaken the structure of the masonry walls. missing mortal and cracks in between the bricks can allow water intrusion into the wall and cause potential leaks inside the home and damage wall structural. Repair and maintenance of your masonry walls is crucial to its safety and functionality. When heat, moisture and gases escape though gaps and cracks in your chimney, they can deteriorate your chimney from inside ou. More importantly, the gaps and cracks can cause health risks, by allowing poisonous gases to escape into you home.