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
- Bricks in the 21st Century
- Brick production methods
- Types of brick
- Sustainability

            
                    
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.                     
                                     
            
    

Learning Aims

TechConsideration26

This seminar looks at the most important technical issues that need to be taken into consideration when designing with clay brick.

Product selection, brick properties, expansion joints and mortar are all discussed with a focus on how this can affect design and detailing. The presentation also looks at standards, sustainability and construction methods.

  • To provide an overview of modern brick manufacturing processes, terminology and the characteristics of different products.
  • Knowledge of technical properties in accordance with the product standard BS EN 771-1.
  • Explanation of size tolerances.
  • Understanding the influence of design and detailing on brickwork performance.
  • Insight into the principles of brickwork expansion joints and mortar specification.
  • To discover why brick is sustainable.

Why Brick?

TechConsideration36
  • Wide product range allows unlimited design possibilities.
  • Natural and sustainable building material.
  • Highly economical.
  • No expenses for maintenance and repairs.
  • Durable and stable in value over many generations.
  • Maximum energy efficiency of the building envelope.
  • Healthy indoor climate conducive to well-being.

Brick in the 21st Century

TechConsideration32
Carmelite Monastery, Liverpool
Austin-Smith:Lord

Almost everyone knows that brick is one of mankind’s oldest and most durable building materials. It is increasingly being used in new, fresh and innovative ways.

By specifying brick, your designs will ‘stand the test of time’. Brick leaves a long lasting legacy that will be a testament to your vision for many hundreds of years.

But what are the technical considerations to ensure that brickwork will remain beautiful…

Architects are re-engaging with brick in new and innovative ways

When we talk about bricks, people think that we talk about tradition. But you can find many brick buildings with a new, modern approach, and they give brick a new meaning and a new appearance. It all depends on how innovatively you use brick.” – Wang Shu, Architect and Pritzker Prize Winner, Jury member of the 2014 Wienerberger Brick Award

Production Methods

There are several types of clay bricks made in different ways, each with differing characteristics.

Modern clay bricks are formed in one of these four processes…

  • Soft Mud Moulded Stock
  • Waterstruck
  • Extruded / Wirecut
  • Semi-Dry Pressed

With information from the BDA we see how the divisions for different brick types are in the UK.

Brick_TechCons_PieChart
TechConsideration61
Handmaking

Handmaking

Hand making involves the forming of the clay by hand, coating in sand and throwing into a mould.

The moulding process has been used for centuries, using a ‘stock’. The bottom section illustrated would be fixed to a bench – the raised profile in the middle helping to spread the clay to the four corners to achieve a reasonable brick shape.

When the brick is inverted, the resultant cavity (commonly called a ‘frog’) can be seen.

Handmaking

  • The moulding process has been used for centuries using a ‘stock’.
  • Handmaker forms roughly shaped clot of soft clay
  • Clot is coated with sand and thrown into pre-sanded mould box
  • Kicker placed on mould bottom to form frog – Frogs help spread clay to corners of mould
  • Typical handmaker produces around 100 bricks per hour
  • Now a niche method of traditional production – Lower volume, prestigious market
TechConsideration62
Modern Machine Manufacturing

Modern Machine Manufacturing

Machine manufacturing of soft mud bricks follows the processes of hand making, just automated and it varies in that stocks have the clay pressed into the mould rather than being thrown or dropped into the mould.

‘Handformatic’ brick ranges recreate the hand thrown technique by throwing the clay into sanded moulds using belts, creating the signature smile.

Modern Machine Manufacturing

  • Soft mud clay is pressed into the sand lined moulds and as they rotate bricks are turned out onto drying trays
  • The close simulation of hand throwing creates crease patterns on brick faces
  • Outputs can be as high as 22,000 bricks per hour
TechConsideration63
Waterstruck/Slop Moulded

Waterstruck/Slop Moulded

Soft Mud Moulding actually covers a number of manufacturing processes where bricks are formed using mould boxes. One of these is the Waterstruck process.

Clay preparation is critical in order to get the correct consistency/plasticity. In this instance water is used as a releasing agent to prevent the clay sticking to the box (instead of sand). The excess clay is struck off from the top of the mould as the bricks are turned out – This is where the term Waterstruck originates.

Waterstruck / Slop Moulded

  • Niche method of traditional production
  • Soft mud clay forced through dies into moulds
  • Release from moulds facilitated by water instead of sand
  • Use of water creates distinctive texture – brick looks old and handmade even when new
  • Bricks generally manufactured as solid
TechConsideration2
Extruded/Wirecut

Extruded / Wirecut

For Extruded bricks clay is forced through a die to create a long column of material of the desired width and depth.

The column is then cut into smaller, more manageable pieces approx 1.5m in length known as ‘slugs’. This is then cut into bricks of the desired length by row wires.

The introduction of perforations reduces the volume of clay needed, and hence the cost. Perforated bricks require less energy for drying and firing and are also lighter and easier to handle.

Extruded / Wirecut

  • Most popular method of production
  • High volumes – Circa 20,000 bricks per hour
  • Plastic clay mix driven through extrusion head to form continuous column
  • Column cut into slugs and subsequently bricks (nominally 215 x 102.5 x 65mm)
  • Perforations formed by extrusion core bars,generally ≤30% volume
  • Perforations save clay, reduce drying and firing cycles and save weight = more efficient transport

Brick Types

TechConsideration3
Firing

Firing

With all manufacturing processes the wet bricks are then dried and fired. The firing process provides the inherent durability, strength and fire-resistance associated with clay construction products.

Clay bricks are a natural product therefore colours may differ slightly from one production run to another.

The mixing of bricks from packs will provide a good balance of colour, particularly with ‘multi’ coloured products, and help to prevent ‘colour banding’ within elevations of finished brickwork.

Unless advised otherwise, we would suggest mixing from a minimum of 3 packs.

Firing

  • After drying, the products are transferred to a tunnel kiln where they fired.
  • Typical peak firing temps range from 1020°C to 1100+°C.
  • This high temperature is necessary to establish the inherent durability, strength and fire-resistance associated with clay construction products.
  • Bricks are normally in the kiln for 2-3 days (cold to cold).

Common Brick Terminology

  • Stretcher – The longer face of brick showing in the surface of a wall
  • Header – The end face of a standard brick
  • Bed Face – The face of a brick usually laid in contact with the mortar
  • Arris – Any straight edge of a brick formed by the junction of its faces
  • Frog – An indentation in one or both bed faces of moulded or pressed bricks
  • Perforation – Holes through extruded bricks from bed face to bed face
TechConsideration5
Soft Mud Moulded Stock

Soft Mud Moulded Stock

When laying frogged bricks the frogs should be fully filled with mortar which is why we recommend that bricks are laid with the frog up.

This ensures that a full bed of mortar can be applied and will maximise the brickworks structural performance providing a more stable wall with better sound insulation.

The laying of bricks frog down will not in itself disadvantage the durability of the individual brick units as the product would be expected to perform regardless of its orientation.

Soft Mud Moulded Stock characteristics

  • Lower compressive strength
  • Higher water absorption
  • Traditional appearance
  • Sanded face
  • Frogged
  • Multi-effect colourings
  • Softer and warmer brick aesthetic
TechConsideration6
Waterstruck/Slop Moulded

Waterstruck / Slop Moulded

This process forms a relatively smooth, sand free texture. Use of water creates distinctive texture – brick looks old and handmade even when new.

Waterstruck / Slop Moulded characteristics

  • Relatively smooth
  • Unsanded face
  • Irregular texture
  • Multi-effect colourings
  • Reclaimed appearance
TechConsideration7
Extruded/Wirecut

Extruded / Wirecut

This process produces hard, dense bricks with a more regular size and shape, sharper arises and a more contemporary appearance.

 

Extruded / Wirecut characteristics

  • High compressive strength
  • low water absorption
  • Very consistent size/shape
  • Sharp arrises
  • Contemporary appearance
  • Vertically perforated
  • Grooved rear face
TechConsideration8
Engineering Bricks

Engineering Bricks

Engineering bricks are only required to meet specific compressive strength and water absorption performance criteria. They fall in to two classes and are commonly used at DPC level, although most bricks can be used below DPC.

 

Class A Engineering Bricks
Compressive strength ≥125N/mm²
Water absorption ≤4.5%
Blue coloured
Solid only

Class B Engineering Bricks
Compressive strength ≥75N/mm²
Water absorption ≤7%
Red or blue coloured
Solid and perforated

Engineering Bricks

  • The term ‘engineering bricks’ is used in the UK to define a specific group of bricks with specific properties.
  • Sold on their technical performance and used in applications where appearance is not a major consideration e.g. below DPC.
  • Variation in colour and any other surface irregularities which do not detract from the technical performance are not considered to be unsatisfactory.
TechConsideration9
Brick Slips

Brick Slips

Brick slips provide the desirable finish of real brickwork in situations where using full bricks may not be possible.

  • Maintain the look of real brickwork
  • Suitable for soffits, arch sets, prefabricated elements, internal use
  • Slip returns also available for corners and reveals
  • Can be cut to required thickness. Recommended minimum 20mm for traditional stock brick types. 15mm for extruded brick types
  • Adhesive bonded to backing material

Sustainability

TechConsideration10
Sustainability

Why is Brick Sustainable?

Bricks are a versatile and durable building material with excellent life cycle performance, energy efficiency, high thermal mass and responsible manufacturing.

The BRE’s Green Guide to Specification assigned the highest possible accreditation (A+) to every external wall it rated that contained brick.

Management systems help manufacturers to continually improve upon their performance.

  • Bricks are a versatile and durable building material with excellent life cycle performance, energy efficiency, high thermal mass and responsible manufacturing.
  • Clay bricks have received an A+ rating in BRE’s Green Guide
  • ISO 14001 – Environmental Management System
    Enables organisations to identify, evaluate and minimise environmental impacts associated with the provision of products or services.
  • BES 6001 – Responsible Sourcing of Construction Products
    Provides assurance to customers of responsible sourcing and supply chain management.

Although bricks are considered to have high embodied energy due to the manufacturing process, it is important to take the materials whole lifecycle into account when measuring sustainability, not just the amount of energy consumed in the making of that material.

With a lifespan of 500 years plus, any embodied energy within the brick from the manufacturing process is written off over a very long period, enabling brick to be a very sustainable product.

 

Brick and brick buildings are sustainable because they:

  • Are highly durable.
  • Offer long term life performance.
  • Are low maintenance.
  • Are energy efficient.
  • Provide healthy and comfortable environments.
  • Are recyclable.

Brick Properties

TechConsideration12

Like colour and appearance brick properties are a result of a number of factors: Raw material, Manufacturing process, Firing temperature.

Factors influencing the choice of brick for a project include geographical location, position and orientation of the building and potential exposure to wind driven rain.

Technical Properties

These terms are common with all brick types.

The Declaration of Performance declares the technical performance of a construction product against the relevant harmonised European standard.

The values for each brick are on our DoP’s and also downloadable in our COBie files within our BIM objects.

Technical Properties

  • All clay bricks are manufactured to the European Standard 

BS EN 771-1

 

Manufacturers are required to declare technical properties including:

  • Durability
  • Compressive Strength
  • Water Absorption
  • Active soluble salt content
  • Size tolerance and range

The values for each brick are available on the unique product Declaration of Performance.

Durability

Bricks last. You only need to look around at our many historical buildings to see how brick stands the test of time.

Brick is a solid, permanent and low maintenance material that provides lasting beauty and appreciating value – brick offers true longevity.

Durability

  • Clay masonry has a service life of +150 years, easily outperforming most other materials.
  • Clay bricks retain their shape and colour, even after long exposure
    to the elements.
  • Bricks are completely incombustible and are able to retain their mechanical strength during fires.
  • The high stability and density of clay masonry enables it to withstand water pressure very well making it very flood resistant.
TechConsideration13
Durability Classifications

Durability Classifications

These terms are common with all brick types.

An F2 durability rating means that the product is suitable for more exposed building details where units may be saturated and subjected to repeated freezing and thawing, this includes use below DPC level.

 

F1 bricks are only moderately frost resistant. They should not be used in saturated conditions or where they may be subjected to repeated freezing and thawing. They cannot be used below DPC or for garden and retaining walls, chimneys, parapets etc.

F0 bricks are liable to be damaged by freezing and thawing and are only suitable for use internally or behind impervious cladding.

Durability Classifications

For clay bricks there are 3 categories of frost resistance:

  • F2 – Frost resistant
  • F1 – Moderately frost resistant
  • F0 – Not frost resistant

To ensure satisfactory performance the choice of brick also needs to be complemented by appropriate design and detailing.

TechConsideration14
Frost Failure

Frost Failure

Frost attack occurs through a combination of excessively wet brickwork and repeated freeze/thaw cycles.

When water turns to ice, there is a 9% increase in its volume. This expansion can produce stresses within the brick eventually leading to spalling, with the brick face flaking off and/or crumbling.

 

Failure through frost attack is usually confined to areas of severe exposure, or where the frost resistance of the brick was incorrectly specified.

Particular features which are vulnerable include chimney stacks, parapets, aprons under windows, garden walls, retaining walls and bricks below DPC level. Plain vertical walls are not a high risk if they are adequately protected by roof overhangs, projecting cill details etc.

Frost Failure

  • Frost attack occurs through a combination of excessively wet brickwork and repeated freeze/thaw cycles.
  • Failure through frost attack is usually confined to areas of severe exposure, or where the frost resistance of the brick was incorrectly specified.
Bricks Below DPC Level.
Bricks Below DPC Level. In this case the brickwork is naturally going to get wet at the base from rain water and splashing from the surface of the paving. Adjacent paving should be laid to falls, sloping away from the wall, to reduce the saturation risk.  Drainage channels or drained gravel filled margins will further reduce saturation at the base of the wall.

Bricks Below DPC Level

F2/S2 rated bricks are suitable for use below DPC level. A brick in wet conditions can appear darker in colour and this may be apparent below DPC level from time to time. There may also be an enhanced risk of staining due to the wetter conditions.

Bricks Below DPC Level

  • F2/S2 rated bricks are suitable for use below DPC level.
  • A brick in wet conditions can appear darker in colour and this may be apparent below DPC level from time to time. There may also be an enhanced risk of staining due to the wetter conditions.
  • Adjacent paving should be laid to falls, sloping away from the wall, to reduce the saturation risk.
  • Drainage channels or drained gravel filled margins will further reduce saturation at the base of the wall.

Compressive Strength

The inherent strength of clay bricks has always been well known.

The tallest iron frame commercial building with a load bearing masonry external wall ever constructed. 16 storeys high with walls 1.8m thick at the bottom and 46cm thick at the top.

Compressive Strength

  • The inherent strength of clay bricks has always been well known.
  • Compressive strength is expressed in N/mm²
  • Extruded facing bricks tend to have a higher compressive strength compared to soft mud, moulded bricks due to their higher density.
  • Compressive strength is NOT an indication of quality or durability.
TechConsideration17
Water Absorption

Water Absorption

Water absorption is common amongst all clay bricks, manufacturers will publish the individual rates for their ranges.

BS EN 772-21 test is carried out – 24 hour cold soak. Bricks are weighed before and after to determine change in mass.

Some intermittent darkening due to moisture should be regarded as a normal characteristic of brickwork. This can be more obvious with moulded, soft mud bricks with a higher water absorption.

Water Absorption

  • All clay bricks can absorb some water.
  • Water absorption figures range from ≤4.5% for Class A Engineering Bricks to ≤24% for some moulded, soft mud bricks.
  • Water absorption is NOT directly related to durability.

Water Absorption

Bricks and brickwork, i.e. the bricks plus the mortar joints, are not waterproof, hence why modern buildings are built using some form of cavity wall construction.

Cavity wall construction and correct detailing will cope with any water penetration through the outer leaf.

Water tends to penetrate brickwork through the mortar joints or via the brick/mortar interface, rather than through the bricks themselves.

Water Absorption

  • The water absorption of bricks is something that needs to be taken into consideration as part of design and detailing.
  • In cavity wall construction it is expected that some water will penetrate the outer leaf.
  • Correct design and detailing (DPC‘s, cavity trays etc.) should prevent water entering the building.
  • Water repellent surface treatements or sealants are not recommended for clay brickwork.
TechConsideration18
Parapets, Cappings and Cills

Parapets, Cappings and Cills

Some of the areas where the water absorption of bricks can become more apparent is with brick parapets, cills and cappings.

The use of a metal or concrete coping or cill is recommended to help shed water and offer greater protection from the elements.

Parapets, Cappings and Cills

  • Brick parapets are generally more exposed to the elements.
  • Brick on edge cappings are at risk of heavy saturation and water will run off be able to track down through the brickwork, as appears to have occurred here (a detailing issue may have exacerbated the situation in this case).
  • The use of a metal or concrete coping or cill is recommended to help shed water and offer greater protection from the elements.
TechConsideration19
Active Soluble Salt Solution

Active Soluble Salt Content

Water soluble salts occur naturally in the raw materials used to make bricks and mortar.

  • Water soluble salts occur naturally in the raw materials used to make bricks.
  • There are prescribed limits for water soluble compounds of Sodium [Na] Potassium [K] and Magnesium [Mg].
  • The European Standard classifies the lower limit of the above salts as S2 and a higher limit as S1.

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

Which of this is not a modern production method for 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

Which of these is an incorrect brick type and attribute combination?

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

BS EN 771-1 does not requires manufacturers to declare which of these technical properties?

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