Replacing damaged brick can be a less expensive repair for your chimney than rebuilding the entire structure. Where a full rebuild is warranted, cutting out and replacing brick is not an acceptable alternative. However, when appropriate, repairing only parts of the chimney can be the most economically sound decision for you as a homeowner.
Bricks that are severely damaged will be cut out using masonry tools, leaving perfect, brick sized holes in the chimney. Diamond blade saws or regular chipping hammers are used to remove the bricks, although the saw is least likely to chip the brick that you do want to keep intact.
The openings must be cleaned properly before new installation can occur. Using fresh pointing mortar, a mason will install new brick into these openings. There are some downfalls to this method however. 99% of the time, there will be a color difference between the new bricks and the old bricks. Often times, the mortar may not match completely either. These minor details are not significant when it comes to a very small brick wall repair on inconspicuous parts of the home, but a very widespread repair on the front of the house or on the top of the chimney can be very unsightly if some bricks are a different color than the others. Mortar may sometimes get on the face of the brick as well, and although it can be removed, can be a real pain and eyesore if not removed shortly after the brick repair has been completed.
The most important step after conducting repairs of this nature is to waterproof not only the repaired area but all the surrounding brick. Because these used brick are weak, they are more prone than new brick to spall, crack, and crumble. A heavy duty water repellent is my greatest recommendation to prolong and protect the repair.