Products > Brick

RIBA Core Curriculum
- Design, construction and technology

Knowledge level
- General Awareness

This CPD looks at situations where problems have arisen from movement in brickwork. The course also covers the basic British Standard requirements for designing as well as how to recognise issues and minimise the risk of damage.

In this section
- Why is it that we don’t see movement joints in historic buildings?
- Thermal and Moisture movement and calculations
- Examples of movement in brickwork

            
                    
Navigate through each step of the CPD using the left and right arrows to review the content. At the end of each section are some questions, these are required if you wish to obtain a certificate upon completing the course.                     
                                     
            
    

Who are Wienerberger?

Paver_CPD_Family Tree

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
Movement_5
Typical Core Range Usage: Monolithic

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

Why Brick?

Movement_6
Movement_7
Movement_8
Movement_9

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.

 

Why is it that we don’t see movement joints in historic buildings?

Movement_11

The method of construction was rather different centuries ago, when walls were thicker, offering more self restraint.

Movement did occur of course, and in some cases, cracking would have been evident.

The type of mortar historically though was not of the strong cement based compound we use today – lime and sand was used, which has a self healing effect following movement.

You may have noticed, driving past long estate walls that although no vertical joints are visible, the walls have nevertheless moved, possibly by curving where the mortar has accommodated the movement.

Movement did occur of course, and in some cases, cracking would have been evident.

The type of mortar historically though was not of the strong cement based compound we use today – lime and sand was used, which has a self healing effect following movement.

You may have noticed, driving past long estate walls that although no vertical joints are visible, the walls have nevertheless moved, possibly by curving where the mortar has accommodated the movement.

Here we see a long section of garden walling… but again, cracking has occurred.
Here we see a long section of garden walling… but again, cracking has occurred.

Movement in Brickwork

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

This illustrates a major structural problem, but we are not concerned in this presentation with the causes of settlement or foundation issues – we are looking at the material characteristics of clay facing bricks and the points to be considered in the design and at the specification stage.
This illustrates a major structural problem, but we are not concerned in this presentation with the causes of settlement or foundation issues – we are looking at the material characteristics of clay facing bricks and the points to be considered in the design and at the specification stage.

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.

Movement in Brickwork

Movement_68
We should allow for movement horizontally (and walls can move along the damp proof course if not bedded properly)
Movement_16
Here we see the effect of the main brickwork literally sliding along the dpc.
Movement_69
Vertical movement also needs to be considered.

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).

Ask a Question about this CPD




CPD Q&A

You’ve reached the end of the CPD. To make sure you’ve taken on board the key learnings of this course, please fill out the quick multiple choice Q&A below. This will certify that you have completed the CPD and provide you with an email certificate, which, if the course is accredited, you can share with RIBA.

Question

Historically what was mortar made from?

CORRECT

Well done!
You can move on to the
next CPD question.

INCORRECT

Whoops!
You might want to reread our
course content.

arrow_upward
RECAP

Question

Which of these is not a consideration when working with clay bricks?

CORRECT

Well done!
You can move on to the
next CPD question.

INCORRECT

Whoops!
You might want to reread our
course content.

arrow_upward
RECAP

Question

Industry advice is that vertical joints should be considered at maximum of what distance?

CORRECT

Well done!
You can move on to the
next CPD question.

INCORRECT

Whoops!
You might want to reread our
course content.

arrow_upward
RECAP
arrow_upward
BACK TO TOP