Floor and wall construction

Question 1

Name some different types of floor construction.

Answer 1

Suspended timber
Suspended block and beam
Solid concrete slab
Composite floor deck
Ribbed and waffle slabs

Question 2

What is a composite floor deck?

Answer 2

Profiled steel floor deck (acting as permanent shuttering) with in-situ concrete cast over the deck

Question 3

What is the function of a floor screed?

Answer 3

Provides a finishing layer onto existing structural base
Not intended to be wearing courses, so should be protected with another material such as carpet, vinyl etc.
Can also be used to create falls in the floor, e.g. in wet rooms

Question 4

What are the dimensions of a brick?

Answer 4

215mm x 102.5mm x 65mm

Question 5

Name some different types of brick bond.

Answer 5

English bond
Flemmish bond
Header bond
Stretcher bond
English garden wall bond
Flemmish garden wall bond

Question 6

How does English bond differ from Flemish bond?

Answer 6

1English Bond - alternate rows of headers and stretchers (one of the strongest bonds but requires more facing bricks)
2Flemish Bond - alternate headers and stretchers (not as strong as English bond but uses less facing bricks and is considered to be aesthetically superior)

Question 7

What is the difference between a common, facing and engineering brick?

Answer 7

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

Question 8

What is the function of mortar in brick/block walls?

Answer 8

The material that binds bricks/blocks together, helping to distribute the load through a wall and seals the bricks/blocks against water ingress

Question 9

How is mortar made?

Answer 9

Made by mixing a fine aggregate (usually sand) and a binding agent (traditionally lime, nowadays cement) with water

Question 10

How is mortar expressed in terms of its component parts?

Answer 10

Expressed as either a cement/sand ratio (i.e. 1:3) or a cement/lime/sand ration (i.e. 1:1:6)

Question 11

Explain the purpose of using a plasticiser in a mortar mix?

Answer 11

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)

Question 12

What are the implications of using a weaker mortar mix in constructing a wall?

Answer 12

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

Question 13

What are the implications of using a stronger mortar mix in constructing a wall?

Answer 13

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

Question 14

Why may using a strong mortar mix be detrimental when repointing an older building?

Answer 14

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

Question 15

What factors would you consider when specifying the type of mortar to be used?

Answer 15

Structural requirements
Ability to accommodate movement
Resistance to frost during construction
Resistance to rain penetration
Better adhesion
Characteristics of the brick

Question 16

What guidance is available when specifying mortar?

Answer 16

BS 998-2 (Table NA.1, showing 4 categories with varying attributes)

Question 17

What is pointing?

Answer 17

Act or process of repairing or finishing joints in brickwork, masonry etc. with mortar

Question 18

What is a DPC?

Answer 18

Damp Proof Course - impermeable layer of material to prevent rising damp, most often polyethylene or bitumen-polymer

Question 19

When did damp proof courses become compulsory in buildings?

Answer 19

Mandatory in all British buildings since the Public Health Act in 1875

Question 20

When did damp proof membranes become compulsory in buildings?

Answer 20

Made compulsory by the National Building Regulations in 1965

Question 21

Name some different materials that have been used for DPCs and DPMs over the years.

Answer 21

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

Question 22

What are the main requirements for DPCs and DPMs in relation to the building regulations?

Answer 22

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

Question 23

When were cavity walls introduced?

Answer 23

Introduced by the Victorians as early as 1850

More commonly introduced in the 1920s

Question 24

What is the purpose of cavity walls?

Answer 24

Prevents water reaching the internal skin

Improves thermal efficiency - air is a good insulator and addition of cavity wall insulation improves this further

Question 25

Describe the typical elements that make up a cavity wall.

Answer 25

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)

Question 26

Where would the partial fill insulation be placed in the cavity wall?

Answer 26

Held against the inside leaf by retaining washers clipped on the walls ties

Question 27

Why would you backfill a cavity?

Answer 27

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

Question 28

How has the material from which wall ties are made changed over the years?

Answer 28

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

Question 29

What spacing would you have for cavity wall ties in a cavity wall?

Answer 29

1Part A requires a 900mm horizontal spacing and 450mm vertical spacing, or no less than 2.5 ties/m²
2Extra ties are required around openings (300mm vertically, within 225mm from the vertical edges)

Question 30

In a brick/block cavity wall, how are window openings dealt with in terms of closing the cavity and preventing water penetration?

Answer 30

1. 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
2. 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
3. The Sill - insulated uPVC cavity closers are now often used

Question 31

What materials are available for window frame construction?

Answer 31

Timber
Aluminium
uPVC
Steel

Question 32

What are mullions and what are transoms?

Answer 32

Mullion - a vertical bar/member dividing a window

Transom - a horizontal bar/member dividing a window

Question 33

What would you consider when specifying windows?

Answer 33

I would consider the buildings location, is there a lintel above the window.

Question 34

How can masonry be extended?

Answer 34

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)

Question 35

How are modern brick slips applied to walls?

Answer 35

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

Question 36

What is curtain walling?

Answer 36

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

Question 37

What is rain screen cladding and how does it work?

Answer 37

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

Question 38

What materials are typically used for internal partitioning?

Answer 38

Timber framed
Metal framed
Blockwork
Brickwork