Brick

Fired clay brick is a significant part of Scotland’s built heritage, although it’s not as common a masonry type as stone. Clay is the basic raw material used to make bricks. It is shaped into a brick, allowed to dry and then fired in a kiln.

Bricks vary greatly in type and qualities, just as stone does, making different kinds of brick more suited to particular purposes. Raw clay can be moulded into almost any shape.

Bricks found in common use in Scotland fall into the five main types below.

Common bricks

This is the term for any type of everyday brick with no special properties. Good quality common bricks, when looked after, are a versatile and strong building material. Some can be almost as dense and durable as engineering bricks. Others such as ‘colliery’ bricks, made of clay mixed with shale waste, can be weaker and more porous. Poorer quality bricks were meant to be harled or used internally and will need more care if exposed to the weather.

Facing bricks

These are better quality and more durable than most types of common bricks. They are also likely to be denser and have a smoother surface and uniform colour. Facing bricks were traditionally made for use on principal or exposed elevations.

Glazed bricks

Often mistaken for tiles, glazed bricks were used mainly where hygiene or light were important. Glazed bricks came in many colours and shapes, so were also used for decoration. Machine made and precise in shape, glazed bricks could be set with very fine mortar joints to make striking visual effects.

Special bricks

Non-standard shapes and sizes of bricks were used next to the usual rectangular shape to create standard architectural features or a bespoke function or look. Special bricks were often made from white or yellow clay for use in polychromatic decoration. The most common special brick types include bullnose, coping, arch, circle, splayed and air bricks.

Engineering bricks

These are made from high quality clay and in such a way that they are very dense, impermeable and able to withstand greater compressive pressures. Best quality, Class A (blue) or Class B (red) engineering bricks are available. Highly durable, they were used in the past to build bridges, tunnels, lighthouses and parts of buildings more vulnerable to damage and decay.

Cleaning traditional brickwork should be done very carefully, if at all. Much damage has been caused to brick buildings by incorrect cleaning.

The safest way to avoid the risk of damage to a brick building from any form of cleaning is simply not to clean in the first place.

If you’re thinking about cleaning brickwork, you should:

• seek expert advice
• only clean if strictly necessary
• try cleaning with water first to avoid the unnecessary use of chemicals
• ensure that the cleaning method is first tried out on small test panels
• use an experienced contractor fully trained in the method to be used

Cleaning with water

The most suitable and risk-free way to remove modest soiling is to wash down brickwork using water and a non-ferrous bristle brush (ferrous metals will damage brick).

Take care to avoid:

• exposing the brick to too much water
• lower areas being saturated by the run-off from above
• vigorous scrubbing as this could let water into the brick
• using water at high pressure – a high-pressure hose will force water deep into the structure

Systems that use super-heated water and steam can be very good at removing some forms of biological growth, paint and even bitumen. But care must be taken not to damage nearby woodwork, glass or other materials.

Chemical cleaning

Chemical methods involve applying a substance that reacts with the brick and any discolouration on its surface. The chemical is then removed, along with the soiling.

Such techniques have often changed the affected building permanently. Because brick is porous, no matter how good the attempts to ‘rinse off’ the chemicals, some residue will always be ‘rinsed into’ the brick. Acid cleaning is particularly likely to damage glazed bricks.

Chemical cleaning may lead to:

• irreversible discolouration of the brick
• the breakdown of the brick ‘fire skin’ (outer surface)
• faster decay of mortar
• unsightly white salt deposits left on the surface

Most of these changes can also speed up the decay of brickwork.

Abrasive cleaning

A variety of soft, round abrasives, designed to cause less damage to the brickwork, are available as are various systems of application. These are generally blown onto the surface by pressurised air. In skilled hands, these may be suitable for cleaning traditional brickwork.

Mechanical abrasive cleaning using hand-held devices should be avoided. It can remove the fire skin of bricks, leaving them pitted and more prone to decay.

Sand or grit blasting must never be used. It will quickly remove the surface of bricks and lead to rapid re-soiling, leaving brickwork open to decay and damage.

Brickwork will decay over time if a building isn’t properly maintained. You should inspect a brick building regularly and address the root cause of any small defects before bigger problems emerge. Below are the main warning signs to look out for.

Algae or green staining

This is caused by water running down the surface or getting inside brickwork, leading to saturation. Faulty rainwater goods are often the culprit. Normal exposure to moisture, such as rain alone, will not cause algal growth.

Plant growth

Mosses and lichens can hold moisture against the surface of bricks and mortar, helping more water to get into the brickwork. Ivy and other creepers can grow through and wrap around bricks, causing serious structural instability or failure. The roots of larger plants can dislodge bricks and pointing, leading to cracking and structural damage.

Efflorescence

A white bloom on the surface of brickwork is usually a sign that the wall has become saturated, causing salts from the core to be drawn to the surface. Cement repointing is the most common source of efflorescence in brickwork, though winter salt and other contaminants can also cause serious damage. If salts are formed inside the brick, spalling can occur.

Loose or missing mortar

Crumbling or missing mortar is often simply the result of exposure to many decades of rain and frost. Most lime bonded walls will need repairs to the pointing every 50 years or so. But mortar will decay at a much faster rate in walls subjected to prolonged exposure or excessive moisture. Find out about assessing the need to repoint.

Spalling

Spalling will occur where bricks are constantly saturated by water due to poor maintenance and then exposed to frost. It causes the flaking of the brick surface known as the ‘fire skin’ and, ultimately, the complete deterioration of the brick. Dry masonry isn’t damaged by frost, so it’s vital to keep brickwork free from saturation.

Cracks

These may signal structural problems, particularly if they run through both bricks and mortar and continue to widen over time. Some cracks may have occurred soon after construction and present little or no danger to brickwork. Monitoring cracks for a time can tell you if they’re active or not.

One of the most common and serious problems to affect brickwork is water getting into the brick. Most brick decay is caused by excessive moisture.

Water may come from sources such as:

• blocked or damaged rainwater goods – over time, even small leaks can cause saturation of brickwork
• failed underground drainage – this can cause water to saturate the ground next to the foot of walls so that moisture then enters the brick
• failure of copes – rather than being thrown off the building, water will run down the face of brickwork, causing saturation of upper areas
• roof and other junctions – significant damage can result to brickwork if roofing leadwork fails and lets water into the junctions beneath
• condensation – a build-up on the inside face of a wall, most often in basements, can lead to the ongoing saturation and decay of brick

Cement repointing

Cement repointing is another major cause of decay to brickwork. Cement is hard, brittle and impermeable, and it cracks easily. These cracks draw in water, and the cement then traps the moisture in the wall. The gradual saturation of the wall will give rise to decay, and it can also put pressure on nearby building elements, causing further damage.

Using cement mortar for repairs is also the most common cause of the movement of soluble salts in brickwork.

Salt damage

Salt damage can also occur from a variety of other sources, including sea spray or winter salt used on pavements or roads by buildings.

Salt is soluble and so can be washed into the brick by rain and ground water. As the water evaporates, salt can be left inside the brick. When too much salt builds up in the brick, the salt crystals will exert pressure, causing the brick to break down. The result is a loose powdery surface with a white appearance.

To help prevent this, winter salt should be applied well away from the stone courses near the ground.

Frost damage

Frost damage is another culprit. Bricks vary greatly in their ability to tolerate frost. Water can more easily enter porous bricks and so their frost resistance is much poorer than that of denser bricks. Frost damage results as the water expands within the brick when it freezes. You will probably have to replace the affected bricks if such damage occurs.

Cracking in brickwork is the most common sign of structural movement. This may be caused by:

• unstable ground or foundations
• physical damage
• tree roots
• defects in the original construction

Minor cracking will be superficial and affect only a small area. It may be necessary to carefully cut out cracked mortar and repoint the bricks using lime mortar. In other cases, a few fractured bricks may instead need to be replaced.

Extensive cracking can be a sign of a serious problem. You should seek professional advice on its cause and repair.

Look out for any areas where the wall face projects out from the adjacent build. This is usually a sign that structural movement has displaced bricks. Ledges created in the process may allow water to gather and get into the building fabric.

Saturation of foundations can lead to leeching of material and settlement of the wall, leading to cracking. This is often seen on corners and extensions.

Other building elements

Structural elements next to brick can also fail and lead to deterioration. For example, timber joists or lintels in a brick wall may rot and decay, causing the brickwork to become unstable. Serious corrosion of structural iron or steel elements can have the same effect, and may even cause brickwork to burst off the wall face.

Original construction defects

Brickwork that was poorly constructed may lead to problems much later in the life of a structure.

Typical defects include:

• poor bonding between walls or with existing masonry where a brick addition has been made
• poor quality bricks used
• poor wall head detailing leading to wet bricks in the upper part of the wall

Regular building maintenance can help you to avoid most of the problems that can affect brickwork. Much of the focus is on keeping the building watertight, and ensuring proper ventilation, as excess moisture speeds up decay.

Proper maintenance has a cost, but it will usually be much less than the price of future repair work. For example, cleaning out rhones, gutters and downpipes each year will cost much less than erecting scaffolding to replace a large area of decayed bricks.

Keeping water out

Your property should be regularly inspected for:

• failures in roofing leadwork, e.g. missing flashings, splits in lead-lined parapet gutters
• blockages and fractures in rainwater goods, e.g. cast iron rhones and downpipes
• failed below ground drainage
• poorly functioning drip details on copes
• condensation – often made worse by the use of modern insulation materials and impermeable paints

All can lead to high volumes of water entering brickwork, which will result in decay. To avoid this risk, frequent maintenance checks should be made and any faults repaired as soon as they’re discovered.

You should also look out for pointing missing between individual bricks. If left open for long periods, moss, grasses, small bushes and saplings will grow in the voids. Lime mortar should be used to repoint any open joints.

Soiling and plant growth

Excessive soiling to bricks may suggest that damage is occurring. But intense biological growth – algae, fungi, lichens and/or bacteria – or salt deposits on masonry is generally just a maintenance problem. For example, many such issues can be resolved by repairing damaged or blocked drainage, or by repointing bricks. Unlike cement mortar, lime mortar lets salts migrate to the surface through joints, avoiding damage to the brick.

A large amount of efflorescence can cause serious damage to bricks. Once the cause is resolved, you can remove the salt deposits using a non-ferrous bristle brush.

Mosses and lichens can also be removed by brushing. Larger plants should be cut away from brickwork. Cut through the stem of a creeper and let it die back. Then remove small sections at a time of the withered plant. You will need to use suitable cutting tools to fully remove any roots that have got into a wall. All open joints must be repointed and any damaged bricks cut out and replaced.

Don’t be tempted to pull a creeper off a wall using a rope: you could cause serious damage to yourself and to the brickwork.

The decision to repair brickwork shouldn’t be made lightly. Only essential repairs should be carried out, as there’s always a danger that work will cause more damage than good in the long run.

For example, a brick that’s lost its ‘fire skin’ (outer surface) through spalling will need to be cut out and replaced. But there’s rarely, if ever, a need to remove nearby bricks that aren’t affected. Replacing more bricks than required may introduce large areas of denser, less permeable replacement brick. Water shed from these areas can then increase the risk of decay in original bricks.

Finding the root cause of damage

Fixing the cause of a defect is the first step in any repair. There is little point in carrying out costly repairs if the same problem will cause further damage in future.

Chemical treatments

Using chemicals to stabilise brick should only be considered with caution. Such treatments may be effective initially, but there’s no way of knowing what effect they may have in the long term. Chemical sealants may be just as good at trapping moisture inside brick as keeping water out.

Assessing the need to replace bricks

Single bricks or small areas of brickwork may sometimes need to be replaced, particularly if spalling has occurred. Great care must be taken not to cause any new damage when cutting out the affected brick.

Bricks can probably be left in place if they have only:

• minor cracks that show no sign of worsening
• spalling that affects less than 20% of the brick’s surface

Sound bricks removed in the process of wider repairs should be set aside for reuse to ensure that as much as possible of the original fabric is kept.

Learn about choosing and sourcing replacement bricks.

Assessing the need to repoint

Areas of mortar will fail at different rates in line with their exposure. An entire building is unlikely to require repointing at the same time. Where a small area of repointing is required, there’s no need even to repoint the entire elevation.

As a rough guide, a joint doesn’t need to be repointed until it’s eroded to a greater depth than its width. For example, a joint 10mm wide that’s eroded 5mm deep needs no work. Exceptions to this rule include where water is coming through the joint or cement pointing is causing severe decay to bricks.

Find out how to make lime mortar repairs.

Brick arch repairs

Almost all brick buildings in Scotland feature arches. Repairing a brick arch can be a complex task requiring a high level of skill. Both the look and stability of the arch rely on the repair matching the original in profile, accuracy, bonding and quality of finish.

Cutting out and replacing a brick may be necessary if it’s so decayed or damaged that it can no longer do its job properly. The process is the same whether it’s a single brick or a section of brickwork to be cut out and replaced.

A chisel with a tungsten tip should be used to carefully tap out the mortar by hand from around the affected brickwork. Care must be taken to avoid damaging the edges of sound bricks next to the work area. With old mortar removed, the bricks to be replaced can be easily lifted out.

A skilled contractor may use a mechanical tool with an oscillating blade to cut out bricks if removing cement mortar from a large area. The blade should be tungsten tipped and smaller than the mortar joint is wide. A vast amount of fine dust is produced, posing a health and safety risk. Disc cutters must never be used on brickwork.

Preparation of the void

The void that’s left must be cleaned of dust and debris before the replacement brick is put in place. All surfaces that the replacement brick will touch should also be dampened, right the way to the back of the void.  

Wetting the existing dry bricks with water stops them from sucking the moisture out of the mortar too quickly. If this is allowed to happen, the mortar will shrink and crack. Some brickwork is very porous and may need to be dampened more than stone masonry would.

Bedding replacement bricks

1. Mortar is applied evenly to the back of the void and to all other surfaces of existing brick that the replacement will touch.
2. To create a bed joint for the replacement brick, a layer of mortar is applied to the upper side of the existing bricks on which it will sit.
3. Mortar is applied to the top and sides of the replacement brick.
4. The brick is inserted into the void without staining nearby brickwork.

How bricks are laid and interlock is crucial to the structural integrity of brickwork – as well as to how it looks. The existing bricklaying pattern should be copied to ‘maintain bond’. 

Finishing joints

Just as with repointing, a narrow bladed pointing trowel or key should be used to push the mortar back firmly into the joint. This action is then repeated until the joint is packed and the mortar is flush with the brickwork.

The new joint can be finished with a joint profile to match that of the existing brickwork.

Replacement bricks should match the originals in:

• brick type
• size   
• colour
• surface texture and finish
• durability  

Bricks can vary greatly in size by type and date of manufacture. To know what size of replacement to use, work out the average size of 12 bricks taken from several rows.

You may be able to source reclaimed or second-hand bricks from salvage yards or other building material suppliers. The seller must tell you where they’ve come from, but you should also inspect bricks closely before buying. Don’t buy any that have been damaged by demolition or careless handling.

All historic bricks were graded for suitability of use: a reclaimed brick meant for internal use is likely to fail if placed in an external wall.

Brick matching services

A number of companies can still make bricks to match your needs. Many offer a brick matching service (colour, surface finish and texture etc). Or you can use a colour stain to tone in new bricks with the existing wall.

For details of suppliers of bricks for repairs to traditional brickwork, contact the Brick Development Association.

Lime mortar must be used to repoint traditional brickwork. Mortar analysis can help to achieve as close a match as possible to the original mortar used.

Ordinary Portland Cement, often suggested as a binder for use in repointing work, is incompatible with traditional brickwork. Historic cement mortar that is now causing decay can be replaced with a lime mortar.

Preparation of the brickwork

Unsound mortar must first be carefully raked out to allow for repointing. This is usually best done with a mortar pick or rake, or other suitable hand tool.

An experienced contractor may instead use a mechanical aid with tungsten-tipped oscillating blades. Used with great care, it can help to remove hard, cement-based mortar in particular.

Joints are usually raked out to a depth of at least 2.5 times their width. For example, a 10mm wide bed joint will be raked out to a depth of 25mm. Further raking out may be called for, however, if the mortar at this depth isn’t sound enough to be used as a base for the new mortar.

The raked-out joint cavity must be cleaned of all dust and debris. A brush or, ideally, a vacuum cleaner should be used for this task.

Both the interior of the joint cavity and the surface of adjacent bricks should be dampened well, but not saturated, with water. This stops the moisture in the mortar from being absorbed too quickly by surrounding dry brickwork. Rapid drying is a problem as it causes mortar to shrink and crack.

Lime mortar shouldn’t be applied in freezing or very cold conditions. The temperature should be at least 5ºC and rising. Alternatively, an enclosed and warmed scaffold can be erected around the brickwork to be repointed.

Applying the mortar

1. A portion of mortar the consistency of modelling clay is placed on the hawk.
2. A small amount of the mortar is tapered into a thin edge the width of the joint to be repointed.
3. This is lifted off the hawk and placed into the cavity using a finger trowel, brick jointer or pointing key that’s the same width as the joint.
4. The mortar is pushed firmly into the cavity to ensure that the joint is filled from the back.

It’s usually best to work outwards from existing sound mortar or from earlier repointing efforts. Mortar should be applied with care to avoid smearing the face of the brickwork. Leave any out-of-place mortar to firm up slightly before removing it. 

Any joint profile applied to the existing brickwork should be copied when repointing. A joint surface finish can be applied after the initial set.

Aftercare

Wind and warm weather can speed up the drying process. Covering repointed brickwork with damp hessian will protect the mortar and allow it to dry at a suitably gradual pace.

Repointing work should also be protected from rain and frost.

You should check whether you must first apply for planning permission or any other type of consent before making any changes to historic brickwork of any kind. Listed building consent or conservation area consent may be needed, depending on the property and its location.

For listed properties, listed building consent may be required before repairs are made to original brickwork.

Contact your planning authority to find out more.

Find out more about listed building consent and conservation area consent.

Brick began to be used in Scotland in a small way in the 1600s, when it was used to construct chimneys, ice houses and garden walls.

It continued to be used for these purposes in the first half of the 18th century. But by this time brick was also finding new, domestic uses in high status buildings, for example, in vaulting and to internally line ashlar walls.

Brick started to be used more often from 1750. Fort George was Scotland’s first large building constructed almost entirely of brick. Stanley Mills, built in 1785, was the first mill in the country to be made of the material. And it was brick that was used to build farm buildings of all sizes and levels of status.

Brick was used extensively in the early 19th century for industrial buildings and increasingly to build housing for mill and factory workers nearby. It continued to be a popular building material in rural areas too.

The ‘golden age’ of brick in Scotland dawned around 1850 and lasted until the start of the 20th century. This was the time when brick was used to its full, glorious effect, with glazed, special and polychromatic brickwork adorning both industrial and domestic buildings.

Brick was used widely in Scotland at this time, across all building types. Engineered structures such as bridges, tunnels, lighthouses and chimneys were all built of brick. Mass production also finally became possible in the late 1800s, allowing brick to be used to create vast areas of housing for industrial workers.

Manufacturing developments

Until the 1840s, all bricks made in Scotland were moulded by hand from clay and fired in relatively small kilns. Large estates might have a small brickworks on site, and architect Robert Adam set up his own commercial concern in Kirkcaldy in 1714.

Huge increases in production were seen in the 1830s, as Scotland unveiled its first mechanised brick moulding machines. It’s estimated that Scotland manufactured just over 15 million bricks in 1802, but this figure had risen to nearly 48 million bricks as soon as 1840.
 
Further advances came in the 1850s, when Scotland’s first continuous kiln began operations, enabling many more bricks to be fired at once. Better manufacturing processes also made for a more consistent product and enabled bricks to be created in more shapes and colours. This led to brick’s golden age, as polychromatic decoration, dogtooth courses and new forms of arches were used to great effect, especially in industrial buildings.

By the 1870s, groundbreaking developments in manufacturing allowed colliery shale to be used as a raw material for brick making. Many coal companies set up brickworks to profit from manufacturing ‘colliery bricks’ out of shale, a waste by-product of coal extraction. And an expanded railway network took bricks from the site of manufacture to wherever they were needed.

Entire villages and towns were built with colliery bricks to house Scotland’s growing industrial workforce. Most buildings were of poor quality and haven’t survived, but some examples – like Newtongrange – can still be seen today.

Get in touch if you have any questions. We will be happy to help.

• Technical Research Team
• 0131 668 8951
• technicalresearch@hes.scot

Professional institutions

Brick Development Association

Publications

Inform guides

An introduction to conservation and maintenance of traditional buildings for complete beginners.

Repairing Brickwork
Terracotta and Faience

Short guides

Information on building conservation topics for home owners, trades people and building professionals.

6 — Scottish Traditional Brickwork

Conference Proceedings

Papers and abstracts from building conservation and archaeology conferences.

Historic Scotland Traditional Building Materials Conference 1997

Other resources

Building Scotland – Celebrating Scotland’s Traditional Building Materials
The Investigation, Repair and Conservation of the Doulton Fountain, Glasgow Green
The Building Conservation Directory