Building Pathology Flashcards
Can you describe the common causes of damp and cracking in buildings and their potential impact on the building fabric?
Answer: Damp can be caused by various factors, including poor drainage, leaking pipes, and rising damp from the ground. It can lead to problems such as mold growth, timber decay, and deterioration of wall finishes. Cracking in buildings can result from structural movements, such as settlement, thermal expansion, or moisture changes. These cracks can compromise the building’s structural integrity and aesthetic appearance, and if not addressed, they may lead to more severe damage or safety issues.
How do you differentiate between various types of cracking (e.g., settlement cracks, thermal cracks) and what are their underlying causes?
Answer: Settlement cracks typically occur shortly after construction as the building settles into its foundation. They are often vertical or diagonal and may be wider at the top than the bottom. Thermal cracks result from temperature fluctuations causing expansion and contraction of building materials. They usually appear as fine, hairline cracks and are often vertical. Differentiating these types involves assessing their location, width, and progression over time, along with understanding the building’s construction and environmental conditions.
What are the potential structural and functional impacts of dampness on a building’s fabric and how might it affect the occupants?
Answer: Dampness can weaken the building fabric by causing timber decay, corrosion of metal components, and deterioration of plaster and masonry. It can lead to structural problems such as weakening of load-bearing walls. For occupants, dampness can cause health issues like respiratory problems and allergies due to mold and mildew growth. It also affects the building’s energy efficiency and comfort levels by increasing heating costs and causing unpleasant odors.
At what interval should expansion joints be?
- Concrete walls – 9 to 18 meters
- Brick walls – 6 to 9 meters horizontally and 6m vertically for walls over 9 meters high.
How do you assess the severity of defects like damp and cracking during a building inspection?
Answer: Assessing the severity of damp involves using moisture meters to measure the moisture content in walls and floors. I also look for signs of mold, peeling paint, or damp stains. For cracking, I measure the width and length of the cracks, note their location and direction, and observe any signs of ongoing movement. BRE Digest 251 I consider the building’s age, construction type, and any recent alterations or environmental conditions. Detailed observations are documented to help determine the required remedial actions.
Explain these terms to me; heave / seasonal movement / settlement / shrinkage / subsidence / thermal movement.
Heave:
Heave refers to an upwards movement of the ground beneath the structure forcing the foundation up
Caused by changes in soil moisture content (tree removal), freeze thaw cycles, expansive soil conditions.
Signs usually cracks in walls, often tend to be vertical, and around openings. Doors and windows may become difficult to close. Uneven floors.
Rectification can be done by foundation repair, underpinning. Implement measures to manage the moisture content in the soil such as drainage provisions or directing surface water away from the building. Soil stabilisation, improve its strength by adding cement or lime.
Seasonal Movement:
Refers to the cyclic expansion and contraction of building materials and components in response to seasonal changes in temperature, humidity and moisture levels. Effects foundations, walls, floors, roofs and may lead to cracking and distortion.
Caused by temperature changes, in warm materials expand and contract in colder weather. Humidity and moisture affect materials such as wood, masonry and concrete causing swelling and shrinkage, leading to dimensional change and movement. Soil conditions, the added moisture can affect the soil and cause it to contract causing the foundations to move.
Signs usually include cracking, uneven floors and doors becoming difficult to open.
Settlement:
Refers to the gradual downwards movement or compression of the ground beneath the structure, resulting in the foundation settling lower than intended. Some settlement is expected within the first 12 months of build completion.
Caused by soil composition, expansive soils undergo significant volume change in response to moisture content, can experience swelling and shrinkage leading to uneven settlement. Foundation design, if the foundations are poorly design or constructed and not suitable for the soil. Building loads. Excess water in the soil directly around the property.
Signs include cracking in any direction, usually stepped, uneven floors, tilting or leaning structural elements.
Shrinkage:
Refers to the shrinkage of building materials due to a loss of moisture, which can happen at any stage in a building’s life cycle.
Concrete – Has both chemical shrinkage and drying shrinkage. Chemical shrinkage occurs during the hydration process, when water reacts with cement causing the concrete to contract. Drying shrinkage occurs when water evaporates from the concrete leading to further shrinkage.
Wood – Humidity level effects wood.
Clay shrinkage – shrinkage occurs as they dry out or lose moisture. Leading to cracking.
Leads to cracks and separation of building elements, warping and distortion.
Expansion joints should be used to prevent damage from expansion and contraction, as well as DPMs.
Subsidence:
Refers to the downwards movement of the ground beneath a structure, leading to the lowering of a buildings foundations relative to their original position. Subsidence can occur gradually over time, or suddenly. Can have a significant impact on the stability and safety of a building.
Causes are natural soil settlement, changes in the soil moisture levels. Swelling or shrinking of expansive soils can lead to subsidence or heave. Groundwater fluctuations, excessive extraction, seasonal variation in precipitation, or changes in drainage patters can lead to the soil drying and subsidence occurring. Leaking or broken underground pipes can undermine the foundations causing localised settlement. Mining.
Signs are diagonal stepped cracking.
To address subsidence you must stabilise the foundation, professional consultation would be required from structural engineers, geotechnical engineers to determine the exact cause and remediation.
How would you fix expansion cracking?
- Determine the location of the expansion joints (6m).
- Select the correct material such as preformed filler or compressible foam.
- Saw cut a gap between the brickwork and insert the expansion joint material.
How would you identify and diagnose wall tie failure?
Often can be done by visual inspection:
- Horizontal cracking to brickwork at 450mm intervals.
- Bulging or bowing walls
- Separation between the building and frame.
- Rust stains or corrosion around wall tie location.
- Loose or missing mortar particularly around wall ties.
Wall tie testing:
- Pull out testing: applying a pulling force to wall ties to test the tensile strength,
- Inserting a borescope or endoscope into the wall cavities to visually inspect the condition of the wall ties.
What is the spacing of wall ties?
Horizontal 900mm max and vertical 450mm max. Around openings 225mm away from window or door and 300mm spacing
What type and age of wall ties are liable to wall tie failure?
Steel ties made of mild steel are susceptible to corrosion over time, especially in high moisture and salt contents. Corrosion weakens ties and leads to failure. Galvanised ties are more resistant, but over time will still fail. Stainless steel ties offer superior resistance.
Building located in coastal areas and old buildings with traditional ties are most likely to fail.
Black ash mortar contains sulphate which can react with moisture and components of the mortar to produce sulfuric acid. The acidic environment accelerates the corrosion of mild steel wall ties. Typically on buildings between 1920s and 1960s and mortar is often darker in colour.
How would you identify rising damp?
Visual signs include the following:
- Tide marks up to 750mm - 1m above the floor.
- Bubbling paint/plaster.
- Salt deposits where water evaporates, leaving salt behind.
When and why might it occur?
Rising damp occurs primarily due to the absence or failure of a damp proof course, allowing moisture from the ground to be drawn upward through porous building materials via capillary action. It’s more prevalent in older buildings with solid walls, especially in areas with high groundwater levels, poor drainage, and porous building materials. Rising damp is most likely to occur after periods of heavy rainfall, during high humidity, and in the cooler
How and why might a DPC fail?
- Physical damage through construction, cutting into the DPC material etc.
- DPCS such as felt, plastic membranes or slate can deteriorate over time.
- Poor installation (not 150mm above) can cause the DPC to be bridged.
- Bridging by internal finishes, if finishes below dpc the damp bricks below the dpc will penetrate to internal finishes and rise up.
What is the role of a moisture meter in diagnosing damp issues in a building, and how do you interpret its readings?
Answer: A moisture meter helps identify areas with elevated moisture levels that may indicate damp problems. It measures the moisture content in building materials, which is crucial for diagnosing the extent of dampness. Readings are interpreted by comparing them to established thresholds for normal and damp conditions. High moisture readings indicate potential damp issues that require further investigation and remediation. 18-20% and above are gernerally concerning readings.
Can you explain how crack monitoring devices are used to track the movement of cracks and assess their severity?
Answer: Crack monitoring devices, such as crack gauges or transducers, are placed across cracks to measure any movement over time. These devices track changes in the width of the crack and provide data on its progression. By regularly monitoring the crack’s movement, I can assess whether it is stable or widening, which helps in determining the severity and potential causes of the cracking and in planning appropriate remedial measures.
How do you select the appropriate equipment for different types of defects, and what factors influence your choice of tools during an inspection?
Answer: The choice of equipment depends on the type and location of the defect. For damp issues, I use moisture meters and thermal imaging cameras to detect hidden moisture and heat patterns. For cracking, I use crack monitoring devices and tape measures to assess the size and progression. Factors influencing my choice include the specific nature of the defect, the materials involved, the accessibility of the affected areas, and the level of detail required for accurate diagnosis.
What are some limitations of the equipment you use in building pathology, and how do you mitigate these limitations in your assessments?
Answer: Limitations include the potential for false readings with moisture meters due to different material types and moisture content variations. To mitigate this, I cross-check readings with visual inspections and consider environmental factors. Crack monitoring devices may only show movement at the device location and not the entire crack length, so I use multiple devices and conduct thorough visual assessments to get a comprehensive view of the crack’s behaviour.
What are the key causes of cut edge corrosion in industrial roofs, and how does it impact the roof’s performance?
Answer: Cut edge corrosion typically results from the exposure of cut edges of metal roofing sheets to moisture and environmental elements. Over time, this leads to rust and degradation of the metal, weakening the roof’s integrity and causing leaks. The corrosion can compromise the roof’s durability, lead to water ingress, and result in further damage to the building’s interior and structure.
How do you identify cut edge corrosion during an inspection, and what visual or diagnostic indicators should you look for?
Answer: Cut edge corrosion is identified by inspecting the edges of metal roofing sheets for signs of rust, peeling paint, and deterioration. Visual indicators include discoloration, flaking of the protective coating, and rust stains. I also check for any evidence of water ingress or leaks that may be associated with corrosion. Using a magnifying glass or corrosion testing kit can help identify early signs of cut edge corrosion.
How did the CPD session on cut edge corrosion influence your approach to diagnosing and managing this defect in your projects?
Answer: The CPD session enhanced my understanding of the causes and early signs of cut edge corrosion, as well as effective repair techniques. It has influenced my approach by increasing my awareness of the importance of early detection and the application of appropriate maintenance strategies. I now incorporate more detailed inspections and consider advanced repair methods based on the knowledge gained from the session.
What are the recommended repair techniques for cut edge corrosion, and how do these techniques address the underlying issues?
Answer: Recommended repair techniques include cleaning the affected areas to remove rust and debris, applying a rust-inhibiting primer, and then coating with a suitable protective paint or sealant. In severe cases, replacing the corroded sections may be necessary. These techniques address the underlying issues by stopping the corrosion process and restoring the protective coating to prevent further damage.
Can you provide an example of a project where you identified and managed a defect such as damp or cracking? What steps did you take to address the issue?
Answer: On a recent project, I identified rising damp in a building’s ground floor due to inadequate damp-proofing. I used a moisture meter to assess the extent of dampness and documented the affected areas. I recommended the installation of a new damp-proof course and improved drainage around the building’s perimeter. The work was carried out by a specialist contractor, and I monitored the progress to ensure that the remedial measures were effective and the problem was resolved.
How do you incorporate the knowledge gained from CPD sessions into your daily practice when dealing with building defects?
Answer: I apply knowledge from CPD sessions by implementing the latest techniques and best practices into my inspections and assessments. For example, insights from a CPD session on cut edge corrosion led me to use more precise diagnostic tools and to follow updated repair protocols. I also share this knowledge with colleagues and integrate it into client reports and recommendations to ensure that we provide up-to-date and effective solutions.
Can you explain the potential causes and impacts of vertical cracking in masonry, and how you determined that expansion was the likely cause in the Worksop property?
Answer: Vertical cracking in masonry can be caused by several factors, including structural settlement, thermal expansion, or moisture-related movement. In the Worksop property, the vertical cracking through both the mortar joints and brickwork suggested that the cracking was due to expansion. The absence of expansion joints in the large masonry wall indicated that the wall was not designed to accommodate thermal movement, leading to the observed cracks. The impact of such cracks includes potential weakening of the wall’s structural integrity and aesthetic issues. My assessment involved reviewing the construction details and considering environmental factors such as temperature fluctuations that could contribute to expansion.
Describe a situation where the use of moisture meters or crack monitoring devices significantly enhanced your understanding of a building defect.
Answer: During an inspection of a historic building with persistent damp issues, the moisture meter provided crucial data on the moisture levels behind wall finishes. This data helped to pinpoint the source of the damp problem and guided the decision to replace a damaged section of the building’s damp-proof course. Crack monitoring devices were used to track the movement of cracks in a newly constructed building, allowing for timely intervention and stabilization measures before significant damage occurred.
How do you communicate the implications of building defects to clients, and what recommendations do you typically provide to address these issues?
Answer: I communicate the implications of building defects by presenting a clear and concise report that outlines the nature of the defects, their potential impact on the building, and any associated risks. I provide recommendations for remedial actions, including repair techniques, estimated costs, and timelines. I ensure that the recommendations are practical and aligned with the client’s budget and objectives. Additionally, I explain the importance of addressing the defects promptly to prevent further damage and additional costs.
