How Water Moves Through Brick And Stone Walls On Your Historic Masonry Home
How Water Moves Through Brick and Stone Walls on Your Historic Masonry Home
Understanding how water travels through brick and stone is essential to preserving your historic masonry home. Unlike modern construction systems engineered to completely repel water, traditional masonry assemblies are designed to manage moisture, not eliminate it. Brick, stone, and historic mortar are breathable materials that absorb and release moisture naturally.
When this balance is maintained, your historic masonry home performs remarkably well for generations.
Masonry Is Meant to Breathe
Brick, stone, and historic mortar are all porous materials. This means they contain microscopic pores that allow water vapor and small amounts of liquid water to pass through.
Water enters masonry walls through:
Wind-driven rain
Capillary action (water drawn upward from the ground)
Vapor diffusion
Small cracks or open joints
In a properly functioning wall, moisture is temporarily absorbed and then released as the wall dries. This process is often referred to as vapor permeability, or “breathability.”
Historic mortar plays a critical role in this system. It is intentionally softer and more permeable than the surrounding brick or stone. This allows moisture to move through the mortar joints rather than the masonry units themselves.
The Role of Capillary Action
Capillary action is one of the most important forces affecting your historic masonry home. Masonry materials behave like a sponge. When water is present at the base of a wall, it can travel upward through tiny pores in brick, stone, and historic mortar.
This upward movement explains:
Rising damp near foundations
Efflorescence (white salt deposits)
Interior plaster deterioration at the lower wall sections
The finer the pore structure, the higher the water can travel. Managing drainage and limiting prolonged water exposure at the foundation is critical to reducing this effect.
How Evaporation Protects the Wall
The survival of your historic masonry home depends on evaporation. When moisture enters the wall, it must also be able to leave.
Historic mortar allows:
Moisture migrates outward
Salts move toward the surface
Controlled drying without trapping water inside
If drying occurs evenly, masonry remains stable. Problems arise when evaporation is blocked.
What Happens When Moisture Gets Trapped
Using incompatible mortar during repointing is one of the most common causes of trapped moisture. Incompatible mortar is often harder and less permeable than traditional historic mortar.
When moisture cannot escape through mortar joints, it is forced through brick or stone instead. This can lead to:
Surface scaling or spalling
Cracking during freeze-thaw cycles
Salt damage beneath the surface
Long-term material breakdown requiring reconstruction
In freeze-thaw climates, trapped moisture expands as it freezes. This expansion places internal pressure on masonry units, accelerating deterioration.
Wind-Driven Rain and Wall Saturation
Wind-driven rain can push moisture deep into brick and stone walls. Thicker masonry walls, common in your historic masonry home, often absorb substantial moisture during storms.
However, these walls were designed with drying capacity in mind. When gutters function properly, and repointing is performed with appropriate historic mortar, walls can dry naturally after rainfall.
Persistent saturation typically indicates:
Failed historic mortar joints
Poor drainage
Incompatible mortar repairs
Sealed surfaces that block evaporation
The Importance of Compatible Materials
Historic masonry systems rely on balance. Brick or stone units are durable, while historic mortar acts as the sacrificial element. When repointing is needed, matching permeability, strength, and composition is essential.
Proper restoration tools and traditional techniques help preserve the wall’s moisture management capacity. Altering this balance with incompatible mortar can shift stress into the masonry itself.
The long-term Character, durability, and appearance of your historic masonry home depend on allowing materials to function as originally intended.
Conclusion: Understanding Moisture Preservation
Water movement through brick and stone is not a defect—it is a design feature of traditional masonry construction. Your historic masonry home was built to absorb, channel, and release moisture in a controlled way.
When historic mortar remains breathable and compatible, masonry walls can endure for centuries. When moisture pathways are blocked or altered, deterioration accelerates.
A clear understanding of how water moves through masonry allows informed decisions that protect the longevity and stability of your historic masonry home.
