Pathology Of Walls Flashcards
Lateral instability in walls.
The middle third rule
Latural instability of walls:
Measuring a bulge
Lateral instability of walls:
For a 225 mm thick wall, the width of the middle third will be 75 mm:
Wall tie corrosion is considered at serious risk through to:
All pre war cavity wall housing and postwar housing through to 1982
Things to consider in identifying the risk or presence of wall tie corrosion:
Identifying remedial wall tie holes
- Standard cavity wall 900 mm horizontal 450 mm vertical
- For wider cavities dinner masonry or residential high-rise is 450 x 450 mm
- At window/door reveals and verges of any Gables 300 mm vertically
- Timber frame houses only vertical at around 450 to 600 mm vertical centres
Sulphate attack in brickwork.
What are the causes:
Identifying sulphate attack in brickwork:
Sulphate attack in chimney stacks:
Expansion of brickwork causes movement and cracks
Expansion of brickwork causes movement and cracks
Thermal movement of bricks:
Support over openings:
Deflection of bressumer beams
Overloaded elements
Crack monitoring
A surveyors approach to assessing building movement. BREs digest 251 Five stages of assessment:
Assessing building movement – looking for signs of movement:
- Sloping floors or windowsills
- Distorted openings and windows
- Obvious signs of movement in or around site
- Unevenness in paths roads and so on
Golden rule of crack interpretation No 1
- Cracking is usually but not always perpendicular to the direction of the movement
- Therefore horizontal cracks usually indicate vertical movement (e.g. creep deflection, tie failure, etc)
- Vertical cracks usually indicate horizontal movement (e.g. thermal or moisture)
Golden rule of crack interpretation No 2
- If a foundation moves then all walls resting on it will also move
- Cracks are associated signs of movement should be visible on both sides and, or both leaves if the cools is foundation movement
- Movement can result in gaps, as opposed to cracks
Golden rule of crack interpretation No 3
- Cracks are usually wider more frequent, closer to the focus of the movement
- However, always try to corroborate a theory with other evidence – especially out of plumbness
Look for the most likely suspects.
These may include:
- Trees and stumps – which are responsible for 85% of subsidence issues
- Drain pipes, manhole covers, and hydrants – which are responsible for 15% of subsidence issues
- Scars in the pavement (under mining)
- Long walls without joints or openings (shrinkage or expansion)
- Tall sections of wall (lack of restraint)
- Corroding steel components
Settlements usually stops after 10 years:
- Settlement is movement caused purely by the weight of the building
- Subsidence is caused by an extraneous factor – tree, drain, mine, etc
- So if you see recent cracks in an old building and you think they are due to foundation movement, and the cause is unlikely to be settlement
So what are the indicators of further movement?
Following causes account for 80 to 90% of all subsidence cases:
- Nearby shrubs or trees
- Proximity of sloping ground
- The possibility of leaking drains
- Susceptible soils – shrinkable clay is
Fence sitting – avoid it!
Table category damage to buildings using the ‘ease of repair’ approach
