You probably see brick on a daily basis, whether it’s structuring a building, paving the road, or perhaps serving as a fireplace or chimney. But do all these applications use the same type of brick? How are the bricks supporting or being supported? What are these bricks actually made of? Brick’s versatility and ubiquitous nature mean there’s more than one answer to these questions. Even among brick’s most common applications as a building facade and/or structural wall material, there are a variety of types and construction methods employed.
What is commonly referred to as “face brick” is the brick that you see on many buildings - brick that’s not only structural but aesthetic as well, with materials, colors, and textures chosen for the desired design effect [1]. Most face brick is made of clay and fired in a kiln, with the exact ingredients including silica (sand) and alumina (clay), as well as smaller amounts of lime, iron oxide, and manganese. Fired clay bricks can be pressed or molded with a hydraulic press or extruded through a die to achieve the desired shape and size before they’re put into the kiln, which dries out the bricks at high temperatures and gives them their trademark durability.
Inside the kiln, the clay actually undergoes a melting process, which allows the bricks to become hard and solid with low absorption properties [9]. When the clay first begins to melt, it's referred to as incipient fusion because the clay particles become soft enough to bond together when cooled. Next is vitrification, when the bricks become tight, solid, and nonabsorbent. At this point, bricks can optionally be "flashed" to produce color variations, and then are cooled.
Concrete masonry units (CMU) are bricks formed from concrete, which are made of a dry, small aggregate concrete that is vibrated and compacted into molds and then cured using low-pressure steam. Available in multiple sizes and colors, they can be made to simulate the appearance of clay bricks. Concrete bricks will contract, however, and therefore require movement joints in their assembly, but have similar thermal, sound, and fire resistance to other bricks of similar density [2].
Another option is brick composed of calcium silicate rather than clay, which are also referred to as sandlime or flintlime bricks, depending on their exact material composition. These chemically set bricks rely on chemical reactions between these ingredients for hardening rather than the heat of a kiln. The resulting bricks are precise and uniform and can be made in multiple colors. Calcium silicate bricks are more prone to shrinkage than clay bricks and can, therefore, be more susceptible to cracking [2], as well as being less resistant to both abrasion and fire when compared to their clay counterparts [3,4].
Clay bricks’ natural fire resistance is one of the qualities that makes them desirable as a construction material. Building codes and local ordinances require major building components (walls, floors, roofs) to have a certain amount of resistance to fire to protect occupants and give them time to escape if necessary. Elements and assemblies are given a fire resistance rating, a duration of time (not exceeding 4 hours) during which they are able to either confine a fire, maintain their structural integrity, or both [7]. As clay bricks are made in a fire kiln, they’re already highly resistant to fire and can achieve a rating of up to 4 hours depending on the particulars of the wall assembly [8].
Another benefit to working with clay brick is the expansive design variety available. If you’re picturing a classic red-brick building, that’s a start - but it’s certainly not your only option. Clay brick manufacturing companies like Endicott often stock a wide variety of products, including different brick shapes, sizes, colors, and textures. For example, their clay face brick is available in a combination of over thirty colors, eight textures, and sixteen sizes.
Another product offered by Endicott is called thin brick, or what is sometimes referred to as brick veneer. The thin brick has nearly as many color, texture, and size options as the full face bricks, comes in three different thicknesses (½”, ⅝” or 1”), and can offer even greater versatility in certain situations [5].
Thin fired clay units, or thin bricks, are made from the same materials and via similar processes as traditional masonry, yet as the name suggests, the bricks are thinner and weigh less than other clay bricks. First developed in the 1950s, thin brick has gained popularity for combining a traditional masonry aesthetic with the economical savings of a thinner wall section. Thin brick can be utilized in new or existing, residential or commercial structures, even in situations where traditional masonry wouldn’t be possible [6].
The different types of thin brick can be classified by four basic installation methods: thin set, thick set, modular panel systems, and prefabricated panels. Thin and thick set both involve field installation of individual thin bricks into a substrate - thick set uses a thick mortar bed, while thin set can be a thin layer of modified mortar or adhesive. Thin bricks can even be extruded with grooves or dovetails on the back that helps them lock to the substrate, in contrast to "soaps" which are created when a full brick is simply sawed off. Soaps are less desirable in this aspect because the back is smooth and therefore has no innate mechanism for locking to the substrate. Modular panel systems employ an intermediary panel (of polystyrene, metal, or other materials) between the bricks and the substrate wall to assist in supporting the thin brick. Lastly, prefabricated panels are larger, structurally-independent panels that are lifted into place on the building [6].
These thin brick veneer systems can be installed where support for heavier masonry is too difficult. Thin brick systems impart less load on a building, meaning some structural costs may also be decreased. When compared to other lightweight exterior cladding systems, thin brick has better resistance to noise, minor impacts, abuse, heat, and vandalism. Due to the combined mass of the system, it’s able to retain the durability, fire resistance, and acoustic comfort users are accustomed to with traditional clay bricks.
The fire resistance rating of a wall depends on the overall wall assembly rather than individual materials, but common assemblies for metal stud walls with brick veneer are considered to have a 4-hour rating on the brick side, similar to a traditional masonry wall. Many different brick veneer assemblies have been tested and certified to have ratings of 1-2 hours as a whole, even with wood studs instead of steel, which is a sufficient rating for almost all common building types [7].
While maintaining the necessary fire rating and desirable aesthetic qualities of traditional clay brick walls, thin brick is a lightweight, economical, time-saving option to achieve your design goals. Though the term “veneer” can carry connotations of “fake” materials, thin bricks are real clay bricks, simply thinner and installed in different methods than traditional masonry. These installation methods can save time and increase precision on a project, without sacrificing aesthetics or leaving a finished product with a monotonous “prefabricated” appearance. The different sizes and thicknesses with the variety of textures and colors available instead create an inspiring palette for any design.
[1] https://www.merriam-webster.com/dictionary/face%20brick
[2] https://www.sciencedirect.com/topics/engineering/calcium-silicate
[3] https://theconstructor.org/building/calcium-silicate-bricks-masonry-construction/17256/
[4] http://buildingdefectanalysis.co.uk/masonry-defects/an-introduction-to-calcium-silicate-bricks/
[5] https://endicott.com/
[6] http://www.gobrick.com/docs/default-source/read-research-documents/technicalnotes/28c-thin-brick-veneer.pdf
[7] http://www.gobrick.com/docs/default-source/read-research-documents/technicalnotes/16-fire-resistance-of-brick-masonry.pdf
[8] https://home.howstuffworks.com/home-improvement/construction/materials/5-fire-resistant-building-materials5.htm
[9] https://www.gobrick.com/docs/default-source/read-research-documents/technicalnotes/9-manufacturing-of-brick.pdf?sfvrsn=0
