Building Pathology Flashcards
What is building pathology?
The study of building defects, performance and failure resulting in the remedies
What is the purpose of a condition survey and what are the associated drawbacks?
a. Purpose:
i. Up to date overview of the condition of a property including age and condition of elements
ii. Highlight any defects to property
iii. Aids with planned maintenance/project work and lifecycle costing
b. Drawbacks:
i. Snapshot in time
ii. Dependant on the detail of inspection
iii. Does not include costing and access limitations to property/areas
Explain wall tie failure
a. Corrosion of walls ties causing expansion upwards then outwards, seen through cracking in brickwork 900mm horizontally and 450mm vertically
b. Most common in properties between 1920 and 1981 where zinc coating was thicker
What is sulphate attack in brickwork?
a. Reaction between sulphates and Portland cement
b. Causing crumbling of mortar and expansion of wall
How would you identify wall tie failure vs sulphate attack?
Wall tie failure you would see horizontal cracking at courses every 450mm vertically whereas sulphate attack could occur in every course
Explain a 1920s traditional built house
a. Strip or slab foundation
b. Cavity wall construction
c. Concrete floor or suspended timber
d. Cut roof timber structure
e. Slate or concrete roof coverings
Typical defects in traditional built house - top-down approach
a. Blocked guttering
b. Issues to mortar
i. Too weak = not durable, too strong = cracks
c. Defective/absent DPC - cause rising damp
d. Penetrating/condensation damp
e. Subsidence or settlement causing building movement
What are common defects found on a Victorian Property?
a. Damp issues
b. Roof defects from slipped tiles
c. Timber rot (dry/wet/insect)
d. Structural issues either wall tie failure or foundation movement
Why do mortar fixings fail to roof?
a. Mortar has a limited time span
b. Less durable to movement
What is the make-up of a flat roof?
Warm = JTVIR
Cold = JITR
a. Warm roof: Joists, timber deck, vapour layer, insulation and roof covering
i. Allows moisture to escape but is more difficult to install
b. Cold roof: Joists with insulation between, timber deck and roof covering
i. Easy to insulate and cost effective
Defects to flat roofs?
a. Splitting of covering
b. Sagging (failed decking between joists)
c. Ponding
d. Damage to flashing
What is interstitial condensation?
a. Happens within buildings elements where there is a temperature difference
b. If temperature drops, moisture meets dew point and makes the internal of the material damp due to lock of ventilation/insulation
Explain each type of damp?
a. Rising damp: Tide marks up to 1/1.5m and peeling wall finishes
b. Penetrating: Moisture moves from exterior to interior through wall/mortar due to wind-driven rain or problems with DPC
c. Condensation damp: explain this
How does black mould form?
High humidity, lack of ventilation and lack of heating causes airborne moisture to condensates on the colder surfaces
How do you undertake a carbide test?
a. Used to measure moisture levels in masonry and completed at lowest point on wall possible
b. Drill into masonry and collect 6g of dust into container with calcium carbide
c. Moisture reacts and produces gas
d. Reading shown on device.
e. If too aggressive with drill, can evaporate the moisture in the wall
Explain BRE Digest 245?
a. Guidance on diagnosis and treatment of rising damp in walls
b. Guidance on carbide test
Explain limitations of equipment
Moisture metre: normally used for moisture in wood, only take surface level moisture
What are the two types of rot?
a. Dry - 20-30% moisture
i. Visible orange/brown spots of fungal decay not localised to one area
ii. Breaks in hand
iii. Bre Digest 299
iv. Investigate cause, removed affected timber, apply fungi wash
b. Wet - 50%+ moisture
i. Discoloured fungal decay which is more localised
ii. Spongy feel
iii. Bre Digest 345
iv. Fungi wash usually all that is needed, sometimes need to remove timber
What are common defects found on masonry/brickwork walls?
a. Brick spalling
b. Thermal movement
c. Rising/penetrating damp
d. Wall ties failure
Explain thermal movement
Occurs when two areas to a masonry wall expand or contract at different rates causing hairline cracks
Explain frost attack
Water entre voids in brickwork, freezes and expands causing brick spalling
Explain sulphate attack in concrete
a. Chemical reaction causing concrete to expand and crack due to the penetration of sulphates from ground water
b. Use resistant concrete to avoid
Explain BRE Digest 251
a. Assessing cracks in houses by giving potential causes through categorising
b. 5 categories of cracking set out the layout and the seriousness (0 = hairline cracks under 0.1mm - 5 = Structural damage)
Explain types of cracks seen on brickwork walls due to ground/foundation movement?
a. Subsidence
i. Downward movement in ground due to loss of support from soil - removal of water through tree roots or drains leaking
ii. Causes step cracking thicker at top and thinner at bottom.
b. Heave = ground below property expands and pushes upwards,
c. Settlement
i. Downward movement due meeting the new bearing capacity of the soil after new buildings built
ii. Causes stepped cracking thicker at top and thinner at bottom.
d. Differential settlement
i. One part of structures foundation settles more/faster than the other causing the structure to tilt slightly.
What is a cold bridge?
Area of a wall that is thermally different such as solid concrete or debris in the cavity causing an internal cold spot
What is lintel failure?
a. Caused by the corrosion or decay of lintels either due to the elements, or imposed loads from above.
b. Causes vertical stepped or v shaped cracking around the opening normally sourcing from the sides of the lintel
What is lintel corrosion?
a. Where steel lintels edge gets exposed it can corrode over time and expand causing brickwork to lift,
b. Vertical/V shaped cracking surrounds masonry around the opening.
Explain BRE Digest 461
Gives information surrounding the defect of the corrosion of metal components in walls (particularly wall ties), as well as remedial methods
What can render that is bridging the DPC cause on a cavity wall?
a. Promotes frost attack
b. Hairline cracks at DPC level caused by differential thermal movement of brickwork above and below the DPC which can then allow water ingress.
What detail should be at low level of a render system?
A drip detail/drip bead
