Building Pathology

Question 1

What is building pathology?

Answer 1

The study of building defects, performance and failure resulting in the remedies

Question 2

What is the purpose of a condition survey and what are the associated drawbacks?

Answer 2

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

Question 3

Explain wall tie failure

Answer 3

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

Question 4

What is sulphate attack in brickwork?

Answer 4

a. Reaction between sulphates and Portland cement
b. Causing crumbling of mortar and expansion of wall

Question 5

How would you identify wall tie failure vs sulphate attack?

Answer 5

Wall tie failure you would see horizontal cracking at courses every 450mm vertically whereas sulphate attack could occur in every course

Question 6

Explain a 1920s traditional built house

Answer 6

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

Question 7

Typical defects in traditional built house - top-down approach

Answer 7

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

Question 8

What are common defects found on a Victorian Property?

Answer 8

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

Question 9

Why do mortar fixings fail to roof?

Answer 9

a. Mortar has a limited time span
b. Less durable to movement

Question 10

What is the make-up of a flat roof?
Warm = JTVIR
Cold = JITR

Answer 10

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

Question 11

Defects to flat roofs?

Answer 11

a. Splitting of covering
b. Sagging (failed decking between joists)
c. Ponding
d. Damage to flashing

Question 12

What is interstitial condensation?

Answer 12

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

Question 13

Explain each type of damp?

Answer 13

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

Question 14

How does black mould form?

Answer 14

High humidity, lack of ventilation and lack of heating causes airborne moisture to condensates on the colder surfaces

Question 15

How do you undertake a carbide test?

Answer 15

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

Question 16

Explain BRE Digest 245?

Answer 16

a. Guidance on diagnosis and treatment of rising damp in walls
b. Guidance on carbide test

Question 17

Explain limitations of equipment

Answer 17

Moisture metre: normally used for moisture in wood, only take surface level moisture

Question 18

What are the two types of rot?

Answer 18

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

Question 19

What are common defects found on masonry/brickwork walls?

Answer 19

a. Brick spalling
b. Thermal movement
c. Rising/penetrating damp
d. Wall ties failure

Question 20

Explain thermal movement

Answer 20

Occurs when two areas to a masonry wall expand or contract at different rates causing hairline cracks

Question 21

Explain frost attack

Answer 21

Water entre voids in brickwork, freezes and expands causing brick spalling

Question 22

Explain sulphate attack in concrete

Answer 22

a. Chemical reaction causing concrete to expand and crack due to the penetration of sulphates from ground water
b. Use resistant concrete to avoid

Question 23

Explain BRE Digest 251

Answer 23

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)

Question 24

Explain types of cracks seen on brickwork walls due to ground/foundation movement?

Answer 24

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.

Question 25

What is a cold bridge?

Answer 25

Area of a wall that is thermally different such as solid concrete or debris in the cavity causing an internal cold spot

Question 26

What is lintel failure?

Answer 26

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

Question 27

What is lintel corrosion?

Answer 27

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.

Question 28

Explain BRE Digest 461

Answer 28

Gives information surrounding the defect of the corrosion of metal components in walls (particularly wall ties), as well as remedial methods

Question 29

What can render that is bridging the DPC cause on a cavity wall?

Answer 29

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.

Question 30

What detail should be at low level of a render system?

Answer 30

A drip detail/drip bead