World‘s number 1 brick manfacturer

• Undertook a global expansion in 1986 with the acquisition of several well-known brands
• Have over 230 producing plants across 27 countries
• Operating in the US, Canada and India as well as Europe
• 11,800+ employees
• €1.8 billion annual turnover
• A wide range of clay building solutions

Facing bricks (facade)
– No. 1 in Europe, Co-Leader in US
– 54 factories

Roof systems
– 39 factories worldwide

Pavers
– 6 clay and 21 concrete factories

Clay Blocks (walls)
– 79 factories worldwide

The RICS study compared brick and other cladding materials, such as weatherboard, rendered blockwork, PVC, stone glazing, fibre cement board and found that brick is significantly cheaper.

The cost is usually under £60 per metre square which equates to about 1/3 of the cost of stonework, 2/3 less than timber weatherboarding and about 8 times cheaper than curtain wall and glazing.

Brick has excellent sound insulation properties, as it is a solid and permanent material.

It is also a very low maintenance material with an extremely high fire resistance

The thermal mass properties help to contribute to healthy, comfortable living conditions, which provides a massive range of applications and aesthetic flexibility.

It is important to recognise that all building materials are subject to movement.

Clay bricks are manufactured in different ways (so suit the characteristics of the raw material); this in turn leads to different technical characteristics, e.g. strength, water absorption, but these do not affect the principles of movement joint provision.

Similarly, although there are different categories of mortar (with cement rich mixes being more rigid and less forgiving) which can influence masonry movement, nevertheless sensible provision of movement joints will avoid any issues.

Clay Brick Characteristics

• Manufacturing Methods
  • Handmade
  • Machine Moulded
  • Extruded
• Technical and Aesthetic Properties
• Mortar

There are three basic elements to consider with clay bricks – the expansion and contraction of material as temperature rises and falls, the effect of wetting and drying (reversible) but there is a third element to be considered with clay units, namely a longer term moisture expansion.

•  Thermal Movement   –  reversible  ( +/– )
•  Moisture Movement  –  reversible  ( +/– )
•  Moisture Movement  –  irreversible  ( + )

Looking at these individually, every material has a co-efficient of expansion – this varies with different clay types, although the difference between ‘5’ and ‘8’ x 10-6 is insignificant.

The amount of movement will vary depending on the orientation of elevations – a South facing wall will experience a higher temperature profile than the opposite side.

The thickness of walls, and the type of wall ties and any reinforcement, creating restraint, will also have an influence.

Thermal Movement

•  Co-efficient of Expansion
•  5 – 8 x 10-6 per degree C
•  Effect of orientation and restraint

Moisture Movement  –  reversible

•  + 0.02%
•  negligible (0.2mm/ metre)

As stated above, the wetting and drying process will have an affect on the overall movement, although this is negligible.

Moisture Movement  –  irreversible

•  Moisture reaction with fired clay – ‘adsorption’
•  Longer term ‘creep’ (0.02 – 0.07%)

The third element referred to involves a longer term creep, following a reaction at a molecular level as the bricks are exposed to the ambient atmosphere; the range is related to different clay characteristics.

Long-term Moisture Expansion…

•  Accelerated steam expansion tests…
•  Correlation with natural exposure expansion
•  Allows prediction (50 years?) of categories (‘low’ ‘medium’ ‘high’)

To predict the long-term effect, steam expansion tests were developed many years ago (in different countries) – saturated steam at atmospheric pressure –  and results over a five year period, while not completely reliable for a 50 year or longer extrapolation, are sufficiently proven to allow bricks to be categorized into three broad expansion bands.

Overall Movement  –  calculation

•  Thermal :  1000mm x (6 x 10-6) x 45oC   = 0.27mm  (say 0.03%)
•  Reversible Moisture : 0.02%
•  Irreversible Moisture : 0.07% (worst case)
•  Total Movement : 0.12% (1.2mm per metre run)
•  Worst case guideline  –  1mm of movement per metre

It is not the case however that all three elements will be acting together – a high thermal movement would not occur in rain conditions – but nevertheless it is useful to offer a guideline of 1mm/ metre for the provision of movement joints.

To consider the effect of all three elements, a calculation is helpful.  For a metre length, with an average co-efficient of expansion, and the likely temperature rise (experienced by a southerly facing wall), the thermal contribution will be approx. 0.03%.

We have established that the reversible (wetting and drying) effect is in the order of 0.02%, and taking the worst case irreversible moisture expansion, we arrive at a total theoretical movement of just over a millimetre per metre run of brickwork.

Reference Documents

•  BS 5628 Part 3 : 2005 (withdrawn 2010…)
•  Max. joint spacing  –  15 metres (to avoid cracking due to thermal contraction)
•  Replacement document  –  BSI PD 6697 : 2010
•  General established rule  –  10 – 12 metres centres
•  Additional provision for lightly restrained/ freestanding walls

The Code of practice for masonry, BS5628 was withdrawn in 2010, but Part 3 referred to a maximum spacing of joints at 15 metres (to avoid cracking due to thermal contraction).

The Industry advice is that vertical joints should be considered at maximum 10 – 12 metres (allowing for a reasonable joint size) but for specific elements, including parapets and free-standing walls, a doubling up of joints should be considered. (These would be classified as ‘unrestrained’ or ‘lightly restrained unreinforced’ walls, and PD6697 suggests 1mm/m but to consider the compressibility of the filler, an allowance of 30% should be added to the joint width – balanced of course by more frequent joints).