RIBA Core Curriculum
- Design, construction and technology
- 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
World‘s number 1 brick manfacturer
Facing bricks (facade)
– No. 1 in Europe, Co-Leader in US
– 54 factories
– 39 factories worldwide
– 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.
Why is it that we don’t see movement joints in historic buildings?
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 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, diving pas long estate walls that although no vertical joints are visible, the walls have nevertheless moved, possibly by curving where the mortar has accomodated the movement.
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
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.
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.
Moisture Movement – reversible
As stated above, the wetting and drying process will have an affect on the overall movement, although this is negligible.
Moisture Movement – irreversible
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…
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
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.
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).
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.