A chimney is constructed with layers of brick with mortar in between the bricks. This keeps the chimney intact. Over the years, due to exposure to the elements (especially in the north where it moves between cold in the winter and warm in the summer), the mortar joints will decay and create voids between the bricks.
If your chimney’s brick are in good shape but the mortar joints are loose, repointing is the likely path forward. Repointing will repair the appearance and the structure of the chimney, and most importantly, prevents further damage and moisture from entering between the bricks as you can see in the following image.
Repointing involves grinding out the mortar joints between the brick by ½”. The joints are then filled back in with new mortar and the excess is removed.
Here is another chimney that was repointed and the flashing replaced.
After repointing, it is recommended that the chimney be waterproofed.