fired clay brick
cladding: MATERIALS ENCYcLOPEDIA
Applications for this system
Exterior and interior structural wall
May be small amounts of lime, iron oxide and/or magnesia
Mortar of clay/sand, lime/sand, or lime/cement/sand
Ratings Chart for Fired Clay Brick cladding
The ratings chart shows comparative performance in each criteria category. Click on the tabs below for detailed analysis of each criteria.
- HOW THE SYSTEM WORKS
- ENVIRONMENTAL IMPACTS
- EMBODIED CARBON
- ENERGY EFFICIENCY
- MATERIAL COSTS
- LABOUR INPUT
- SKILL LEVEL REQUIRED
- SOURCING & AVAILABILITY
- CODE COMPLIANCE
- INDOOR AIR QUALITY
- FUTURE DEVELOPMENT
Fired clay brick System
Bricks of a typically rectangular shape are cast from a mixture of clay, sand and small amounts of admixture and fired in a kiln at temperatures between 700 and 1100 ∞C (1300 and 2000 ∞F). This heating takes the clay through several stages, including the burn-off of carbon and sulfur, driving off chemically combined water from the clay, quartz inversion, sintering and vitrification. At the end of this firing process, the clay brick is hard and will not soften when it reacts with water.
Bricks are laid in successive courses, bonded by a mortar of clay/sand, lime/sand or lime/cement/sand. There are many different patterns for brickwork, but most feature offset joints between courses. Keystone arches can be formed to create self-supporting openings, or metal reinforcement is used to form straight openings.
When used as cladding, bricks are attached to the structural sheathing by means of metal ties that are nailed to the wall and embedded in the mortar joint, and a space is left between the brick and the sheathing to create a rainscreen. Weeper holes are left at intervals in the top and bottom courses to allow moisture to escape.
When used structurally, brick walls are typically one part of a double masonry wall, with an insulated core between the two wythes. Ties are placed at intervals between the two walls to increase stability. Structural brick walls are also built using a doublewide arrangement of bricks. It is rare for fired clay bricks to be used structurally in modern construction in North America.
Not Cement Brick
Many brick products on the market are actually cement-based and not clay. There are many resources available to make comparisons between cement and clay brick. Cement brick manufacturers often claim that they are “greener” than fired clay because making them doesn’t require heat. This, however, ignores the high heat input (and significantly higher carbon release) required to make the cement.
A case can be made for the use of cement brick as a green building product, largely based on its durability. It is not included in this book because of its high carbon footprint and low permeability, and because it is an intensive material to be used non-structurally as a cladding.
Environmental Impact Rating
Harvesting — Low to moderate
The clay that forms the bulk of the material in a brick is an abundant resource, with useful deposits in many regions of North America. Clay pits are usually shallow, surface-based harvesting operations that do not use any chemical processes on-site. Disruption to flora and fauna in the immediate region of the pit will be palpable. Many clay pits are in or beside waterways, and pit operations can cause silting of the water and disruptions to flow patterns. In general, clay pits are not considered high-impact mining operations, and are excellent candidates for rehabilitation at the end of their lifespans.
Manufacturing — High
Clay for bricks requires some mechanical processing. It is ground up and squeezed into a homogeneous mix before being formed. This work is typically all completed by machine in factories, though traditionally it would have been done by hand on or near the building site. The largest impact comes from the firing process, during which the bricks are heated to temperatures of 900 to 1300 °C (1650 to 2350 °F) for several hours. No toxins are released from the clay during this process, but a lot of fossil fuels are consumed and emissions released into the atmosphere, including sulfur dioxide.
Bricks that are glazed or painted will require additional processes, and these can be more toxic. Paint coatings, in particular, can contain chemicals that are emitted into the atmosphere and/or mixed into water at the factory.
The mortar used between bricks is a significant amount of material. If a cement-based mortar is used, it carries a high carbon footprint. Lime-based mortars have a lower carbon footprint.
Transportation — Low to High
Sample building uses 26,192 kg of brick siding for the exterior:
24.6 MJ per km by 35 ton truck
6.55 MJ per km by rail
Production facilities are typically very close to clay pits, minimizing the transportation of raw materials. Regional manufacturers are close to many major markets, but if this heavy material has to travel long distances it will accumulate high transportation impacts.
Installation — Negligible
Compostable — Clay brick offcuts can be left in the environment or used as aggregate or growing medium. Quantities should be low, as partial bricks can be used throughout the wall.
Recyclable — None.
Landfill — Mortar bags.
Chart of Embodied energy & carbon
Brick cladding will not have much impact on energy efficiency. As a rainscreen, it can reduce the amount of wind that reaches the wall behind, but will not contribute to air tightness. Bricks add little to no thermal resistance.
Bricks can be used to create thermal mass inside a building. This will not improve energy efficiency, but may help to modulate temperature swings inside the building, improving comfort. Brick walls are sometimes used as part of a hydronic heating system.
Material costs: high
Labour Input: High
Laying brick is very labor-intensive. Each unit is relatively small and requires careful mortar joints on all sides. The material is heavy; mortar is prepared in small batches and must be kept fresh. Brick ties, weepers and headers over windows all add to the labor input. If patterns and/or arches are included in the design, labor input rises further.
Mortar mixing can cause exposure to high quantities of silica dust, so proper breathing protection is required.
Skill level required for homeowners
Preparation of substrate — Easy
Wall framing and sheathing skills are required. The process of measuring and fastening brick ties is straightforward.
Installation of sheathing — Moderate to Difficult
There is a lot to learn in order to successfully install brick cladding. Skills required include marking and measuring for brick courses, mortar mixing, laying mortar and brick and creating appropriate headers/arches for openings. Without prior experience or practice, brick laying may best be left to professionals.
Finishing of sheathing — Easy
Jointing between the bricks is the only finish required once bricks are installed.
Sourcing & availability: Easy
Clay bricks are widely available in most regions from masonry supply outlets.
Clay bricks provide a very durable cladding that can last for at least a hundred years, and possibly several centuries. Proper window flashings and an adequate protection from roof splashback will help ensure long life. Bricks that repeatedly absorb a lot of moisture and then freeze (the freeze-thaw cycle) will deteriorate within a decade.
Interior applications of clay brick will be extremely durable.
Acceptable solution in all codes. Be sure to follow local codes for specific requirements.
Indoor air quality: n/a
No effect as an exterior cladding.
Interior brick walls should not have a negative impact on IAQ. If using recycled brick, be sure to assess the origin of the brick before using them indoors as they may have been used on a building or in a location where the porous clay may have absorbed toxic materials (e.g., old chimney brick, kiln brick or industrial brick).
Resources for further research
BDA Guide to Successful Brickwork, 3rd Edition. London: Arnold, 2000. Print.
Hendry, A. W., and F. M. Khalaf. Masonry Wall Construction. London: Spon, 2001. Print.
Kelsey, John. Masonry: The DIY Guide to Working with Concrete, Brick, Block, and Stone. East Petersburg, PA: Fox Chapel, 2012. Print.
It is unlikely that techniques or materials for brick manufacturing will change dramatically. Brick has a long history in building, and will likely continue to have a reasonable portion of the cladding market. Brick is widely perceived to be an “upscale” cladding, used to distinguish a quality home from a cheap home. Rising costs for brick and masons may cause the market to shrink.
Tips for successful Clay brick cladding
1. Building science has brought a good understanding of the porous nature of fired clay brick, which can store large quantities of water during rainfall events, and has reinforced the need for ensuring a properly ventilated air space between brick and wall sheathing.
2. Brick cladding must be designed into the project from the start, as it will require a brick ledge on the foundation and proper detailing for doors, windows and flashing to suit the thickness of the wall and to bridge the air gap between the wall and the brick.
3. There are many excellent resources available to assist in the successful installation of brick cladding. Be sure to seek proper advice and instruction.
4. Clay brick can make an attractive interior wall or wainscoting. For some interior applications, it may be load-bearing and/or self-supporting.