CPD 12 2022: Movement in brickwork 

This CPD sponsored by Vandersanden explores the benefits of specifying clay brick, alongside the types and causes of movement in brickwork and how to design to accommodate movement

Brick is highly durable, fire resistant and cost efficient compared with many other facade material

There are many advantages to specifying clay brick. It is a highly durable and frost-resistant material, and it adds to the thermal mass of a building. It is also non-combustible, classed as A1 under the European classification system for reaction to fire set out in BS EN 13501-1:2018 and is cost-efficient in comparison with many other facade materials. 

Clay is sourced from a natural and abundant resource, and it is reusable and recyclable at the end of its lifespan, which is in excess of 100 years. There are examples of Roman brickwork still standing over 2,000 years old. Bricks are available in a wide range of colours and textures to suit individual taste and various styles of building, and they offer a low-maintenance finish.

Learning objectives  

This CPD aims to enable you to: 

  • Understand why clay brick is a sustainable material   
  • Gain awareness of the types and causes of movement  
  • Understand where vertical and horizontal movement joints are required in brickwork 
  • Acquire knowledge of industry standards and relevant regulations.  

Brick as a sustainable product 

Clay, the main raw material for manufacturing brick, is quarried and is also taken from earth-moving activities and infrastructure projects such as roadbuilding, as a by-product.  

Water is used in the manufacturing process, with collected rainwater used where possible to supplement the clean water used. Many brick manufacturers use heat recuperation during the manufacturing process. Heat from the kilns is reused in driers, where bricks are dried before firing. 

Where lime mortar is used, it is possible to deconstruct brickwork and reuse the bricks in new construction. Where cement mortar is used, it is more difficult to remove mortar from the bricks, but they can be recycled by crushing for use as infilling material. It is advised to be cautious with reclaimed bricks, as there may be no evidence to prove their technical performance.  

Other sustainability points are that clay brick is self-finishing and only requires mortar repointing very occasionally, making it a long-lasting and almost maintenance-free material choice. Bricks require minimal packaging and many brick manufacturers are ISO 14001 certified. 

Movement joints need to be built into brickwork

The anatomy of a brick

Figure 1: Anatomy of a brick 

The long face of a brick is known as the stretcher and the short face is the header. They are often referred to as the finished or fair faces of a brick. It is worth noting that many brick manufacturers only guarantee one good stretcher face and one good header face on their bricks.

The top and bottom faces of the brick, which are usually bedded with mortar, are known as bed faces, while any edge of the brick is referred to as an arris or angle. 

In the larger brick illustrated here, there is a depression in the upper bed face, known as a frog. The smaller brick illustrated shows perforations (holes) in the brick. The purpose of a frog in a moulded brick, and of the perforations in an extruded wire-cut brick, is to make the brick more efficient when firing in the kiln. Frogs and perforations also assist in achieving a strong bond between the brick and mortar.

Understanding movement 

All buildings move, and different building materials move in different ways. While movement cannot be prevented, we can design to accommodate movement. 

Clay brickwork as a material generally expands, while concrete and concrete based products tend to shrink. 

Vertical and horizontal movement joints are required in clay brickwork. If movement joints are not included, internal stresses may result in cracking of brickwork. 

There are many possible causes of movement. Thermal expansion and contraction due to temperature changes and moisture content variation are the two main causes of movement associated with clay brickwork.  

Causes of movement:   

  • Thermal expansion and contraction due to temperature changes 
  • Moisture content variation 
  • Chemical changes such as sulphate attack on the mortar joints 
  • Deflection under loads 
  • Ground movement and settlement.  

Deflection under loads and ground movement and settlement can occur in buildings constructed of any materials. 

Types of movement in brick 

There are two types of movement, reversible and irreversible.  

Irreversible movement: When a brick is fired in a kiln at high temperatures, it becomes extremely dry. When removed from the kiln, the bricks absorb moisture from the air until a normal moisture level is reached. The increase in moisture content causes expansion that is irreversible. Irreversible long-term expansion may take many years. 

Reversible movement: Reversible movement occurs when brick is in use and expands and contracts in response to moisture movement (wetting and drying) and temperature changes (thermal movement).  

The spacing, location and width of movement joints needs to be sufficient to accommodate both irreversible and reversible movement.   

When brickwork moves, in unrestrained or lightly restrained brickwork walls, it expands by approximately 1mm/m during the life of a building, as a result of thermal and moisture movement changes. Not all clay types expand at the same rate.  

Accommodating movement 

Vertical and horizontal movement joints need to be built into brickwork as work proceeds, to allow for movement and prevent cracking.  

In designing to accommodate movement and in locating movement joints, the geometry of the building and its orientation need to be considered. Due to heating from the path of the sun, greater thermal expansion is likely on fully or partially south-facing elevations, particularly where darker bricks are used.  

Brick outer leaf of a cavity wall: If we consider the external wall of a building, with a brick outer leaf to the cavity wall (with the brickwork exposed on one side), movement joints should be no more than 12m apart. The distance from a corner return should be no more than half that dimension in either direction. 

Movement joints are also required within concrete blockwork (at a maximum spacing of 6m apart). Movement joints should ideally be staggered rather than lining up through the outer leaf to the inner leaf. 

Figure 2: For an external wall that has a brick outer leaf to the cavity wall, movement joins should be no more than 12m apart and no more than half that distance from a corner return

Freestanding wall: In a freestanding wall, where there is brickwork to both sides of the wall, movement joints should be included in the wall no more than 6m apart, due to the greater exposure. The distance from a corner return should be no more than half that dimension in either direction, a maximum of 3m. 

Parapet wall: On a wall that has a parapet, for the main part of a wall – where the brickwork is exposed on one side – movement joints should be no more than 12m apart. Where the wall becomes a parapet wall and the brickwork is exposed on both sides, it is more vulnerable to movement and the frequency of joint spacing needs to be increased. In the parapet, movement joints should be spaced no more than 6m apart. 

Movement joint widths: As stated above, the maximum centres between movement joints in the outer leaf of a cavity wall should be 12m apart, as stated in BS EN 1996-2: 2006 Eurocode 6 Design of masonry structures. However, if the 12m maximum spacing is used, each movement joint will be in excess of 16mm wide.  

PD 6697: 2019 – recommendations for the design of masonry structures, clause states that the width of a joint in millimetres should be about 30% more than the distance between joints in metres. To have movement joints 10mm wide (to equal the mortar joint width), movement joints will be required at 7m-8m centres. 

Vertical movement joint: When there is a change in height, change in material or change in wall thickness, a vertical movement joint should be provided. 

There are often points of weakness around openings where forces of tension and compression operate. Where there are large openings in relatively low walls, a vertical movement joint should be located near the point of weakness to accommodate movement or bed joint reinforcement included. 

Movement is likely to occur where there are short returns in clay brickwork of less than 675mm with longer lengths of brickwork to either side of the short return. There is a tendency for the longer lengths of brickwork to expand, resulting in possible cracking. To accommodate this movement, including a vertical movement joint at the short return is recommended.  

Alternatively, the short return can be isolated by including vertical movement joints 1m-2m distance from the return. If the short return is 1m or longer, there may be some distortion of the wall but it is unlikely to cause cracking. 

Figure 3: Movement risk with short returns in clay brickwork 

Different materials: Clay brickwork as a material generally expands, while concrete and concrete-based products tend to shrink. Where brickwork is combined with cement-based products or natural stone, movement joints need to be spaced at a maximum of 6m apart with no more than a 3m distance from corners and changes in direction. 

Where there are different materials used in the external leaf of a building, there should be a movement joint between the different materials. Brickwork should not be set tight within a frame of another material.  

Figure 4: Timer frame shrinkage

Where brick is used to clad a timber-frame building, allowance should be made for the likely shrinkage of the timber. A gap should be left at the top of the brick outer leaf: generally, 12mm for two-storey buildings and 18mm for three-storey buildings. Always consult the timber frame manufacturer. 

Horizontal movement joints: Vertical and horizontal movement in brickwork is considered about the same. In brick buildings that are several storeys high, horizontal joints to accommodate vertical movement should be provided at no more than every third storey or 9m, whichever is less. For buildings not exceeding four storeys or 12m in height, whichever is less, the brick outer leaf will not require a horizontal movement joint. 

In buildings with concrete or steel frames which are several storeys high, it is common to include a shelf angle support at every other storey, combined with a movement joint of reduced thickness. 

Figure 5: Accommodating movement – horizontal movement joints

Brick walls to a radius: Curved brick walls require movement joints at the same maximum spacing as it is for straight brick walls, measured along the curve rather than measured as a chord between two points. Reducing the spacing of vertical movement joints to 7m-8m apart is often considered beneficial and will allow the movement joint width to be 10mm wide. 

Figure 6: Accommodating movement – brick walls to a radius

Movement joint materials 

Filler materials: Filler materials should be built into brickwork as work proceeds and compressible to approximately 50% of their original thickness, suitable materials are: 

  • Flexible cellular polyurethane 
  • Cellular polyethylene 
  • Foam rubbers. 

Note that cork, fibreboard and hemp are not suitable as filler materials because they do not compress easily and do not always recover to their original thickness following compression. 

Sealant materials: As a general rule, the sealant should be applied to a depth at least as wide as the movement joint. Before the sealant is applied, the joint faces must be cleaned of loose particles and primed. Always consult the manufacturer. 

It is strongly recommended that the colour of the sealant to the face of movement joints is specified to blend in well with the brickwork. Movement joints are often noticed when they are finished with a white or black sealant.  

Suitable sealant materials are: 

  • Polysulphide 
  • Low modulus silicon.  

Movement joint locations 

Movement joint locations should be considered as early as possible in brickwork design. One option is to conceal movement joints behind rainwater pipes, but it is essential that the fixings allow for movement of the brickwork. Fixing to one side of the movement joint only is recommended. 

Bed joint reinforcement 

Bed joint reinforcement consisting of parallel bars (also known as ladder or railway track type BJR) may be used to extend the distances between vertical movement joints beyond the 12m maximum recommended spacing.  

Bed joint reinforcement consisting of parallel bars (also known as ladder or railway track type BJR) may be used to extend the distances between vertical movement joints beyond the 12m maximum recommended spacing. 

Figure 7: Dissimilar materials

 Lighter-weight mesh-type bed joint reinforcement will help prevent cracking where there are concentrations of stresses around openings in windows and doors. The project’s structural engineer should always be consulted on this.

Where different materials are used together with brickwork in details such as the stone quoins, lightweight bed joint reinforcement should be included between the two materials, because they have different movement characteristics (see figure 7).

Technical considerations 

 Cavity wall construction: The section on structure in the Building Regulations, Approved Document A, regards the overall weight of a brick wall as forming part of a building’s structural framework. 

Approved Document L (conservation of fuel and power) addresses the thermal insulation of the external fabric of a building and provides calculation methods to determine the thermal performance of a building’s design.

In a cavity wall with a brick outer leaf, the cavity may be either partly or fully filled with insulation. Where the cavity is partly filled, the insulation should be against the inner leaf with a clear air space at a minimum of 50mm behind the brick outer leaf.

Full-fill cavity insulation may require a small residual cavity of 10mm, but it is always best to check the insulation manufacturer’s recommendations and the opinion of the building inspector.

In Approved Document B, volumes 1 and 2 on fire safety, consider where cavity barriers are required.

Stability of brickwork: In cavity wall construction, wall ties are required to tie the outer leaf of brickwork to the structural inner leaf of the cavity wall. 

In Approved Document A, table 5 provides advice on the length of tie related to cavity width, while section 2C8 refers to the spacing of wall ties, which is generally 900mm horizontally and 450mm vertically. 

Where there is a vertical movement joint (unbonded jamb), wall ties are required at a maximum of 300mm apart vertically and within 225mm distance of the joint horizontally. 

To avoid possible mortar displacement, bricklaying should be limited to 1,200mm in height per day, which needs to be recognised by designers and contractors in programming work on site. 

Figure 8: Typical movement joint

 Cavity wall ties: If a shear connection is required between the brick leaves to either side of the movement joint, a flat bar tie with a debonding sleeve may be used. The ties should be prepared for installation by pulling them apart by the same amount as the mortar joint width, to allow the tie to slide as the brickwork expands or contacts to either side of the joint.

 Compliance with UK industry standards 

Certification standards for clay bricks are:

  • BS EN 771-1:2011+A1:2015 – specification for clay masonry units
  • ECO standards ISO 14001:2015.

Other recognised standards that must also be followed are: 

  • BS 8000-3:2020, on workmanship on building sites 
  • Approved Document 7, on materials and workmanship
  • PD 6697:2019, which provides recommendations for the design of masonry structures
  • PAS 70:2003, a guide to appearance and site measured dimensions and tolerance. 

Compliance and adherence to industry standards is essential when selecting bricks and any coatings being applied. All products must comply with the current standards as defined by the British Standards Institution (BSI).

Health and safety and wellbeing 

Bricks are dense, heavy and potentially dangerous if not managed correctly on site, so it is essential that health and safety best-practice standards are followed.

The CDM Regulations 2015 state that designers have the responsibility when preparing or modifying designs to eliminate, reduce or control foreseeable risks that may arise during construction and during maintenance and use of a building once it is built. 

In addition to the CDM Regulations, on site the following should be taken into account:

  • Health and Safety at Work Act 1974
  • Management of Health and Safety at Work Regulations 1999, requiring employers to carry out risk assessments, make arrangements to implement necessary measures, appoint competent people and arrange for appropriate information and training 
  • Control of Substances Hazardous to Health Regulations 2002 (COSHH), requiring employers to assess the risks from hazardous substances and take appropriate precautions.

Dry cutting of bricks should be avoided, to reduce the production of dust which may contain silica or quartz particulate, as this causes silicosis. A suitable respirator or FFP3 standard mask should be worn. Ear defenders to protect from noise and safety goggles to protect from splinters or chips should also be worn by those cutting bricks and those working in the vicinity. 

British Standard BS 8000-3:2020, on masonry workmanship on building sites, offers best-practice guidance for dealing with bricks, and most reputable manufacturers will also have appropriate documentation and guidelines available. 

Post-construction maintenance of brickwork

Clay brickwork is extremely durable and requires minimal maintenance. Periodic inspection as part of facilities management procedures is recommended to check whether repairs and maintenance are required, such as mortar joint repointing, unclogging of weep holes and removal of crawling vegetation.

There may be a need to clean brickwork due to the effects of pollution in densely populated urban areas, accidents, poor maintenance and vandalism. Before carrying out any cleaning of brickwork, the manufacturer’s recommendations should be referred to and the health, safety and environmental requirements must be considered. Specialist cleaning contractors may be required.

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