Masonry structures, known for their durability and aesthetic appeal, can be vulnerable to water penetration, leading to structural damage and reduced performance over time. Effective water resistance in masonry depends on several factors, including materials used, wall type, and the quality of workmanship. This article explores comprehensive methods to improve masonry resistance against water penetration, categorized into design and construction techniques.
Methods to Enhance Masonry Water Resistance
1. Methods Related to Design and Specifications
The design and specifications of masonry walls play a critical role in their water penetration resistance. Thoughtful design considerations can significantly improve masonry performance under various environmental conditions.
a. Wall Type Selection
Selecting the appropriate wall type is essential for addressing the anticipated severity of rain in the project location. For areas prone to heavy, wind-driven rain, the use of completely grouted barrier walls or drainage walls with a minimum thickness of 20 mm is recommended. These walls act as robust barriers, preventing moisture infiltration.
b. Design of Drainage Walls
Drainage walls are designed to prevent water penetration through the outer Wythe of the masonry wall. Key considerations include:
- Crack Prevention: Preventing cracks under service loads is crucial. For masonry cement, which has lower tensile bond strength, ensure that veneers are designed to avoid cracking. When steel studs are used, their flexibility should be accounted for to minimize cracking risk.
- Sealant Specification: Proper sealants must be applied to outer Wythe joints to block rainwater infiltration effectively.
c. Cavity Wall Design
Cavity walls provide an additional defense by incorporating a drainage mechanism. The following considerations are essential for effective cavity wall design:
- Open and Drained Cavity: Ensure the cavity is kept open and drained using appropriate flashing and weep holes.
- Cavity Maintenance: Use tools like boards to clean debris and maintain a minimum cavity width of 50 mm.
- Vapor Barrier Placement: Position vapor barriers on the exterior face of the interior Wythe to prevent interstitial condensation.
- Durable Wall Ties: Use stainless steel or hot-dip galvanized ties to resist corrosion and maintain structural integrity.
d. Accommodating Differential Movements
Differential movements within masonry walls, caused by material expansion, contraction, or structural loads, can lead to cracks. Key design considerations include:
Horizontal Expansion Joints:
- Essential for clay masonry walls that expand due to moisture and freeze-thaw cycles.
- Place these joints under shelf angles with a minimum gap of 3.65 mm, accounting for sealant shrinkage over time.
Vertical Expansion Joints:
- Install at wall corners to prevent cracking due to expansion forces.
Breaking Concrete-Masonry Bonds:
- Avoid bonding clay masonry to concrete slabs, roofs, or foundations to prevent cracks caused by differential strains.
Control Joints at Openings:
- Place control joints around windows and doors to accommodate shrinkage stresses.
Brick and Block Walls:
- Analyze the effects of restricted differential movement on wall deformation and incorporate appropriate measures.
2. Methods Related to Masonry Construction
Even with excellent design, poor construction practices can compromise masonry’s water resistance. Adhering to high standards in construction methods ensures durable and water-resistant masonry structures.
a. Mortar and Masonry Compatibility
The compatibility of mortar and masonry units is crucial. Guidelines include:
- Proper Mortar Mix Design:
- Follow ASTM C780 blending procedures to ensure proper bonding and workability.
- Begin by mixing cementitious materials with sand and water to achieve a consistent mixture.
- Timely Application:
- Install masonry units immediately after spreading mortar, avoiding delays or excessive tapping that can weaken the bond.
b. Joint Practices
Joints in masonry walls must be constructed to maximize water resistance:
- Full Head and Bed Joints:
- Ensure joints are fully filled to prevent water seepage.
- Raked Joints:
- Recommended for interior masonry to enhance aesthetic appeal while maintaining functionality.
c. Maintaining Mortar Workability
Mortar workability is essential for strong bonds. Key practices include:
- Retempering Mortar:
- Maintain proper workability by retempering as needed during construction.
- Time Management:
- Discard mortar if not used within two hours of initial mixing to ensure optimal performance.
d. Surface Preparation and Curing
Proper preparation and curing processes ensure durable masonry:
- Foundation Cleaning:
- Thoroughly clean the foundation before laying the first layer of masonry.
- Dampening Walls:
- Lightly dampen masonry units to facilitate mortar curing and enhance bond strength.
Conclusion
Improving the water penetration resistance of masonry structures requires a holistic approach that integrates meticulous design and high-quality construction practices. By selecting appropriate wall types, accommodating differential movements, and employing compatible materials with proper workmanship, masonry structures can achieve exceptional durability and resistance to water-related damage. These methods not only extend the lifespan of masonry but also enhance its overall performance and sustainability in the face of environmental challenges.