A Brief History of Brickwork
The Properties of Brick
Typically bricks are stacked together or laid as brickwork using various kinds of mortar and bonds to hold the bricks together. They are typically produced in standard sizes in bulk quantities and are one of the longest lasting and robust building materials used throughout history.
A brick is essentially a weight-bearing building unit, laid in horizontal courses with mortar. In essence, they are made from dried earth, usually from clay-bearing subsoil. In some cases, such as adobe, the brick is merely dried. More commonly however, the brick will have been fired in a kiln of some sort at temperatures ranging from 800-1300 degrees celsius to form a ceramic. This gives the brick the properties of being more water resistant, durable and stable than its non-fired counterparts.
Modem continuous firing kilns, are now used to mass produce high quality, uniform bricks. However, this uniformity does not match brickwork of an historic building which with the imperfections of both forming and process provides warmth and character to the architecture.
Different brick types and colours are produced by varying material source, composition and firing.
Calcium Silicate bricks:
These are manufactured from sand-lime (calcium silicate). The bricks are pressed and steamed in an autoclave resulting in a smooth, fine textured and lightly coloured brick. Production dates back to circa 1900. Particular brick colours were obtained from material source, composition and firing temperature.
For ease of handling and efficiency, bricks are designed to be small enough and light enough to be picked up by the bricklayer using one hand while leaving the other hand free for the trowel. The size of bricks over time has changed considerably. Modem bricks are typically 215mm by 102.5mm by 65mm. Because of the variation of historic brick sizes, bricks may need to be custom made for a conservation project.
The properties of a brickwork wall change according to the type of bond chosen for its construction. The common masonry bond types shown below each vary in appearance and strength according to the various configurations of the brick. Loads are distributed in differing ways, walls vary in thickness giving sound and heat insulative variations and surface appearance is changed.
Repair and Conservation Methods
Common defects found in historical brickwork include the following:
• Disintegration of bricks
• Loose brickwork
• Inappropriate mortar
• Damage from removal of renders/paints
• Bulging brickwork
• Spalling of surface (flaking or chipping)
• Cracks through joints
• Cracks through bricks
• Open joints or loose mortar in pointing
• Arrises (edges) broken and surfaces damaged
Replacement bricks should match in colour, texture and size. Reclaimed bricks are commonly used which can be obtained through salvage yards. Replacement bricks must have been weathered or could rapidly fail. Reversing bricks can also be done but is not always possible as the brick could be defective, e.g. underfired.
Brickwork should not be stained to match existing brick as the stain fades at a different rate and becomes apparent. Natural weathering of the brick is preferred. However, mud or soot can be applied to bricks and mortar joints and brushed off.
3. Plastic repairs
Often badly applied on brickwork, naturally pigmented sand with cement if skilfully applied can be successful. Artificial pigments wash out. Brick dusts and epoxy resins, can be used in cracks but not for surface repairs. Generally plastic repairs should be avoided.
4. Bulges and fractures:
The Structural Engineer decides the course of action in this event. Options are to leave alone if not severe enough, or to cut out and repoint the affected area.
5. Stitch and grout
This is a method to prevent movement and is achieved with stainless steel ties, stainless steel bed joint reinforcement and reinforced concrete precast units laid in sections behind brickwork.
Brick masonry can be damaged by inappropriate cleaning methods. Soaking causes efflorescence and damp penetration.
Specialist pulsing methods using air, powder and a little water (the Jos system) reduce the saturation. Dry high-pressure abrasive cleaning systems can be used also. Both systems can cause damage if not carefully executed.
Hydrofluoric acids can be applied and washed off but can still cause damage if not washed properly. Staining of mortars can also occur with this method.
Laser cleaning is a state of the art method of cleaning off soot, smoke, graffiti, biological stains. A monochromatic light is directed from high power lasers to the surface. The beam delaminates the brickwork from any discolouration.
A mortar joint needs repointing once it has weathered to the point where water becomes lodged and may accelerate decay of the brickwork. It is the most common conservation technique with regards to brickwork. Cement repointing should only be removed where it can be removed without damage to surrounding bricks.
Traditional mortars are made from nonhydraulic lime and fine aggregate. These mortars allow for a breathable and porous joint consistent with a traditional soft brick.
Mortars should not be stronger than the brick but strong enough to resist weathering. Pozzolanas can be added to speed up the setting time. Hydraulic lime and white cement can also be used.
Controlled Decay Mortar pointing should be designed and specified to decay slightly quicker than the bricks. The ideal properties are a balance of optimum; flexibility, colour strength, hardness, porosity, and texture.
Causes of pointing failure include:
• Weathering and decay
• Minute seasonal and thermal (changes causing structural movement and cracks)
• Vegetation taking root
• Mason bees (burrowing into soft mortars creating cavities)
• Bad remedial treatment (most common)
Traditional pointing finishes are illustrated below:
Although there are no set rules that can be applied as a ‘one size fits all’ answer to building conservation, there are agreed ethics and principles that are internationally recognised. These principles arose as a reaction to over enthusiastic ‘restorations’ of buildings in the Victorian period which had destroyed a lot of historical buildings eg; the unrecognisable ‘restoration’ of St. Alban’s Cathedral.
Nowadays, every technical decision and intervention should be able to stand up against these criteria:
• Authenticity – genuine, not an imitation
• Integrity – whole or sound in construction
• Avoidance of conjecture –avoidance of ‘re-imagining’ with incomplete information
• Inseparable bond with setting – sensitive to local area
• Respect for all contributions – building should show how the use of the structure has responded to social, cultural and economic change over time
• Rights for the indigenous community – local people should be consulted
• Respect for age and patina – not cleaning to restore to original state
• Minimal intervention – doing as little as possible and as much as necessary
• Like for like materials –using similar materials where available
• Conserve as found / retention of original fabric – repairing rather than replacing
• Reversibility – changes should be reversible where possible
• Documentation – any changes should be clearly documented
• Legibility – any repairs or changes should be distinguishable from original fabric
• Sustainablity – materials should be locally sourced, recycled or re-used from salvage yards where possible.
William Morris and John Ruskin both spoke out in support of conservation:
“These buildings do not belong to us only… they belong to our forefathers and they will belong to our descendants unless we play them false.”
“Restoration so called, is the worst manner of destruction… Do not let us talk then of restoration. The thing is a lie from beginning to end!”
According to the RIAI:
“Intervention may be defined as any act that alters, intrudes upon or interferes with the spatial qualities, fabric, architectural features or setting of a building. Interventions may be described as essential or non-essential and reversible or irreversible. The degree or level to which an intervention can be considered acceptable will depend on the particular merits and characteristics of the individual building…” RIAI
“The intention should be to restrict all interventions to the minimum that is consistent with the established philosophy and the appropriate use, reuse, and continued survival of the building. The philosophy of doing ‘as little as possible and as much as necessary’ applies here.”
Interventions selected, based upon ethical concepts and principles should be defensible and should in theory lead to naturally ‘good’, well founded conservation interventions. A balance should always be sought between competing approaches, principles and ethics
Taking the philosophical issues surrounding repair and conservation into account, it would appear that some of the conservation methods that are employed on brickwork are not in keeping with the accepted conservation principles and should only be used where absolutely necessary.
Firstly, the cleaning of brickwork would be a controversial issue as one would be removing the patina and the aesthetics of ageing of the structure. By doing this you are going down the route of restoration rather than conservation. Also, in the majority of cases this would not come under the principle of ‘minimal intervention’ as cleaning is not fundamental to the preservation of the building.
Another questionable intervention would be the imitation of patina that can be acquired through soot and mud. This is going against a number of ethics and principles in that the patina is not authentic and the intervention would not be legible but instead would blend in with the rest of the building, leaving question marks over what has been repaired or replaced.
Brick in itself seems to be an excellent material to withstand the passage of time once preventative maintenance work is done periodically. More specifically, repointing and crack repair.