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RICS APC Revision > Building Pathology L1-3 > Flashcards

Building Pathology L1-3 Flashcards

1
Q

WHAT IS A VISUAL INDICATOR OF CARBONATION IN REINFORCED CONCRETE?

A

Carbonation causes complete dissolution of the brick protective layer, caused by carbon dioxide in the atmosphere.

The expansion of corroded / rusting steel will result in cracking and spalling of the surface concrete.

This can take several years to take effect on concrete, causing durability issues.

Site test - Solution used to indicate the alkaline level of the concrete, if pink, the concrete is not yet carbonated.

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2
Q

WHAT ARE THE CAUSES FOR FLAT ROOF DEFECTS?

A

Cracking - Lack of protection from the sun / chemical attack

Ponding - Lack of sufficient gradient

Thermal movement - Movement between substrate and membrane

Blistering - Water vapour pressure below roof covering

Flashing / Falls / Detail deterioration or movement

Poor workmanship - Lack of quality in base build or repair

People - By personnel or loose debris

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3
Q

WHAT ARE THE REMEDIES FOR FLAT ROOF DEFECTS?

A

Crazing - Localised repair or full replacement with specialist protection

Ponding - Inc. in gradient and re-covering

Thermal movement - Replace with high performance felt

Blistering - Remove trapped moisture, trace, repair

Flashing / falls - Replace flashing around falls / junctions

People - Avoid footfall / debris building on roof

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4
Q

NAME METHODS OF ASSESSING FLAT ROOF DEFECTS?

A

Electronic leak detection - Weak electrical field on dampened surface to find ‘earths’ into the building, pinpointing penetration point or show water ingress is not caused by a roof leak.

Thermographic examination - Thermographic image highlights areas of moisture retained within the roof to pinpoint location of leak.

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5
Q

WHAT ARE THE COMMON DEFECTS ASSOCIATED WITH FLAT ROOFS?

A

Blistering

Splitting of coverings

Sagging due to failure of the decking between joists

Ponding due to insufficient falls

Damage to flashings

Thermal movement

Crazing

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6
Q

WHAT SHOULD BE TAKEN INTO ACCOUNT WHEN CONSIDERING REPAIR / REPLACEMENT OF A FLAT ROOF?

A

Current age, life expectancy and overall condition

Surveyor should consider the current condition, number / spread of defective areas i.e. localised or widespread, and whether the defect is effecting the surface layer roof structure

Clients intention for the building, the available budget, the building use, disruption caused by repair and possible phasing requirements

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7
Q

HOW WOULD TOU APPROACH A FLAT ROOF INSPECTION?

A

Desktop survey - Gather site info i.e. age, construction, current or previous works to the building

Arrange access and prepare RAMS

Attend site to assess the roof:
- Age
- Previous repairs undertaken
- When and where the roof leaks
- Ponding issues
- Room use beneath
- Footfall frequency

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8
Q

WHAT IS DAMP?

A

A building is considered to be damp when moisture becomes visible through discolouration and staining of finishes, or causes mould growth, sulphate attack, frost damage or drips / puddles

Building regulations for DPCs were developed in early 1900’s but were not always adhered to

Types of damp:
- Condensation
- Rising damp
- Penetrating damp
- Services caused

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9
Q

SIGNS OF RISING DAMP?

A

Internal:
- Unsightly efflorescence
- Wallpaper peeling / visibly damp walls up to 1m
- Blistering
- Decaying skirting boards
- Black, white and green mould growth on walls

External:
- Render degradation
- Efflorescence
- Discolouration
- Cracks in masonry
- Bricks and mortar deterioration

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10
Q

CAUSES OF RISING DAMP?

A

Internally rising groundwater saturates walls with Saltpetre (contained in water)

Damaged or lack of DPC

Via capillary action in masonry

Ground level higher than existing DPC

Cold bridging

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11
Q

WHAT IS A COLD BRIDGE?

A

Weak points in the building envelope allowing heat to pass through more easily, e.g. the roof / wall junction or wall / floor junction. Colder areas not insulated will cause condensation in warmer living areas

Sign - Formation of black mould around skirtings / window openings

Cause - Warm surface or structure meets cold one

Remedy - Eliminate thermal bridge, reducing cross-section with better insulation materials or with a thermal break

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12
Q

REMEDIES OF RISING DAMP?

A

Retrospective / replacement of the DPC

Exterior moisture barrier, inc. excavation down to foundations if the rising damp is permanent

Improve ventilation

Control excess water

Sealing up cracks and moisture barriers

Replace rotting joists / internals affected by damp

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13
Q

SIGNS OF PENETRATING DAMP?

A

Blistering / damaged plaster and wall finishes

Localised dampness

Mould growth

Wet rot affecting floor & wall timbers / skirting boards

Commonly found in roofs, window openings, door openings, brick / stone elevations

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14
Q

CAUSE OF PENETRATING DAMP?

A

Defective porous external envelope:

  • Roof, brick / stone elevations (insufficient thickness i.e. one brick thick)
  • Cavity the mortar snot bridge external to internal wall
  • Cavity tray defective
  • Window / door opening
  • Missing pointing or render
  • Faulty rainwater goods (often cast iron)

External envelope can deteriorate with age, frost or physical damage, promoting penetrating damp

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15
Q

REMEDIES OF PENETRATING DAMP?

A

Re-pointing affected areas, lime mortar preferred for old buildings (highly breathable to allow evaporation of existing moisture)

Fixing cracks / gaps in external envelope

(Consider roof, chimney, parapet, junctions, windows, doors, brick / stonework)

Repair / replace rainwater goods

Inspect and repair / replace cavity trays & cavity ties (blockages)

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16
Q

HOW IS A DAMP SURVEY UNDERTAKEN?

A

Consider building materials, age, locality

Note timescale of damp presence, when it occurs, ay changes since the damp appeared

Methodically check localised areas, i.e. substructure, superstructure, roof void, openings etc from internal & external

Use of devices to monitor moisture levels of materials i.e. Protimeter

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17
Q

WHAT IS MOULD GROWTH?

A

Fungal growth developed on wet material in interior spaces

The primary reason within a building is uncontrolled moisture incursion in the form of liquid flow, condensation, high humidity or capillary action (moisture travelling through building elements via surface tension, against gravity)

Gaps in external envelope

Defective rainwater goods

Occupier use i.e. cooking / drying clothes

18
Q

WHAT ARE THE BENEFITS OF USING LIME MORTAR?

A

Highly breathable for older, moist buildings

Adhesion properties

Flexible to allow thermal and building movement

Regulates building humidity due to porous properties

Protective layer against frost and water movement due to high quality bonding, reducing water ingress risk

Highly workable during applications

Highly versatile and durable

19
Q

WHAT IS FROST DAMAGE / ATTACK?

A

Physical process causing deleterious effect on porous brick / stone / concrete due to cyclical freezing & thawing

Course-grained materials sock moisture, undergoes volumetric expansion causing deterioration of the surface (spalling)

Common areas are those exposed to elements, often saturated i.e. parapets and below the DPC and ground level

20
Q

HOW TO REMEDIATE FROST DAMAGE / ATTACK?

A

Proactive - Ensure constant drainage, no pooling or continuous damp patches to external envelope

Developed attack - Remove and replace affected bricks, re-point with breathable mortar i.e. lime

New attack - Re-point with breathable mortar to allow moisture to evaporate

21
Q

WHAT ARE THE STAGES OF DAMP?

A

Stage 1 - Visual inspection

Stage 2 - Investigation using moisture meters

Stage 3 - Detailed investigation

Stage 4 - Locating the source

22
Q

HOW CAN YOU TEST FOR DAMP?

A

Protimeter works by measuring electrical resistance between two electrodes

Protimeters are only accurate measuring moisture content in timber

Other materials gain misleading readings, however, can be used to gain a sense of moisture content

Less accurate than a speedy carbide meter

23
Q

WHAT IS A SPEEDY CARBIDE METER?

A

Measures moisture content in aggregates, ceramics, abrasives (masonry)

Drill masonry to place dust in a sealed container with a measurement of calcium carbide to confirm moisture content

Dust and calcium carbide releases gas in proportion to the moisture amount present

24
Q

DESCRIBE 3 ISSUES AND REMEDIES FOR RISING DAMP

A

Issues:
- Lack of DPC
- Defective DPC
- External features bridging the DPC

Remedy:
- Remove external feature causing bridging, injection of water repellent chemicals into brickwork or installing a new DPC layer

DPC not suitable?
- Lime plaster and wash applied externally to minimise damage

25
Q

WHAT IS CONDENSATION AND HOW IS IT CAUSED?

A

Hot air carries moisture, condenses on cold surface and leaves water droplets on surface

Source - breathing, domestic activities, cooking, eating

Leads to staining at cold bridges, peeling wallpaper & mould growth

Causes:
- Lack of insulation, lack of ventilation and unheated areas of a building

Common areas - Bedrooms, kitchens, bathrooms

26
Q

HOW TO REMEDIATE CONDENSATION?

A

Reduce moisture generation

Provide adequate ventilation & heating

Improve building insulation

27
Q

HOW LONG WOULD YOU LEAVE BRICK & MORTAR TO DRY OUT PRIOR TO COMMENCING WORKS?

A

De-humidifier can speed up the process, however 3-4 months minimum recommended

28
Q

TALK ME THROUGH YOUR THOUGHT PROCESS… NUMBER OF CRACKS IN AN EXTERNAL WALL

A

Note wall material, building form and approx. age

Local factors:
- Trees
- Stumps
- Drainage in the vicinity of the crack inc. rainwater
- Previous alterations to the building

29
Q

WHAT CAUSES CRACKS IN BUILDINGS?

A

Subsidence

Heave

Settlement

Differential settlement

Lintel failure

Corroded steel lintel

30
Q

WHAT IS SUBSIDENCE?

A

Ground beneath a building sinks, pulling the property’s foundation with, caused by:

Loss of soil moisture due to dry spells, more so in clay, adjacent tree introduced

Tell tale signs:

Internal - Cracks in walls, sinking floors, sticking doors / windows

External - Vertical cracking at centre, diagonal cracks at corners, larger at the top / thinner at bottom, dry soil, trees within vicinity, leaning building, extension seperated

31
Q

WHAT IS HEAVE?

A

Upward movement in floor slab due to soil movement beneath, inc. in moisture content i.e. removal of a tree in clay soil, or freezing forces

More common in floor slabs than foundations as slabs have less weight to resist heaving forces

Tell tale signs:

Vertical cracking at centre of building, diagonal cracking at corners, larger cracks at base of building / thinner at top

32
Q

WHAT IS SETTLEMENT?

A

Downward movement of a new build property consolidating or displacing the soil. This can occur a few years after completion of the build, dependant on:

  • Existing soil conditions
  • Methods of construction
  • Size and depth of construction
  • Type of structure, its condition and foundations

Opposite to heave, different to subsidence which is unstable soil

33
Q

WHAT IS DIFFERENTIAL SETTLEMENT?

A

Occurs when one part of a structure’s foundation settles more, or faster, than the other (uneven).

If one edge moves more than another, the structure tilts, i.e. Leaning Tower of Pisa

34
Q

SYMPTOMS OF DIFFERENTIAL SETTLEMENT?

A

Improper fit & function of doors and windows

Cracks and deterioration of foundations and slabs

Damage to walls and flooring

Structural instability, may be deemed unfit for occupation

35
Q

WHAT SIZE CRACKS ARE OF CONCERN?

A

Up to 2mm - very slight concern

2mm-5mm - slight / aesthetic concern

5mm-15m - moderate concern

15-25mm - severe

Over 25mm - very severe with stability concerns

36
Q

IF THERE WAS A STEPPED CRACK ON THE CORNER OF A BUILDING, WHAT MIGHT HAVE CAUSED IT?

A

Settlement

Subsidence

Heave

37
Q

WHAT IF THE CRACKS WERE PRESENT ON CONCRETE?

A

Consideration of common concrete defects:

  • Carbonation
  • Chloride attack
  • Silica reaction
  • Issues relating to structural movement
  • Poor design
  • Poor construction
38
Q

WHAT IS CARBONATION IN CONCRETE?

A

CO2 absorbed from outer concrete inwards, can increase tensile and compressive strength, although causes embedded re-bar corrosion (expansive cracking) and degradation of concrete surface

Commences as soon as concrete is exposed to atmosphere, 1-5mm per year dependant on concrete porosity and permeability

Concrete has high pH level (13), carbonation reduces this

Carbonation test - Solution applied, if pink the pH is still high. If clear, the concrete is carbonated

Prevention - Apply protective coating once in a fully hardened state or introduce additives during production

39
Q

WHAT IS CHLORIDE ATTACK?

A

Chloride penetrates concrete surface increasing the risk of reinforcement corrosion

Spalling is caused by expansive corrosion, noted by rust colouring

Causes:
- Use of seawater for concrete mixing process
- Calcium chloride as an additive to inc. setting time
- Introducing aggregates with chlorides

Enter from external environment:
- Seawater exposure
- Use of salt to melt ice
- Presence of chlorides in storage substances

Prevention:
- Inc. reinforcement bar cover
- Coat re-bar in epoxy, cathodic protection or stainless steel clad bar
-

40
Q

WHAT IS SILICA REACTION?

A

Deleterious chemical reaction of aggregate and cement

Produces expansive gel, causing pressure leading to expansion and cracking

Prevent:
- Limit alkali content of the concrete (portland)
- Use of supplementary cementing materials i.e. fly ash / slag

RICS APC Revision (18 decks)

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