04 Walls Flashcards
What are the dimensions of a brick?
215mm x 102.5mm x 65mm
Name some different types of brick bond.
- English bond
- Flemmish bond
- Header bond
- Stretcher bond
- English garden wall bond
- Flemmish garden wall bond
How does English bond differ from Flemish bond?
- English Bond - alternate rows of headers and stretchers (one of the strongest bonds but requires more facing bricks)
- Flemish Bond - alternate headers and stretchers (not as strong as English bond but uses less facing bricks and is considered to be aesthetically superior)
What is the difference between a common, facing and engineering brick?
- Common brick - basic clay brick, no attempt at colour/texture control or special surface treatment
- Facing brick - more attractive, sides more accurately finished and smoothed, colours more uniform
- Engineering brick - used where strength, low water porosity or acid (flue gas) resistance is needed
What is the function of mortar in brick/block walls?
The material that binds bricks/blocks together, helping to distribute the load through a wall and seals the bricks/blocks against water ingress
How is mortar made?
Made by mixing a fine aggregate (usually sand) and a binding agent (traditionally lime, nowadays cement) with water
How is mortar expressed in terms of its component parts?
Expressed as either a cement/sand ratio (i.e. 1:3) or a cement/lime/sand ration (i.e. 1:1:6)
Explain the purpose of using a plasticiser in a mortar mix?
Lime or a liquid plasticiser is often added to the mortar to allow the mix to flow better, thus increasing workability (a 1:1:6 mix is the same strength as a 1:3 mix without lime)
What are the implications of using a weaker mortar mix in constructing a wall?
A weaker mix (proportionally less cement):
- More flexible - able to resist the stresses imposed by movement
- If cracking occurs, it will tend to happen at the weaker mortar joints, allowing for an easier/cheaper repair than repairing/replacing the bricks
- Too weak and the mortar will become porous and may crush under high compression forces
What are the implications of using a stronger mortar mix in constructing a wall?
- Increased strength and durability
- Absorb less water and are more resistant to frost attack
- Reduced ability to accommodate movement - tendency to shrink and crack, allowing water into the wall
- Reduced workability
Why may using a strong mortar mix be detrimental when repointing an older building?
A strong mortar can lead to damage in the brick/stone itself, as it fails to perform as a sacrificial item or fails to allow water to evaporate adequately
What factors would you consider when specifying the type of mortar to be used?
- Structural requirements
- Ability to accommodate movement
- Resistance to frost during construction
- Resistance to rain penetration
- Better adhesion
- Characteristics of the brick
What guidance is available when specifying mortar?
BS 998-2 (Table NA.1, showing 4 categories with varying attributes)
What is pointing?
Act or process of repairing or finishing joints in brickwork, masonry etc. with mortar
What is a DPC?
Damp Proof Course - impermeable layer of material to prevent rising damp, most often polyethylene or bitumen-polymer
When did damp proof courses become compulsory in buildings?
Mandatory in all British buildings since the Public Health Act in 1875
When did damp proof membranes become compulsory in buildings?
Made compulsory by the National Building Regulations in 1965
Name some different materials that have been used for DPCs and DPMs over the years.
Early DPCs included (many become brittle with age and fail due to building movement):
- Tar and sand
- Hessian soaked in tar
- Lead
- Copper
- Slate
- Two/three courses of engineering bricks
What are the main requirements for DPCs and DPMs in relation to the building regulations?
- Part C requires the DPC to sit at least 150mm above ground level
- Part C requires DPMs to be continuous with the DPC on the inner leaf
When were cavity walls introduced?
- Introduced by the Victorians as early as 1850
- More commonly introduced in the 1920s
What is the purpose of cavity walls?
- Prevents water reaching the internal skin
- Improves thermal efficiency - air is a good insulator and addition of cavity wall insulation improves this further
Describe the typical elements that make up a cavity wall.
- Outer leaf (i.e. facing bricks)
- Cavity
- Insulation board
- Inner leaf (i.e. aerated blocks)
- Wall ties
- DPC (on each leaf, 150mm minimum from ground level)
- Backfill (weak concrete mix below ground)
Where would the partial fill insulation be placed in the cavity wall?
Held against the inside leaf by retaining washers clipped on the walls ties
Why would you backfill a cavity?
- Prevents the inner and outer leaf being squeezed together when trenches are backfilled
- Must stay well below DPC level and be struck away from the internal leaf so water falls to the outer leaf
How has the material from which wall ties are made changed over the years?
- Cast or wrought iron first used until approximately the 1930s
- Galvanised steel (coated in zinc to protect the steel electrochemically, slowing the corrosion process) used thereafter, although minimum thickness of zinc cover was reduced in 1968 (but later increased again in 1981)
- Part A now requires stainless steel (ferrous alloy containing at least 10% chromium, forming a ‘self-healing’ impermeable layer of chromium oxide on the surface of the steel thus preventing the formation of rust) to be used
- Plastic ties are also now commonly used
What spacing would you have for cavity wall ties in a cavity wall?
- Part A requires a 900mm horizontal spacing and 450mm vertical spacing, or no less than 2.5 ties/m²
- Extra ties are required around openings (300mm vertically, within 225mm from the vertical edges)
In a brick/block cavity wall, how are window openings dealt with in terms of closing the cavity and preventing water penetration?
- The Head - modern construction uses steel ‘Catnic’ lintels with an insulated core, shaped to incorporate a cavity tray which prevents damp penetration and cold bridging
- The Jambs - in modern construction, uPVC cavity closers with an insulated core are installed, preventing both cold bridging and damp penetration, whilst allowing for a quick and easy installation
- The Sill - insulated uPVC cavity closers are now often used
What materials are available for window frame construction?
- Timber
- Aluminium
- uPVC
- Steel
What are mullions and what are transoms?
- Mullion - a vertical bar/member dividing a window
- Transom - a horizontal bar/member dividing a window
What would you consider when specifying windows?
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Name some different types of glass used in glazing systems?
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How can masonry be extended?
- Metal connector plate (or ‘wall starter system’) bolted to the existing wall and metal wall ties tie in the new wall at appropriate intervals - advantageous as it is quick, easy and best used if the old brickwork is of a different size/colour to the new
- Tooth-in new brick work with the existing brickwork - consider colour matching (may need to try and conceal the join behind a rainwater pipe or set the new wall back from the face of the existing to provide a shadow gap)
Explain the term ‘corbeling’.
A corbel is a bracket projecting from a wall to support a structure above - combining several corbels one on top of another is described as ‘corbelling’
How are modern brick slips applied to walls?
Applied to surfaces in one of three ways:
- Bonded to a concrete panel and then pointed
- Mechanically clipped and then pointed
- Glued onto an insulated backing panel and then pointed
L-shaped slips are available for corners/returns
What different types of plaster and render are there?
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What is curtain walling?
A weather-proof, non-loadbearing enclosure of windows or metal panels in a light metal framework which is fixed back to the structure of a building, usually at intermediate floor levels
What types of curtain walling system exist?
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How are curtain walling systems made watertight?
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What is rain screen cladding and how does it work?
A rainscreen is an exterior wall detail where the cladding is attached to the main structure with a grid of simple metal framing or vertical timber battens, allowing space for a ventilated and drained cavity behind, with provision for insulation to be attached to the substructure
How is composite metal cladding fixed to a steel frame?
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What is a diaphragm wall and how does it work?
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What materials are typically used for internal partitioning?
- Timber framed
- Metal framed
- Blockwork
- Brickwork
