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