Building Pathology (Level 1) Flashcards
- What typical building defects might you expect to see on a Victorian residential property?
Main defects included:
differential settlement of part basements in terraces;
lack of lateral support from one terraced house to another (the ‘book end’ effect);
blocked air vents to ground floors, causing dry rot;
removal of chimney breasts but not the stack;
heave or subsidence of shallow foundations;
rot and creep in timber beams;
blown plaster;
lead water pipes;
party walls unbonded to external wall junctions;
failing brick arches;
wall tie failure (particularly in black ash mortar);
differing loads caused by a change of roofing material (usually introduction of cement tiles);
unsuitable mortar mixes used for repointing (mainly pre-1820s);
water ingress through solid masonry walls and exposed hollow walls (the trend to lay patios that raise ground levels is a particular hazard);
water ingress through corbels and copings (mainly poorly maintained pointing);
condensation problems, for example, single-skin privy and the coal-house converted to a bathroom (1940-60s) without increased insulation;
double-height bays can rotate on shallow footings, especially if water mains laid below leak and cause local elasticity of the soil;
the use of chimneys as gas appliance flues without using a liner;
poor water tank installations and pipes freezing in uninsulated roofs; and
earthing to metal pipes above ground that have plastic replacements underground.
Particular to converted industrial buildings were:
deterioration of clinker in filler joist mass concrete floor systems;
collapse of mass concrete floors after fires and flooding (most floors fail from the top, with lower floors unable to support the weight of the floor above falling on them); and
corrosion of metal components in encased mass concrete.
Defects of the period
Defective wall ties and tying in.
Defective slates and nail sickness.
Sagging roof timbers.
Blown plaster.
Defects related to Services, such as lead pipes and electrical installations.
- What typical building defects might you expect to see on a 1980’s industrial unit?
- How would you identify condensation in a property?
Wall has a misty surface
Stains or streaks of water running down the wall, particularly in bathrooms and below windows
Damp patches with no definite edges
Dampness behind cupboards or inside wardrobes where air circulation is restricted
Patches of mould growth
Temperature / Relative humidity above x% / cold surfaces - dew point
- If a property was suffering from dry rot, what might you expect to see?
Cuboidal cracking and darkening of the wood
Fruiting bodies
20 - 35% dampness
Optimum growth rate at 22c (0c - 26c)
Will die if exposed for short periods to temps above 40c
List the main types of beetles which attack timber within buildings in the UK
Death watch beetle - Emergence holes and tunnels are circular, 3mm to 4mm in diameter, and extensive mainly in the direction of the grain of the wood. The beetles produce cream-coloured, disc-shaped pellets (bore dust).
Common furniture beetle: woodworm - Infestation is usually detected by emergence holes of up to 2mm in diameter. Active infestation produces fresh frass (bore dust), which is cream coloured or the colour of freshly cut wood.
Termites - They fall into two distinct categories:
Subterranean termites are the most widespread type and are responsible for the most damage. They nest outdoors and travel in mud tunnels, which they build over surfaces to reach wood. Houses need careful design to prevent this tunnel building or else the surrounding soil needs to be poisoned.
Dry wood termites never enter the ground. They live in dry wood only; the infestation is started by winged forms laying eggs in cracks and joints of structural timber and furniture. An intact skin is left on the surface, so attacks can be severe but not noticed until collapse occurs. Only preservation techniques will protect wood. Some species of timber are naturally resistant, but the resistance varies in different countries according to the species of termite that lives there.
Explain your understanding of nail fatigue?
The copper or iron nails corrode and cause individual tiles or slates to slip.
What is concrete carbonation?
Carbon dioxide from the atmosphere penetrates into concrete and reacted with calcium hydroxide to form calcium carbonate then this process is called carbonation. Results in the corrosion of rebars.
Explain the cause of concrete carbonation.
When the carbon dioxide from the atmosphere penetrates into concrete and reacted with calcium hydroxide to form calcium carbonate then this process is called carbonation. In general concrete with high alkali content form a protective layer around the reinforcement. But when the carbon dioxide changes into dilute carbonic acid it reduces the alkalinity as a result the corrosion of reinforcement takes place.
Carbonated concrete has a pH value of 8.3 while the passivation of steel starts at a pH value of 9.5. The depth of Carbonation in good dense concrete is about 3 mm at an early stage and may increase to 6–10 mm after 30–40 years. Poor concrete may have a depth of Carbonation of 50 mm after say 6–8 years. The rate of Carbonation depends on
Time
Depth of cover
Concrete density
Cement content
Water-to-cement ratio
The presence of cracks
The depth of carbonation is determined using the solution of phenolphthalein in diluted alcohol. When the solution is applied the Non – carbonation zones becomes pink in color and remaining uncolored portion is termed as carbon affected zone
Explain the testing procedure when testing for concrete carbonation
Testing for carbonation in ordinary Portland cement (OPC) concrete is relatively straightforward and can be undertaken on site or, if greater accuracy is needed, in the laboratory using petrographic analysis.
Site tests usually involve exposing a fresh sample of broken concrete and applying an indicator solution of 1g phenolphthalein in 50g alcohol diluted in 100ml of deionised water. The indicator solution will turn pink on contact with suitably alkaline (uncarbonated) concrete and remain clear on carbonated concrete. The depth of penetration can then be measured. Care is needed, however, that the sample is not distorted or contaminated. It is usual to drill two holes 10–15mm apart and to break the concrete between them to expose a fresh surface. As an alternative a core can be split laterally to provide a suitable surface. Measurement of the core itself (i.e. an unsplit core), a sawn edge or a corner knocked off a column is likely to produce a misleading result.
What is a deleterious material – give me some examples?
Materials or building techniques that are dangerous to health, environmentally unfriendly, tend to fail in practice or can be susceptible to change over the lifetime of the material.
The isurv Deleterious materials sections look at materials that:
are harmful to health
are harmful to safety
are harmful to the environment
are not suitable for their intended purpose or
pose a risk where they have been used.
Concrete - Calcium chloride (admixture/de-icing salts/marine aggregates/sea water) leading to corrosion of steel reinforcement.
Concrete - Chlorides
Concrete - High alumina cement (HAC)
Asbestos
Glass - Nickel sulphides (chemical contaminants that can occur during the manufacture of glass)
Wood - Wood preservatives (Wood preservatives comprise an active ingredient and a carrier system. There are a great many types of active ingredients available, some highly toxic or harmful to the environment)
Lead
What are the problems associated with high alumina cement?
HAC could lose a substantial part of its strength and durability with time.
HAC can be seriously affected by contact with other materials such as gypsum, and in damp conditions a condition known as alkaline hydrolysis can have a profound impact on strength
Explain how you would test a masonry wall for the possible presence of damp
Moisture meter - resistance via pins or probes /capacitance meter - below surface
Carbide testing
Thermography
How would you differentiate between the different types of damp likely to be present in a property?
Penetrating
rising
Condensation
Leaks (pipework/services)
Give some examples of the possible causes of penetrating damp
Leaking rainwater goods
Overflowing gutter
Roof leak
Bridged DPC
Defective flashings
What are the limitations when using a damp meter?
Damp meters calibrated for measuring moisture content in timber.
Can obtain false positive readings due to the presence of salts or foil-backed plasterboard.
Pins typically only measure shallow depth and can leave marks or damage plaster.
