Building Pathology

Question 1

How would you advise a client if they were experiencing water ingress through a 10 year old single-ply flat roof covering?

Answer 1

• Check if the works are still covered by the guarantee.
• Electronic leak detection
• Thermographic Survey
• Can become contaminated through contact with bitumen below as plasticiser is lost and it become brittle. Normally an isolating membrane is used.
• Puncture damage - e.g. foot traffic
• Failure of welded seams due to poor workmanship.

Question 2

How would you identify Dry Rot, and reduce risk of it occuring in future?

Answer 2

• Life Cycle: spore, hyphae, mycelium, fruiting body
• Cuboidal cracking
• Spore Dust
• Lower moisture content
• TREATMENT: Heat and Ventilate, Remove area + 450mm, Presevative, Masonry sterilisation.
• PREVENTION: Ventilation, Treated Timber, Waterproofing

Question 3

How would advise a client if their timber sash windows were in poor condition?

Answer 3

• Heritage/conservation considerations
• Repair (resin) vs like-for-like replacement
• Replacement with better performing alternative?
• EPC considerations

Question 4

What are the limitations with thermographic surveys and moisture meters?

Answer 4

• Moisture meters generally calibrated to wood moisture content - are not accurate at determining moisture content in other materials - plaster, brick etc. But they do show a pattern.
• Moisture meters just test resistance so may pick up causes other than damp e.g. hygroscopic moisture.
• Thermographic surveys - not suitable for metal or glass that tend to reflect temperatures of surrounding buildings/objects.
• Thermographic surveys - need correct weather and temperature variance between internal and external.

Question 5

What is freeze thaw action?

Answer 5

When water fills voids of rigid porous material and then freezes and expands, causing material to crack and spall. The damage allows greater volumes of water to enter the material and the damage can become progressively worse.

Question 6

What types of stone are more susceptible to freeze thaw action?

Answer 6

• Those with a higher porosity e.g. limestone and sandstone, although those with particulalry large pore structure can allow water to evaporate more easily.
• Engineering bricks are less porous than common or facing bricks.

Question 7

Regent St - How did you determine freeze thaw was the cause of cracking rather than other types of movement?

Answer 7

• Cracks same size at either end.
• No rotational movement
• Walls plumb
• No evidence of other structural failure below.
• No evidence of thermal expansion or contraction at a junction or differential movement between materials.

Question 8

Is there any guidance that can be referred to for assessing cracks in low-rise buildings?

Answer 8

• BRE Digest 251 - categorised cracks into 6:
• 0 - negligible - up to 0.1mm
• 1 - fine cracks - up to 1mm
• 2 - easily filled cracks - up to 5mm
• 3 - cracks requiring some opening up - 5-15mm
• 4 - extensive damage requiring breaking out and replacement - 15-25mm
• 5 - structural damage - major rebuilding - greater than 25mm

Question 9

What is Carbonation?

Answer 9

• Reaction of Carbon Dioxide, Water and Calcium Hydroxide in Cement to create calcium carbonate.
• pH lowers and passive layer around reinforcement is broken down, and re-bar corrodes and expands.

Question 10

What specialist tests are there for identification of carbonation?

Answer 10

• Phenolphthalein - an alkalinity test.
• Pink result - pH is 13-14 = Good
• Clear result - pH 9 = Bad

Question 11

How would you specify repairs to concrete affected by carbonation?

Answer 11

• Hammer test
• Hack off all loose
• Grit-blast reinforcement to remove all corrosion
• Apply zinc-based primer to reinforcement
• Patch repair concrete
• Apply an anti-carbonation coating

Question 12

Can you give me 2 other concrete defects you might encounter on a 1960s concrete framed office building?

Answer 12

1. Chloride Attack - calcium chlorides used as an accelerator (also de-icing salts or exposure to marine env.) Effect same as Carbonation.
2. Sulphate Attack - dissolved salts penetrate into concrete from soil, groundwater etc and destroy with expansive effect. Remedy - install anodes with DC current. Cathodic protection with sacrificial zinc anodes.
3. High Alumia Cement - particularly with pre-cast beams. Widespread Use in 50s-70s. Banned in 1976 because it undergoes a transformation where it increases its porosity and loses strength. Can result in collapse.

Question 13

What are the 3 types of structural waterproofing protection for underground structures?

Answer 13

• Type A - Barrier Protection (tanking) - internal, external or sandwich. Liquid applied, cemetitious or bonded sheet.
• Type B - Structurally Integral e.g. Watertight Concrete
• Type C - Drained Systems - e.g. cavity or through egg-box membrane directing water away.

Question 14

What advice would you give for a basement car-park suffering water ingress from ground water for a repair strategy?

Answer 14

• A combination of a Type A and a Type C system so there is a back-up system in place.

Question 15

How would you identify and treat Woodworm / Furniture Beetle?

Answer 15

• Woodworm is the larvae of the the wood-boring beetle
• It creates 1-2mm circular holes with bore dust (frass) left by holes
• Found typically in floorboards, furniture, joists, beams, rafters
• Fairly damp conditions e.g. greater than 15% moisture content (wood boring weevil prefered even damper conditions)
• Treatment - requires Permethrin-based treatment, heating and drying area, cutting out and replacing affected sections.

Question 16

What defects would you typically associated with asphalt flat roof and how would you advise a client if defects found?

Answer 16

• Asphalt is ‘thermoplastic’ e.g. softens with heating and can shift and ‘slump’.
• Becomes hard and brittle with exposure to UV light.
• Large range transitions between hot and cold = cracking.
• Blistering is common - caused by poor detailing (particularly at upstands) allowing water ingress or lack of a VCL.
• When used over insulation, heat from UV is unable to dissipate downwards, which can create more softening and ‘flow’ of material.

Question 17

What is a ‘Deleterious Material’?

Answer 17

• Can be broad definition.
• Encompasses materials that lead to failure in building, and also materials that are dangerous to health.

Question 18

Can you give some examples of Deleterious Materials?

Answer 18

• Asbestos
• High Alumina Cement - see other card.
• Woodwool slabs when used as permanent shuttering - concrete was not compacted sufficiently leading to ‘honeycombed appearance that lost structural strength.
• Mundic Concrete - Common in Devon and Cornwall - mining waste used as aggregate in concrete breaks down in contact with moisture.
• Sea-dredged aggregates containing impurities

Question 19

What is Roof Spread?

Answer 19

• Rafters exert an outward horizontal thrust on external walls because they are not adequately supported, or because they are over-stressed.
• Common in Victorian or older properties which only had a tie half-way up rafters.
• Tie beams ( collar ties) often cut out as they got in the way.

Question 20

At Marlborough, why was a structural engineer required and what did they provide?

Answer 20

• Required to provide an assessment of the loadings being transferred from roof structure onto external walls, and confirmation this was causing outward movement.
• Provided design for new steel ‘channels’ for existing pulins to be placed in and for steel tie-rods to tie the channels together.

Question 21

At Marlborough, you describe ‘roof-spread caused by structural defects’, and that historic tie bracing and pattress plates were visible. What structural defects are you referring to here, and what others might have caused/be causing the issue? Was it progressive? What would advise the client if not progressive?

Answer 21

• Existing of tie-bracing and pattress plates suggest a historic issue.
• ‘Bulging’ of brickwork around pattress plates suggests possibly progressive - could be indicative that tie-bracing not providing enough restraint.
• Although no reports from occupants that issue is progressive, or suggestions of alterations that may have caused it e.g. changes to roof coverings.
• Internally, a purlin appeard ‘rotated’ - caused by changes in humidity or moiture levels - roof was not watertight.

Question 22

Explain the problems that may be encourntered with Magnesium Oxide boards?

Answer 22

• Rise in use over last 20 years. Often used as backing for brick slips or render.
• Poor manufacturing can lead to hygroscopic salts in the material which leads to them drawing in moisture from the atmosphere and contact with water.
• Can lead to moisture ‘leaking out’ and causing corrosion or damage to adjoining timbers.
• Problems often not seen as the boards are normally hidden.

Question 23

You are undertaking a pre-acw inspection of a 19th C house converted some time ago into offices and note the ground floor is ‘lively’ deflecting under foot. Describe possible causes, issues to the potential purchaser and remedies.

Answer 23

• Overloading due to increase in imposed loads.
• Lack of sub-floor ventilation causing decay to joist ends.
• Lack of damp membrane separating joist ends from masonry - rising damp.
• Insect infestation.
• Lack of noggins - or decay to noggins .

Question 24

What is a Nikel Sulphide Inclusion in glazing?

Answer 24

• An impurity resulting from the manufacturing process - small particles of nikel suplphide remain in the glass and will grow over time, causing sudden failure.
• ‘Butterfly’ cracking will occur from central point.
• Part K recommends glazing is ‘heat-soaked’ - a process reducing the liklihood of it occuring.

Question 25

Describe potential defect mechanisms that may lead to extensive map cracking or crazing within external render.

Answer 25

* Render is lime, sand and cement. When lime not used, risk of shrinkage cracking as render is not flexible enough. This leads to crazing.

Question 26

At high street Ilfracombe you stated that the cause of damp was penetrating damp, can you discuss other causes of moisture ingress briefly?

Answer 26

* Rising damp - caused by dynamic movement of water through a wall based on a number of factors. Presence of salts within wall, temperature of wall, level of saturation in the ground, can all affect how quickly the water * Condensation. Caused by a lack of ventilation and a ready source of water vapour.

Question 27

Can you tell me some typical crack patterns and what they might indicate?

Answer 27

*Horizontal cracking to brick work/stone wall tie failure (cavity walls) Regents street disease *Stepped cracking wider at bottom than the top Heave *Stepped cracking wider at the top than the bottom throuhg brick and mortar subsidence *Stepped cracking either side above a lintel/brick arch lintel failure *Hairline cracking at wall and ceiling joints Shrinkage Settlement - usually of a new build *Large 5mm+ cracks or multiples of 3mm between a house and an extention or a bay window Differential movement. *Vertical cracking on a steel framed structure or between two different materials thermal expansion

Question 28

What is Reinforced Autoclaved Aerated Concrete?

Answer 28

Pre-cast panels, commonly used in eduction establishments in flat roof construction, walls and floors. Is a deleterious material that will lose strength due to lack of larger aggregates to bind it. Department of Education has released information about it.