Common Parapet Damages and How to Fix Them

Parapet walls are crucial for buildings’ structural integrity and visual appeal, especially at the roof level. These short walls or railings, often found at the edge of rooftops, terraces, and balconies, serve as a safety barrier and provide weather protection. However, being highly exposed to harsh weather conditions, parapets are prone to various forms of damage over time. Identifying these issues is critical to prevent further deterioration, which could impact the entire building.

This article explores some of the most common parapet damages and effective repair techniques, ensuring your building stays structurally sound and aesthetically pleasing.

Cracked Parapet Walls

One of the most common issues with parapets is cracking. Parapet walls experience frequent temperature changes, which lead to thermal expansion and contraction. This cycle stresses the bricks or concrete and the mortar, leading to cracks that can worsen if not addressed.

Causes

• Weather exposure: Constant shifts in temperature lead to expansion and contraction, stressing the parapet.
• Moisture: Water infiltration can exacerbate cracking, especially in cold weather where water freezes and expands inside cracks.
• Foundation movement: Shifts in the building foundation can create additional pressure on parapet walls, leading to cracks.

Fix

• Repointing: For more minor cracks, repairing the mortar by repointing is an effective method. This involves removing and replacing old, cracked mortar with new mortar to prevent water from entering the cracks.
• Brick replacement: If the cracks are severe, you may need to replace damaged bricks or stones, ensuring the new pieces are adequately sealed and bonded.

Water Infiltration

Since parapet walls sit at the top of buildings, they are heavily exposed to rain, snow, and standing water. Water infiltration is one of the most damaging problems because it can lead to further issues such as internal wall dampness, mould, and even structural weakening.

Causes

• Poor waterproofing: If the parapet is not appropriately sealed during installation, it becomes vulnerable to moisture.
• Coping damage: Cracks or deterioration in the coping stones—the caps on top of parapet walls—allow water to seep in.
• Flashing issues: Inefficient or deteriorating flashing (the material installed to direct water away from critical areas) can lead to water intrusion.

Fix

• Flashing repair: Fixing or replacing the flashing at joints and around the parapet can help redirect water away from vulnerable areas.
• Waterproofing: Applying a water-repellent sealant or membrane is essential for ensuring that water does not penetrate the parapet.
• Coping stone replacement: If the coping stones are cracked or missing, replace them and ensure they are adequately sealed to prevent future infiltration.

Spalling (Surface Deterioration)

Spalling occurs when the outer layer of bricks or concrete starts to flake or chip away. This is usually the result of moisture infiltration, where water penetrates the surface of the bricks, freezes, and then expands, causing the material to deteriorate.

Causes

• Freeze-thaw cycles: Water gets absorbed by the parapet, freezes, and expands, pushing pieces of the material outward.
• Low-quality materials: Inferior quality bricks or improper installation often lead to premature spalling.
• Prolonged moisture exposure: Constant water contact weakens the surface of the bricks, making them prone to damage.

Fix

• Brick replacement: Remove and replace any damaged bricks or concrete blocks affected by spalling.
• Preventive sealing: After replacing damaged materials, apply a high-quality sealant to prevent moisture from seeping into the new materials.

Efflorescence (White Powder on the Surface)

Efflorescence refers to the white, powdery substance that appears on the surface of bricks or stones. This is caused by water that travels through the wall, dissolving salts and minerals, which then crystallize on the surface as the water evaporates.

Causes

• Moisture movement: Water entering the parapet wall and then evaporating leaves behind the salts.
• Poor drainage: Water pooling on top of the parapet due to poor drainage can result in efflorescence.

Fix

• Cleaning: Efflorescence can be removed using a stiff brush or a mild acid wash.
• Waterproofing: Prevent future occurrences by addressing moisture issues, including improving drainage and sealing the parapet to block water absorption.

Bowing and Leaning Walls

A parapet wall that starts to bow or lean signifies significant structural issues. This can be due to moisture weakening the structure or the wall losing its ties to the rest of the building, which provides stability.

Causes

• Water damage: Prolonged water exposure can erode the mortar or corrode metal supports, causing the wall to bow.
• Structural movement: Shifts in the building foundation can push the parapet wall out of alignment.
• Insufficient anchoring: With proper reinforcement ties or wall anchors, the parapet may maintain its stability.

Fix

• Wall ties or anchors: In mild cases, reinforcing the parapet with metal ties or wall anchors can correct bowing.
• Rebuilding: For severe cases, the parapet wall may need to be partially or fully rebuilt to restore stability.

Loose or Missing Coping Stones

Coping stones are the topmost protective layer of the parapet wall, designed to shed water away from the wall. If these stones become loose, cracked, or missing, the parapet becomes vulnerable to water damage and other structural issues.

Causes

• Weather exposure: Over time, coping stones can shift or deteriorate due to weathering.
• Improper installation: Coping stones not installed securely may become loose over time.

Fix

• Reinstall or replace coping stones: Ensure the new ones are correctly sealed and bonded to prevent future water penetration.
• Waterproofing: Applying a sealant on the coping stones can enhance their durability and protect the wall.

Vegetation Growth

In some cases, moss, algae, or even small plants can start to grow on parapet walls, especially if moisture and organic debris are present. While this may seem minor, vegetation can cause severe damage over time by widening cracks and creating further openings for water.

Causes

• Moisture and debris: Moist, debris-filled cracks provide the perfect environment for plants and moss to grow.
• Lack of maintenance: Parapets not regularly cleaned are more susceptible to vegetation growth.

Fix

• Clean and remove vegetation: Remove vegetation using a brush or a mild cleaning solution, ensuring no roots remain in cracks.
• Seal cracks: After removing the vegetation, seal any cracks to prevent future growth and further damage.

Conclusion

Parapet walls, while essential for safety and aesthetics, are highly susceptible to damage from the elements. From cracking and spalling to water infiltration and vegetation growth, timely repairs and regular maintenance are critical to preserving the integrity of parapet walls. Addressing these issues promptly will prevent more extensive, more costly repairs in the future and ensure the long-term health of the building.

FAQs

Q: What causes parapet walls to crack?

A: Parapet wall cracks are often caused by thermal expansion, moisture infiltration, and building settlement over time, which stresses the structure.

Q: How can I prevent water infiltration in parapet walls?

A: To prevent water infiltration, ensure proper flashing, install or repair coping stones, and apply a waterproof sealant to the parapet.

Q: What is spalling, and how can I fix it?

A: Spalling occurs when the surface of bricks or stones flakes off due to moisture. It can be fixed by replacing damaged bricks and applying a waterproof sealant.

Q: Why does efflorescence form on parapet walls?

A: Efflorescence forms when water moves through the wall, bringing salts to the surface crystallizing as the water evaporates. Improved drainage and waterproofing can help prevent it.

Q: How do I address bulging in my parapet wall?

A: Bulging walls can be reinforced with wall ties or anchors, but in severe cases, the wall may need to be rebuilt to restore structural stability.