Building Pathology Flashcards
What is Licensed Asbestos Work?
This is work that is undertaken on the most friable and therefore high-risk asbestos materials. Examples include work on sprayed asbestos coatings, loose asbestos fibre, asbestos insulation and asbestos insulation boards. It is up to the contractor performing the work on the material to undertake an assessment of risk to determine whether a material is licensable. All works need to be notified to the enforcing authorities by the contractor. This must be done a minimum of 14 days before the commencement of works on site. Licenses are issued by the HSE and are valid for a period of no more than 3 years. All licensed contractors will be subject to site visits by the HSE during the period of the license.
What is non-licensed work?
This classification of work exists to deal with materials where the asbestos fibres are bound in the material. Examples of this are products such as floor tiles, un-weathered asbestos cement and textured decorative coatings where the coating will be removed without deterioration, for example by removing the textured coating together with its backing material such as plasterboard.
What is Notifiable Non-Licensed Work?
This is an intermediate class of work where the deterioration of a low-risk material will occur during the removal process. For example, scraping textured coating from a surface such as a concrete slab would constitute notifiable non-licensed work. Notification is via a digital portal for the purposes of information gathering, and notifications can be submitted immediately before work commences on site.
What are the Housing Eras?
- Tudor – 1485 - 1560
- Georgian – 1714 – 1830s
- Victorian – 1837 – 1901
- Edwardian – 1901 – 1918
- Art Deco – 1920 – 1930s (introduction of lots of light, glazing to doors, steel and concrete more commonly)
- Post-war
- New build
Cold Roof Construction
Insulation located at ceiling level; void or roof slab is insulated from heat loss from below and is therefore at a colder temperature than the room during cold weather. With this form of construction there is a risk of condensation forming within the roof void or on the underside of the slab, so good cross-ventilation is essential. Vapour control layers at ceiling level are essential, but not 100% effective.
Quasi Cold Roof
Roof constructed as above, but without the insulation layer. Risk of condensation forming either on soffits of slab, interstitially or on reverse face of roof deck, i.e. the cold surface.
Warm Roof
Insulation placed on top of the roof deck but beneath the waterproof membrane. Vapour control usually placed under the insulation. This form of roofing has a much reduced risk of condensation as the ceiling or roof void is at a similar temperature to the roof. However, the system prevents heat from infrared radiation from being dissipated.
Inverted Roof
A roof in which the insulation is placed on top of the waterproof membrane. No vapour control is needed. Roof void and or deck are maintained at similar temperature to the room. The insulation protects the membrane from damage but must be anchored down. An inverted roof is also a warm roof.
BS EN for parapet gutters
BS EN 12056-3 - design methods for parapet of valley gutters.
In the UK, for valley and parapet gutters the return period is usually based upon 1.5 times the anticipated life of a building (for example 1.5 x 30 years) since the consequences of a sudden storm would be severe if the gutters overflowed. If a higher degree of protection is needed (for example, for a data centre or archive) the return could be based on 4.5 times the anticipated life of the building or in the alternative the maximum possible intensity.
Rainfall intensities vary according to geographical location, with lowland areas most likely to suffer sudden intensive storms. BS EN 12056-3 provides a series of rainfall intensity maps corresponding to different return periods to enable maximum flows to be calculated; other European countries publish their own data to accord with specific circumstances.
How siphonic drainage works
All siphonic roof drainage systems function in the same way. They comprise a special baffled roof outlet that is connected to a vertical tail pipe. The baffle is designed to prevent air from being drawn into the system so that during rainfall the outlet drain fills above the baffle, cutting off air flow into the pipe. This lack of air, coupled with the downward pull of the water under gravity, creates a vacuum in the tail pipe.
How often should gutters be maintained
At least twice a year and more so if likely to become congested.
Leaf guards can silt up and reduce the flow rates into outlets, in some cases significantly. Under the design codes, the fitting of a leaf guard will mean a 50% reduction in the capacity of the outlet. Leaf guards (or strainers) are usually required for siphonic systems. However, since most siphonic pipes are between 50 and 65mm in diameter they are likely to become congested very quickly with silt, organic matter, construction materials
Calcium Chloride Attack
Until 1977, calcium chloride was routinely added to in-situ and precast concrete as an accelerator, either to enable rapid removal of moulds or to permit concreting in cold weather. Thus, older structures could be at risk of corrosion damage arising from cast-in chlorides coupled with increasing carbonation.
Chlorides can be brought in by vehicles during cold weather from de-icing salts. Affects leads to corrosion and spalling.
Cathodic Protection
Carbonation
Essentially, carbon dioxide in the atmosphere reacts with cement hydrates to form calcium carbonate. The process lowers the alkalinity of the concrete, which then leads to the depassivation of the steel reinforcement. Corrosion does not necessarily follow, but depassified steel is certainly at risk of corrosion given exposure to moisture and oxygen.
Carbonation spreads from the outside of the concrete inwards, so good quality, well-compacted concrete carbonates at a much slower rate than poor quality materials. If poor compaction and strength (perhaps caused by too high a water:cement ratio) is coupled with misplaced reinforcement with little cover, the corrosion risk is high.
Corrosion caused by carbonation will be accelerated in damp conditions, while in dry areas, the rate of carbonation will be higher. Carbonation also liberates a certain number of chloride ions that may have been incorporated in the original mix and would otherwise be chemically bound in. So, there is a risk that electrical conductivity in the concrete could increase, with the consequent increase in corrosion currents and therefore corrosion.
In certain cases carbon dioxide released from vehicle exhausts can lead to greater carbonation rates in concrete than would be experienced in well-ventilated conditions. Such problems can occur in crowded, poorly-ventilated city centre car parks where vehicles are left running for longer periods.
Issues with Aluminium Composite Panels?
Aluminium composite material (ACM) cladding is a versatile product that has been around since the early 1970s and was used predominantly in low-rise constructions, typically at entrances and lobbies.
ACM is essentially 2 thin skins of aluminium or other metal, bonded to a plastic core to form a relatively rigid sheet some 3–4mm thick. The sheet can be folded and shaped easily to form a cladding panel. The basic core material can be highly flammable, however, so it must be used with extreme caution, particularly on high-rise properties.
The insulation and cavity barriers behind it must also be selected and installed carefully to conform to the appropriate parts of Approved Document B. The system as a whole – the cladding, insulation, fixings and cavity barriers – must also comply with the requirements of BS 8414. The Department for Communities and Local Government’s guidance notes provide the latest information.
Stick System
Stick construction is the traditional form of curtain walling, comprising a grid of mullions and transoms into which various types of glass and/or insulated panels can be fitted. The systems are usually fairly low cost, using extruded components supplied by the system manufacturer. Mullions are usually assembled first, with transoms then fitted in-situ.
A variety of jointing systems are employed but most stick systems have some form of stub connection between individual lengths or transoms. Mullions are usually fixed back to the structure at floor levels, although longer spans are possible according to the section properties of the component.
Aluminium is the usual material for the framework, although some older buildings experimented with steel. Most of the grid assembly work is done on site. This permits some measure of dimensional adjustment and tolerance, but it is highly workmanship-sensitive and relies on accurate cutting of components and the correct use of sealants at joints.
Assembly on site is fraught with risk as many systems are superficially similar so that a contractor who is familiar with one system may omit crucial components such as seals at junctions when assembling components provided by another manufacturer. (Weatherproofing problems in modern glazing systems, CIOB, 1992) Similarly, if shop drawings are hard to read (perhaps in a different language) or do not detail items such as drainage or ventilation slots, there is a risk that these items are neglected or installed incorrectly.
Unitised Cladding System
Unitised systems comprise narrow-width, storey-height units of aluminium framework containing glazed and/or opaque insulated panels. The entire system is pre-assembled under factory-controlled conditions, thus avoiding some of the problems of assembly encountered on site.
The unitised panels are usually craned into position, with pre-positioned brackets attached to the floor slab or the structural frame. Modern installation techniques increase the speed of erection and often minimise the requirement for scaffolding.
Unitised systems do have higher direct costs but nowadays the curtain walling to most prestige buildings is of this type.
Panelised System
Like unitised systems, panellised curtain walling is constructed in the factory to improve quality control and speed of erection. However, the systems comprise large prefabricated panels of bay width and storey height, which are connected back to the primary structural columns or to the floor slabs. Panels may be of precast concrete or comprise a structural steel framework and are often clad with a variety of stone, metal and masonry cladding materials.
The advantage of these systems is improved adherence to specification as a consequence of factory prefabrication, allowing improved control of quality and rapid installation with the minimum number of site sealed joints. Panellised systems are less common and more expensive than unitised construction.
Panelised facade systems are similar to unitised ones, but the prefabricated modules are generally much larger and can incorporate different materials and components such as metal panels, brick and windows
What is SBR Primer?
SBR primer is a latex-based liquid bonding agent that is applied to a variety of substrates before the addition of tiles, screeds, or plasters. Its primary function is to improve adhesion between surfaces ensuring that subsequent layers bond correctly and last longer.
SikaBond SBR+ has the advantage over PVA bonding aids in that it is not adversely affected in wet conditions, has excellent resistance to water and water vapour, and has improved frost resistance, therefore making it ideal for exterior use. SikaBond SBR+ has a reduced water to cement ratio for equivalent workability, making it easier to spread and can be applied in much thinner sections. SikaBond SBR+ also has a high level of resistance to salt permeation, a reduced surface dusting of concrete and a greatly improved resistance to many chemicals.
Sand & Cement Render vs Lime
Sand and cement rendering, whether used as a finish coat in its own right or as a background to tiling or other finishes, can be problematic for several reasons. The choice of mix will influence the performance of the coating and indeed the substrate to which it is attached.
For example, a dense cement rich render absorbs little water, but it is also inflexible. When the inevitable cracks occur, water may penetrate behind the render to promote deterioration by frost action, chemical attack or dampness. By contrast, a weaker, more flexible render (such as a mix of 1:1:6 cement:lime:sand) can absorb more moisture and will crack less. Such materials are more able to promote drying by evaporation so that damp penetration and resultant chemical or frost problems are less prevalent.
With a cement rich render, any moisture that does penetrate to the interface between the render and the background will take longer to dry out. Certain masonry, such as Fletton or common brickwork, contains high levels of soluble sulphates. In persistently damp conditions, the sulphates react with the alumina in Portland cement to form ettringite: a process which causes expansion, disintegration and loss of strength, with the render often developing a series of parallel cracks along bed joint lines.
Cement render shrinks on drying and imparts a force upon the background. The adhesion of the render to the background must be good enough to overcome the shrinkage force otherwise delamination will occur. When render is applied to smooth dense surfaces, such as concrete and certain types of well-burnt brick, it is essential to provide an additional mechanical key otherwise adhesion failure is likely.
What are the two types of Formaldehyde resin?
urea formaldehyde (UF) and phenol formaldehyde (PF). Products made of UF can release formaldehyde gas, while products made of PF generally emit lower levels of the gas.
Typically, sources of formaldehyde include:
building materials
smoking
household products (e.g. to add permanent press qualities to clothing and curtains)
unvented fuel burning appliances
preservatives in paints and coatings
building adhesives
wood particle boards, such as chipboard, oriented strand board, hardboard and medium density fibreboard (in these instances formaldehyde resins are utilised in the adhesives) and
plywoods (generally internal varieties).
Vermiculite
Vermiculite is a naturally occurring mineral from a group known as hydrated laminar magnesium silicates. When heated, flakes of the material expand by as much as 30 times to form concertina-like particles – a process known as exfoliation.
Vermiculite applications
Vermiculite is used in thousands of applications from light weight concrete, fire protection construction materials, intumescent applications, potting soils, texturisers in paints and coatings, and as nano-composites for films, coatings and barrier applications. Building applications include thermal insulation products, sprayed fire protection, thermal and sound insulation and insulating boards.
In the construction industry, uses include:
fire protection
fire rated wall boards, gypsum and vermiculite cores to fire doors
thermal insulation materials (largely before the advent of mineral wool materials)
spray applied fire protection, thermal insulation and sound insulation
lightweight concrete
bio-remediation for contaminated soil
packaging materials and
oil spill materials.
Risks to vermiculite
Vermiculite can contain small fibres not unlike asbestos, but scientific investigations have failed to establish any particular link with cancer as a result of the inhalation. However, the material can produce silica dust, prolonged exposure to which can lead to the serious lung condition silicosis. (See Health effects.) The general conclusion in the UK is that the material is safe to use, although normal and sensible handling precautions should be employed to control nuisance dust, exposure to the skin and eyes.
Commercially available vermiculites are virtually free of any asbestos or contain only insignificant amounts similar to other products that are naturally occurring, but unreasonable doubts and reservations have persisted. Caution should be exercised when dealing with older materials that might have originated from a contaminated source and when handling it is necessary to take normal precautions to avoid the inhalation of nuisance dust.
