Brick is a remarkably versatile building material with a rich history spanning thousands of years. It is celebrated for its inherent durability and high compressive strength, making it an excellent choice for a wide array of construction and civil engineering projects. Bricks are extensively utilized as structural elements in buildings, tunnels, bridges, and various types of walls, as well as for functional and aesthetic applications like floors, archways, chimneys, fireplaces, patios, or sidewalks. Beyond its robust mechanical properties, brick is also highly valued for its distinctive aesthetic appeal, which has made it a consistently popular choice in architectural design.
Historically, many of the earliest forms of brick were unburnt bricks, which were dried naturally using the sun’s light; these are also known as sun-dried bricks. While historically significant, they generally possess lower strength and are, therefore, not employed in modern, demanding construction and civil engineering applications.
This article provides a comprehensive review of common brick types, examining their material formulations, fabrication methods, and intended uses. Additionally, it highlights the significant advantages of brick compared to alternative building materials and discusses some of its key physical properties.
Brick Characteristics
Brick can also be categorized by its intended visibility in the final structure. Facing brick—commonly referred to as face brick—is designed such that its front surface remains exposed and visible in the finished construction. For face brick, the aesthetic appearance of the surface is paramount, often necessitating a more expensive grade of brick with minimal or no defects, and featuring a desired texture or design style. Conversely, backing brick does not have a visible face and is used purely for structural support, typically concealed behind the face brick or other finishes.
While many bricks are solid units, there are also specialized forms like perforated bricks and hollow bricks (also known as cavity bricks). Both perforated and hollow bricks are lightweight, require less raw material for their fabrication, and are frequently used in non-load-bearing applications where reduced weight is an advantage.
Advantages of Bricks
In various construction applications, bricks offer several distinct advantages over alternative materials that serve similar purposes:
- Exceptional Durability: Brick is an incredibly durable material, capable of lasting for hundreds or even thousands of years if properly maintained.
- Fireproof: Brick is inherently fireproof and can effectively withstand prolonged exposure to high temperatures, providing crucial fire protection.
- Noise Reduction and Sound Isolation: Brick offers excellent noise reduction and sound isolation capabilities, contributing to quieter interior environments.
- Low Maintenance: Brick generally does not require the application of paints or other protective finishes, as it is inherently resistant to environmental degradation.
- Modular Component: As a modular building component, issues with individual bricks (e.g., damage) can often be addressed or repaired without the need to demolish and rebuild the entire structure.
- Local Sourcing and Cost-Effectiveness: Since clay, the primary raw material for many bricks, is available in almost every region, bricks can often be fabricated locally. This eliminates significant costs associated with long-distance shipment, potentially making construction with brick less expensive than using materials like stone, concrete, or steel.
- Ease of Workability: Brick is simpler to work with due to its inherent uniformity in size, unlike natural stone which often requires laborious sizing and dressing.
- Readily Available Skilled Labor: Bricks are easy to handle, and skilled tradespeople proficient in bricklaying are generally plentiful, simplifying the construction process.
Types of Brick by Material
There are several methods for classifying or characterizing brick. In the sections below, bricks are primarily characterized by the material composition used in their manufacturing process.
Types of Bricks Used in Construction
Burnt Clay Brick
One of the most common types of bricks used in construction are those based on clay as the primary material. These include burnt clay brick and fire clay brick, often collectively referred to as common brick.
Burnt clay brick is produced from clay that is either molded, dry-pressed, or extruded into shape, and subsequently dried and fired in a kiln at high temperatures. This type of brick is further classified into different grades—first, second, third, and fourth class—which relate not only to their appearance but also directly to their porosity and compressive strength.
Table 1 below summarizes the properties of the different classes of burnt clay brick:
Table 1 – Classes of Burnt Clay Brick and Their Properties
| Class | Appearance | Compressive Strength | Absorption* | Uses |
| First | Thoroughly burnt, square edges, parallel faces, free from chips, cracks, and flaws | > 1,990 psi (140 kg/cm²) | <20% | Exterior walls, flooring |
| Second | Slight irregularities in shape, color, or size | >996 psi (70 kg/cm²) | <22% | Exterior use with plastering (rendering) |
| Third | Less fully burnt, noticeable defects in shape or uniformity | 498 – 996 psi (35 -70 kg/cm²) | 22% – 25% | Temporary construction in dry conditions |
| Fourth | Irregular in shape, darkly colored due to overburning | >2134 psi (150 kg/cm²) | low | Used in broken form as aggregate in road construction, foundations |
*Absorption measured after immersion in water for 24 hours.
Data compiled from reference source 6.
Fly Ash Brick
Fly ash brick, also known as fly ash clay brick, is manufactured from a mixture of fly ash (a glassy particulate byproduct from burning pulverized coal in power generation facilities) and clay, fired at extremely high temperatures. The incorporation of fly ash results in bricks with higher concentrations of calcium oxide, which makes them less porous and exhibit lower levels of water penetration. These bricks also possess self-cementing properties, forming stronger bonds during the curing process. Compared to traditional clay bricks, fly ash bricks generally have a higher density, demonstrate improved ability to withstand freeze-thaw cycles, and exhibit excellent fire isolation properties. Their reduced porosity also translates to enhanced resistance and lower water absorption, significantly boosting their durability across various construction applications.
Fire Brick
Fire brick, commonly referred to as refractory brick, is a specialized type of brick constructed from fire clay. Fire clay is characterized by a very high melting temperature (approximately 1600°C or 2912°F) due to its elevated alumina content, which typically ranges from 24% to 34%. These bricks are specifically engineered to possess high-temperature tolerance, low thermal conductivity, and the critical ability to withstand repeated thermal cycling and rapid temperature changes without degradation. Fire bricks are commonly used in applications directly exposed to extreme heat, such as the lining of furnaces, kilns, chimneys, fireplaces, and industrial boilers. They are also integral in lining wood-fired ovens and in providing crucial thermal insulation to improve the overall energy efficiency of high-heat devices. Magnesite brick, composed of more than 90% magnesium oxide, is one notable example of a fire brick.
Sand Lime Brick
Sand lime brick, also known as calcium silicate bricks or flint lime bricks, is manufactured from a mixture primarily consisting of sand, lime, and water. A pigment is frequently added to the mix to produce bricks in various colors, as they would otherwise appear grey or off-white. Common pigments and their corresponding colors are shown below in Table 2:
Table 2 – Common Pigments of Sand Lime Bricks
| Pigment | Color |
| Carbon Black | Black, Grey |
| Chromium Oxide | Green |
| Iron Oxide | Red, Brown |
| Ochre | Yellow |
In contrast to fired bricks, sand lime bricks are chemically set bricks. This means their curing process is accomplished by using heat and pressure in an autoclave, which accelerates the chemical reactions essential for their hardening.
Sand lime bricks offer several advantages over traditional fired clay bricks:
- Superior Load-Bearing Capability: They possess a very high compressive strength (typically 1450 psi or 10N/mm²), indicating excellent load-bearing capacity.
- Uniform Appearance: These bricks exhibit a consistent color and texture, providing a cohesive aesthetic.
- Smooth Finish: Their smooth finish often requires less plastering when used on a visible surface, saving labor and material.
- Good Acoustic Insulation: They offer effective sound insulation properties.
- Good Fire Resistance: They demonstrate commendable resistance to fire.
However, sand-lime bricks do have some disadvantages when compared to their clay counterparts. One notable issue is thermal movement: sand-lime bricks tend to shrink slightly after being laid, whereas clay bricks tend to expand over time. If this shrinkage is not adequately accounted for during the design and construction phases, it can lead to cracking in the structure. Additionally, sand-lime bricks generally exhibit low abrasion resistance, which renders them unsuitable for use in demanding paving applications where surface wear is a concern.
Concrete Bricks
Concrete bricks are fundamentally composed of Portland cement, water, and various aggregates.
Concrete bricks are created by pouring the concrete mixture into a mold to cast a uniformly-sized brick product. The molds can be specifically designed to produce a variety of finishes on the face edge of the brick to suit desired architectural details and aesthetics. These finishes might be smooth, or they may simulate the look and texture of natural stone, for example. Various pigments can be added to the concrete mixture during manufacturing to achieve a wide range of different colors and appearances. Pigments such as iron oxide can be added solely to the surface layer or thoroughly mixed throughout the concrete to generate different visual effects for the brick. The texture of the brick can also vary significantly based on the type of aggregate used, ranging from coarse stone particles to fine sand.
A significant difference in strength is apparent when comparing concrete bricks to clay bricks: clay bricks are typically around 2.5 to 3 times stronger than concrete bricks. The average compressive strength of concrete bricks generally falls somewhere between 3,000 – 4,000 psi, while well-fired (hard) clay bricks exhibit a much higher average compressive strength of 8,000 – 10,000 psi. Concrete bricks are also more absorbent than clay bricks. The Initial Rate of Absorption (IRA) for clay brick is approximately 15 to 35 grams of moisture per minute over a 30-square-inch surface. In contrast, concrete brick typically exhibits absorbency values that are some 2 to 3 times higher, approximately 40 – 80 grams per minute across the same surface area.
Concrete bricks are often differentiated from concrete blocks, also known as Concrete Masonry Units (CMUs), primarily based on size. Concrete bricks are typically smaller and solid, whereas CMUs are generally larger and frequently incorporate hollow cavities. However, this distinction is not always applied consistently across the industry, as different suppliers may sometimes use these terms interchangeably.
Engineering Bricks
Engineering bricks are specifically designed and manufactured to provide exceptionally high compressive strength and very low porosity. These characteristics make them an ideal choice for construction projects where material strength and superior resistance to water and frost are paramount considerations. They are routinely used in construction applications where the overall structural integrity of the material, along with its ability to resist water penetration and frost damage, are critical factors.
There are two distinct classes of engineering brick, each possessing different strength and porosity specifications. Table 3 below summarizes the properties for each of these classes:
Table 3 – Properties of Engineering Brick
| Brick Class | Compressive Strength | Porosity |
| Class A | 125 N/mm² (18,130 psi) | <4.5% |
| Class B | 75 N/mm² (10,878 psi) | <7% |
Because of their superior ability to resist water penetration and frost damage, engineering bricks are commonly employed in demanding locations exposed to moisture and extreme weather conditions where aesthetic considerations are less important. Typical applications include tunnels, sewers, manholes, and various other below-ground structures.
Relevant ASTM Specifications for Brick
Several ASTM (American Society for Testing and Materials) specifications are crucial for the proper use and testing of brick in construction, particularly for solid masonry units fabricated from clay or shale. These widely recognized standards ensure that bricks meet specific quality and performance criteria, tailored to their intended application. These ASTM standards are available for purchase at https://www.astm.org/.
- ASTM C62 – 17 – Standard Specification for Building Brick (Solid Masonry Units Made From Clay or Shale): This standard covers bricks primarily used for structural and non-structural applications where the visual appearance of the brick is not a critical factor. This includes bricks selected predominantly for their fundamental physical properties, such as compressive strength and durability.
- ASTM C216 – Specification for Facing Brick (Solid Masonry Units Made From Clay or Shale): This specification specifically applies to bricks that are intended to be exposed to view in finished construction, such as on building facades. These bricks undergo rigorous testing for aesthetic qualities, including consistency of color, desired texture, and uniformity of appearance, in addition to their essential structural properties.
- ASTM C67 – Test Methods for Sampling and Testing Brick and Structural Clay Tile: This comprehensive standard describes various test methods used to evaluate key brick properties. These tests include assessing modulus of rupture (flexural strength), compressive strength, water absorption rates, saturation coefficient (a measure of durability under freeze-thaw conditions), and overall durability when subjected to freeze-thaw cycles. Additional specialized tests specific to glazed bricks, such as imperviousness and resistance to crazing (fine cracks), are also covered within this standard.
Summary
This article has provided a concise summary of the various types of bricks commonly utilized in construction and civil engineering projects. For information on other related products, readers are encouraged to consult additional guides or visit the Thomas Supplier Discovery Platform to locate potential sources of supply or view detailed information on specific products.