Products > Brick

RIBA Core Curriculum
- Design, construction and technology

Knowledge level
- General Awareness

This course provides an overview of the modern brick manufacturing processes, the common terminology and the characteristics of different products. It covers topics such as brick technical properties, British Standards including BS EN 771-1, the influence of design and detailing on brickwork performance and the principles of brickwork movement, expansion joints and mortar specification.

In this section
- Mortar specification and why it should be an important consideration
- An introductory look at movement in brickwork
- Thermal and moisture movements and calculations
- UK and European Standards

            
                    
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.                     
                                     
            
    

Mortar

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It is important that the appropriate mortar specification for different applications is considered.

The mortar specification will depend on a number of factors such as the application, location, level of exposure, other site specific conditions.

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Effect of mortar colour on brickwork appearance

Mortar accounts for 17% of the visible brickwork (dependant on bond pattern) and the colour chosen can change the look of a wall considerably.

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Mortar Specification

Mortar Specification

Mortar strength is an important consideration, the choice of which will be affected by such factors as weather, degrees of exposure, location and loadbearing requirements.

A suitable reference panel should be constructed prior to commencement of brickwork in order to provide an indication of the finished wall appearance.

 

The reference panel should set the standard for appearance and workmanship for all of the brickwork to be completed and should be built with the correct bond pattern, mortar colour and joint profile.

The initial rate of water absorption, also known as the suction rate, is of importance in the laying of bricks.

The figures included on the brick Declaration of Performance should allow the contractor/mortar supplier to tailor the mortar to suit the bricks.

Brick with a high suction rate may need to be wetted prior to laying, particularly in hot, dry weather. Bricks with a very low suction rate (e.g. blues) can float on the mortar if they become saturated or if the mortar is too wet.

Mortar Specification

  • There are a number of factors that will influence mortar specification such as location, brick type, level of exposure, site specific conditions etc.
  • The primary method of designation for mortar is the strength grade.
  • Although stronger mixes are more durable, the mortar strength should also relate to that of the brick.
  • Lime mortars are becoming popular again and should be specified with the assistance of a specialist supplier.

Typically we would suggest a Designation (iii) / Class M4 mortar for general brickwork areas in the walls of buildings.

For more exposed details, for example below DPC level, parapets, chimneys, garden/retaining walls etc. a Designation (ii) / Class M6 mortar would be more appropriate.

Designation (i) / Class M12 mortar is the most durable but is more suited to engineering type bricks.

 

It is preferable to use pre-mixed mortars which have the advantage of accurate blending and minimal variation in colour.

We would recommend speaking to a mortar supplier for more specialist advice, taking into account the brick properties and the target strength required.

The mortar joint profile has a significant impact on the aesthetics of a wall. It also plays an important part in the overall weather resistance of brickwork so the choice of joint profile used should be based on technical performance requirements as well as appearance.

Correct proportioning of mortar constituents is required to achieve adequate strength, a good bond and to avoid colour variation.

Gauging by mass using batching boxes is the most accurate method and water content should be accurately controlled.

Proportioning by volume using shovels should be discouraged.

Cross and bed joints should be fully filled and joints should be well tooled.

A bucket handle joint is usually favoured as it provides an attractive appearance combined with good weather resistance.

Recessed joints are not recommended in locations liable to severe exposure to wind-driven rain or in external works e.g. boundary walls because they impede water run-off and the overall weather resistance of the brickwork is reduced.

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Creative Use of Mortar

This small, brick built hunting lodge was designed by Nikolaus Bienefeld of Buro Bienefeld.

Wide joints and flush pointing create an archaic simplicity.

Demonstrates how well brick architecture can fit into rural areas.

Movement in Brickwork

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Now let’s take a look at movement in brickwork. This is a complex subject that cannot be completely covered here but we have a separate CPD seminar devoted to just this topic if further information is required.

We are not concerned in this presentation with structural, 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.

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.

Movement of brickwork should be considered at the design stage. The main sources of movement relate to moisture and temperature.

 

In general, reversible movements are caused by temperature changes. Irreversible expansion (caused by adsorption of water molecules by the fired clay brick) can be larger and continues, albeit at a reducing rate, for a period of years.

  • All building materials are subject to movement.
  • This movement is due to a number of reasons including:
  • Thermal expansion and contraction due to temperature changes
  • Moisture movement
  • Creep and structural loading
  • It is the first two of these which are particularly influential on masonry movement.
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Why don't we see movement joints in historic buildings?

Why don’t we 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 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.

Thermal Movement

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Thermal Movement

Every material has a co-efficient of expansion – this varies with different clay types although the difference 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.

Thermal Movement

Thermal expansion of the brick will occur due to the range of temperatures experienced, the orientation of walls and the colour of the brick

Reversible (+/-)

  • Co-efficient of Expansion
  • 4 – 8 x 10-6 / K

Moisture Movement

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Moisture Movement

The wetting and drying process will have an effect on the overall movement, although this is negligible.

Irreversible expansion occurs following a reaction at a molecular level as the bricks are exposed to the ambient atmosphere.

Moisture Movement

A greater influence on the overall movement of clay bricks is the long term effect of moisture

Reversible (+/-)

  • + 0.02%
  • Negligible (0.2mm/m)

Irreversible (+)

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

Overall Movement Calculation

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%.

The reversible (wetting and drying) effect is in the order of 0.02%, and taking the worst case irreversible moisture expansion (0.07%), we arrive at a total theoretical movement of just over a millimetre per metre run of brickwork.

 

It is highly unlikely that all three elements will be acting together but nevertheless it is useful to offer a guideline of 1mm/ metre for the provision of movement joints.

Different technical characteristics, e.g. strength, water absorption etc. 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, sensible provision of movement joints will avoid any issues.

Overall Movement Calculation

  • Thermal – 1000mm x (6 x 10-6) x 45oC = 0.27 (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
  • Different manufacturing methods and technical characteristics of bricks do not affect the principles of movement joint provision.

Guidance

Movement of brickwork should be considered at the design stage.

As a general rule in buildings, brickwork expansion joints should be provided every 10-12m maximum.

This dimension reduces to 6m in boundary walls or brick faced parapets.

  • As a general rule in buildings vertical movement joints should be provided every 10-12m maximum.
  • This dimension reduces to 6m in freestanding walls, retaining walls or brick faced parapets.

Movement in Brickwork

There are a number of building features which need to be considered carefully when determining joint positions.

This is a typical detail where a rebated (or pistol) brick is able to accommodate the shelf angle support, avoiding an excessive horizontal joint; brickwork below the angle can expand vertically compressing the filler material.

Movement in Brickwork

  • Features of the building which need to be considered when determining joint positions are:
  • Short returns and changes in direction on plan.
  • Changes in height.
  • Different materials within the external leaf.
  • Window and door openings.
  • Southerly elevations which are more susceptible to temperature changes.

Movement Joint Materials

An indication for normal storey height walls is that the joint width (in mm) should be at least equal to the joint spacing (in m) plus an allowance of typically 30% to allow for the compressibility of the filler and the performance of appropriate sealants – Thus movement joints at 10m centres will need to be approximately 13mm wide.

Movement Joint Materials

  • The material for filling movement joints should be easily compressible to approximately 50% of its original thickness. Flexible cellular polyurethane, cellular polyethylene or foam rubbers are satisfactory materials.
  • Movement joints should be sealed with a polysulfide or low modulus silicon which has sufficient flexibility to accommodate movement and be resistant to water penetration.
  • To allow for the compressibility of the movement joint filler, the width of the joint in millimetres should be about 30% more than the distance between joints in metres. For example, movement joints at 12m centres should be 16mm wide.

Bed Joint Reinforcement

Masonry Reinforcement is a fabricated steel reinforcement system that is located in the bed joint to strengthen masonry panels without thickening the wall.

Bed joint reinforcement may be used for a variety of purposes and locations, including:

  • Increased brickwork panel sizes
  • Increased movement joint spacing
  • Stack-bonded panels
  • Differential movement control
  • Above and below openings to prevent cracking

A structural engineer should be consulted to assess the spacing of control joints and bed joint reinforcement.

Bed Joint Reinforcement

  • The use of bed joint reinforcement can provide some control over cracking.
  • Reduces the risk of cracking at stress concentrations around openings or as a result of movement.
  • Improves the structural performance of masonry walls by providing additional resistance to lateral loads e.g. wind.
  • Used in stack bonded brickwork to compensate for the lack of natural overlap and provide more restraint.

Differential Movement

When brickwork is to be used to clad a reinforced concrete or timber frame, the design should make particular allowance for differential movement.

Vertical movement can be cumulative, and with external brickwork expanding, and the frame potentially contracting, it is often more practicable to deal with movement in smaller sections.

Differential Movement

  • When brickwork is used to clad a reinforced concrete or timber frame, the design should make allowance for differential movement.
  • Clay brickwork will generally be subjected to long term expansion
  • Concrete masonry, aggregate blocks and aircrete blocks will be prone to shrinkage.
  • Brick cladding to timber framed buildings should be designed to prevent cracking as a result of stresses generated by vertical differential movement between the brickwork and the timber frame. Allowance – 6mm per storey height Ref. PD6697 cl. 6.2.6.8.

Standards

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Standards

There are a number of standards that relate to brickwork, these are available from BSI.

Clay bricks are manufactured and tested in accordance with the European Standard BS EN 771-1.

Eurocode 6 comprises the following parts:

Part 1–1, General rules for reinforced and unreinforced masonry structures.

Part 1–2, Structural fire design.

Part 2, Design considerations, selection of materials and execution of masonry.

Part 3, Simplified calculation methods for unreinforced masonry structures.

Each part also has a National Annex (NA) which provides the Nationally Determined Parameters (NDPs) to be used in the application of Eurocode 6 in the UK.

PD 6697 contains useful guidance complementary to Eurocode 6.

Standards

  • BS EN 771-1:2011

Specification for masonry units. Clay masonry units

  • Eurocode 6
  • PD6697:2010

Recommendations for the design of masonry structures to BS EN 1996-1-1 and BS EN 1996-2

  • BS 8000-3:2001

Workmanship on Building Sites – Part 3: Code of Practice for Masonry

  • PAS 70:2003

HD clay bricks. Guide to appearance and site measured dimensions and tolerance

Summary

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Summary

Brick has developed from being a traditional, plain building material into an innovative, modern and adaptable material providing solutions for the entire building envelope.

By understanding the technical considerations and following the guidance on design and detailing you can ensure that clay brick will retain its quality and beauty.

Learning Outcomes

Learning Outcomes

We have looked at the key technical considerations to enable the successful specification and execution of brickwork:

  • Knowledge of modern brick manufacturing processes and the characteristics of different products.
  • How brick properties can affect performance.
  • Material selection based on application and location.
  • Understanding of size tolerances and brickwork setting out.
  • Mortar specification based on strength class.
  • Understand the principles of brickwork movement.
  • Relevant standards/codes of practice for brickwork.

Thank you

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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.

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Depending on bond pattern, mortar tytpically accounts for what percentage of the visible brickwork?

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Which of these is not a typical purpose for bed joint reinforcement?

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