Chimneys are located on the highest part of most buildings where they are buffeted by the elements, particularly, rain snow and ice. 
Chimneys tend to deteriorate due the fact that they get wet and stay wet for long periods of time.
Blowing winds tend to force rain water into small cracks between the bricks or the pointing.
Freezing causes the moisture in the bricks and the mortar to expand, hence the cracks.
Regular maintenance is needed to prevent expensive repairs.
Chimneys need sealant applied more often than the brick work of the building.
On newer brick apply once every 5 to 10 years.
On older brick, where the surface is porous the sealant will have to be applied more frequently, such as every 4 to 7 years.
The waterproofing sealant should be applied to any stucco or concrete finish around the base or top of the the chimney.
Choose a sealant that’s both breathable, penetrating, and water based. 
A good waterproofing sealant will form an invisible barrier protecting the brick against moisture penetration and attacks of airborne pollutants that deteriorate the pointing and the bricks exterior.
Sealant resists dirt accumulation and retards the formation of efflorescence.
Sealant will need to be reapplied when water no longer forms “beads” on the wet surface.
The length of time between coats will depend on the porosity of the brick and weather conditions (prevailing winds, etc.).
Sealants are easily applied with a brush or using a deck or waterproofing hand sprayer.
