As odd as it may seem, water causes more damage to masonry chimneys than fire.
Water penetration can cause interior and exterior damage to your home and masonry chimney including:
- Spalled and broken brickwork
- Deteriorated metal or masonry firebox assemblies
- Rusted damper assemblies
- Rotted adjacent wood and ruined wall coverings
- Deteriorated central heating system
- Decayed mortar
- Cracked flue liner systems

PREVENTING WATER DAMAGE
Following are the four main ways to prevent water damage.
2.) Repair or replace a damaged chimney crown.
3.) Repair or replace flashing

IN CONCLUSION:
Water damage to masonry chimneys is usually a slow, subtle process. The problem is often not evident until it has become quite serious.