RAS Engineering is a professional engineering company serving building managers and owners by providing advice, oversight restoration, and testing to ensure that all components of a build’s exterior and structure meet the standards necessary to provide quality durability and safe protection against the elements.
Hurricane Damage on Portland Cement Plaster (Stucco)
Stucco, known for its aesthetic versatility and durability, has been used for centuries as an exterior cladding material. In modern construction, stucco is also referred to as Portland cement plaster. It is composed of a mixture of Portland cement, lime, sand, and water, often enhanced with various admixtures for improved performance. Despite its robustness, stucco is not impervious to extreme weather conditions, particularly hurricanes. This blog will explore how hurricanes affect stucco, how to assess the damage, and the necessary repair methods to restore its integrity.
What is Portland Cement Plaster (Stucco)?
Portland cement plaster is a durable cladding material made from a blend of:
Portland cement (grey or white)
Lime (optional but common)
Masonry sand
Water
Additives such as air-entraining agents, accelerators, or water repellants are often included to enhance the properties of the plaster. This versatile material is applied to various substrates, typically in two or three coats depending on the system, making it a resilient barrier against the elements when installed correctly.
Stucco is typically applied over two types of substrates:
Direct-applied bases like concrete or masonry.
Metal lath plaster bases attached to substrates like wood or metal framing, which require a weather-resistive barrier (WRB) to protect the underlying material from moisture.
Stucco in Hurricane-Prone Areas
Stucco's hard and dense surface makes it a tougher cladding material compared to alternatives like EIFS (Exterior Insulation and Finish Systems). While it is better equipped to withstand flying debris and high winds during hurricanes, it is still vulnerable to various forms of damage such as cracking, spalling, delamination, and moisture intrusion.
Hurricanes expose stucco-clad buildings to several stress factors, including:
High winds: Pressure from hurricane-force winds can cause stress on the stucco system, potentially leading to cracking or detachment.
Wind-borne debris: Flying debris can puncture or crack stucco, especially at lower elevations.
Water intrusion: Prolonged exposure to wind-driven rain can lead to water penetrating the cladding, especially if there are weaknesses like poor installation, cracks, or failed sealants.
Common Types of Hurricane Damage on Stucco
Stucco may show visible and hidden signs of damage after a hurricane. Some of the common problems include:
Cracking: High winds can cause hairline or larger cracks in the stucco, particularly at weak points like corners, joints, or around windows and doors.
Spalling: Portions of the stucco surface may flake off or "spall" due to moisture penetration or impact from debris.
Delamination: Layers of stucco can become detached from the substrate, causing bulges or hollow sounds when tapped.
Moisture intrusion: Hurricanes bring significant moisture, and if stucco is compromised, water can infiltrate the underlying materials, leading to structural damage or mold growth.
Level 1 Assessment of Stucco Damage
Assessing stucco after a hurricane involves a thorough inspection to identify both visible and concealed damage. A Level 1 Assessment includes data gathering, noninvasive investigation, and invasive testing when necessary.
Preliminary Data Gathering
The first step is to review any available construction documentation and ASTM standards related to stucco application, such as ASTM C926 (for application) and ASTM C1063 (for installation of metal lath bases). These references will provide insight into the building’s specific stucco system and help guide the inspection process.
Noninvasive Investigation
A visual survey is conducted to examine the exterior condition of the stucco. The following aspects are reviewed:
Surface finish: Checking for fading, chalking, or worn spots.
Cracking: Identifying patterns or repetitive cracking that could indicate underlying stress or damage.
Delamination: Looking for bulging or hollow spots indicating the stucco has detached from its substrate.
Penetrations and sealants: Inspecting around windows, doors, and other penetrations to ensure the integrity of building sealants.
Control and expansion joints: Ensuring these joints are in place and functioning properly to prevent cracking due to movement or temperature changes.
For stucco, sounding techniques can be useful to detect areas of delamination. By tapping the surface with a metal hammer or chain, inspectors can differentiate between solidly adhered stucco and sections that may be detaching.
Invasive Investigation
If noninvasive inspection reveals potential issues, an invasive investigation is required. This involves:
Moisture testing: While nonpenetrating moisture meters are ineffective on stucco with metal lath, penetrating moisture probes can be used. Pre-drilling holes into the stucco allows probes to be inserted to detect moisture at the sheathing layer.
Substrate evaluation: Accessing the backside of the stucco from attics, utility areas, or unfinished rooms to check for staining, water damage, or structural deterioration in the framing.
Framing assessment: Inspecting framing members, connections, and anchors to ensure they have not been compromised by water intrusion or wind forces.
Level 2 Assessment of Stucco Damage
If a Level 1 Assessment indicates significant damage, or if the building is in a region with high wind speeds (e.g., over 120 mph), a Level 2 Assessment is recommended. This involves more detailed methods like infrared thermography, selective demolition, and laboratory testing.
Infrared thermography: This non-destructive technique can reveal thermal anomalies indicating moisture trapped within the wall system. However, metal lath can complicate readings, so follow-up tests may be needed to confirm results.
Selective demolition: Small sections of stucco may be removed to directly observe the condition of underlying materials.
Laboratory testing: Samples of stucco can be tested to determine their structural integrity and performance characteristics.
Conclusion
Portland cement stucco is a durable and widely used cladding system, but it is not immune to the destructive forces of hurricanes. High winds, flying debris, and water intrusion can lead to significant damage if not addressed promptly. Regular assessments and repairs are vital to maintaining the integrity of stucco in hurricane-prone areas.
Building professionals and property owners should prioritize thorough post-storm inspections to identify issues early and prevent long-term deterioration. By understanding the vulnerabilities of stucco and implementing proper repair strategies, buildings can be better protected from the next hurricane.