In the history of professional construction practices, brick is one of the oldest of all building materials. It is also arguably the most durable, since there are brick walls, foundations, pillars, and road surfaces constructed thousands of years ago that are still intact.
When asked to think of a brick building, you might conjure up an image of a red brick schoolhouse or a similar traditional structure, but "brick" doesn't refer to a single material. In fact, bricks can be made of many different materials and for different purposes.
Here we'll cover a range of types of brick and the uses of each.
What Is Brick?
Officially, the term "brick" is used to denote a building unit made of shaped clay, but in modern times it refers to any stone- or clay-based building unit that is joined with cementitious mortar when used in construction. Typically, bricks are about 8 inches long, 4 inches wide, and a variety of thicknesses, with variations in different countries. Larger stone- or clay-based building units as used in foundations are called "blocks."
Advantages of Brick Construction
There are many advantages when bricks are used in construction.
- Aesthetic: Bricks offer a variety of natural colors and textures.
- Strength: Bricks offer high compressive strength.
- Porosity: The ability to release and absorb moisture helps regulate temperatures and humidity inside structures.
- Fire protection: When prepared properly, brick can resist fire at maximum protection ratings for up to 8 hours.
- Sound attenuation: The amount of sound a brick wall blocks out varies, but standard forms can block an average of 60-70 decibels, and brick walls can be constructed to block over 200 decibels.
- Insulation: Bricks absorb and release heat slowly for excellent thermal insulation compared to other materials. By helping to regulate and maintain constant interior temperatures of a structure, bricks can save 50% more energy than wood.
- Wear-resistance: Strong composition resists wear and tear that is common in other materials.
Unlike wood, bricks are man-made, requiring no excavation, deforestation, or exploitation of non-renewable resources.
How Bricks Are Made
Bricks can be made in a variety of ways, often from a clay-based material, molded into shape, and then fixed in form with heat or other drying processes.
The oldest bricks used natural clay and were dried in the sun. Over time, techniques were developed to make bricks stronger and more resilient to weight, heat, weather, and erosion. Clay can be mixed with concrete, ash, or various chemicals to change the composition of brick to achieve desired qualities.
How Bricks Are Categorized
There are a number of ways that brick can be categorized. For example, you can divide brick into the types used for "facing" (exposed) vs. "backing" (structural and hidden from view), by how they are manufactured: "unfired" (air-cured) and "fired" (oven-baked), or by use: "common" bricks (used for residential construction) and "engineering" bricks (used in heftier civil projects).
Bricks can be categorized according to different features, but categories overlap and the taxonomy—though very descriptive—is imperfect.
Bricks can also be categorized according to their shape:
- Brick veneers are thin and used for surface cladding.
- Airbricks contain large holes to circulate air and decrease weight for suspended floors and cavity walls.
- Perforated bricks contain many drilled cylindrical holes and are very light in weight.
- Bullnose bricks are molded with round angles.
- Paving bricks contain iron for underfoot paving applications.
- Capping bricks top freestanding walls.
- Hollow bricks are about one-third of the weight of the normal bricks, for non-load-bearing partition walls.
Categorizing Bricks by Raw Materials
In modern construction practices, bricks are categorized according to their component materials and method of manufacture. Under this classification, there are five common types.
Burnt Clay Bricks
Burnt clay bricks are the classic form of brick, created by pressing wet clay into molds, then drying and firing in kilns. This is a very old building material, and found in many of the ancient structures of the world. In appearance, these bricks are solid blocks of hardened clay, usually reddish in color.
Burnt clay bricks are typically sold in four classes, with first-class offering the best quality and most strength. These high-grade burnt clay bricks have no noticeable flaws and naturally cost more than lower classes.
When burnt clay bricks are used in walls, they require plastering or rendering with mortar. Uses for burnt clay bricks include masonry walls, foundations, and columns.
Sand Lime Bricks
Sand lime bricks (also known as calcium silicate bricks) are made by mixing sand, fly ash, and lime. Pigments may also be added for color. The mixture is then molded under pressure to form bricks. Sand lime bricks are not fired in kilns in the same manner as burnt clay bricks; instead, the materials bond together by a chemical reaction that occurs as the wet bricks dry under heat and pressure. Sand lime bricks offer advantages such as:
- Their shape is uniform and presents a smoother finish that doesn’t require plastering.
- They offer excellent strength for load-bearing structures.
- They are gray instead of the regular reddish color. Different pigments can be added for ornamental purposes.
- Less mortar is required during construction.
- Edges are straight and precise, making construction easier.
- They do not effloresce salts and minerals.
Sand lime bricks are most often used in structural foundations and walls, exposed brick and pillars, and, when pigment is added, for ornamental uses.
Engineering bricks are used primarily in civil projects where strength and resilience against the elements are essential. They are clay-based and can be mixed with many other materials. What sets engineering bricks apart from other types is their extreme durability: They are fired at excessively high temperatures to produce a brick as hard as iron. They also have very low porosity and are used in places like sewers, retaining walls, manholes, foundational work, and underground tunnels, where resistance to water and frost is crucial. They come in two classes, A and B, with A offering higher compression strength and lower water absorption for the toughest conditions.
"Fire" or "refractory" bricks are also fired at extremely high temperatures and manufactured from specially formulated earth with a high aluminum oxide content in order to withstand incredible heat for use in places like chimneys, barbecues, and pizza ovens.
Concrete bricks are made from solid concrete poured into molds. They are traditionally used in internal brickwork, but are more frequently being used in exterior work, such as facades and fences, to provide a modern or urban aesthetic. Concrete bricks can be manufactured in different colors if pigments are added during production.
Due to their durability, concrete bricks can be used in almost any type of construction, except underground, since they tend to be porous.
Fly Ash Clay Bricks
Fly ash clay bricks are manufactured with clay and fly ash—a byproduct of coal burning—fired at about 1,832°F. This type of brick is sometimes described as self-cementing, since it contains a high volume of calcium oxide and therefore expands when exposed to moisture. This tendency to expand, however, can also produce pop-out failure. Fly ash clay brick has the advantage of being lighter in weight than clay or concrete brick.
Typical uses for fly ash clay brick include:
- Structural walls
- Anywhere that improved fire resistance is required
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