During a recent deep dive into recommended animated adaptations of common fables on YouTube, I observed a consistent detail across various versions of The Three Little Pigs beyond just the fundamental storyline: in each rendition, the third little pig invariably opted for red bricks to construct his house!
Yet, as another animated example vividly illustrates (from TJ Toys and Games), bricks are not exclusively red. Even though bricks have been utilized as a building material for thousands of years, many homeowners exploring alternatives to vinyl siding are often surprised by the wide array of brick types available, not all of which are made from clay.
If a brick is defined neither by a reddish hue nor by being composed of clay, what, then, is a brick?
The Evolving Definition of a Brick
Traditionally, the term “brick” referred to a small unit of building material consisting primarily of compacted clay. The specific mineral content within the clay would naturally dictate the brick’s color—clays rich in iron oxide would yield reddish tones, while those containing significant amounts of lime would produce a white or yellowish hue.
In contemporary times, the definition of a brick has expanded to encompass any small rectangular building unit that is joined to other units via cementitious mortar. (Larger building units, conversely, are typically referred to as “blocks.”) While clay remains one of the primary materials for bricks, other commonly used materials now include sand and lime, concrete, and fly ash.
Let’s explore some of these diverse brick types:
Sand Lime Bricks
Also popularly known as calcium silicate bricks, sand lime bricks are characterized by their high sand content, typically ranging from 88% to 92%. The remaining 8% to 12% is predominantly lime. Unlike traditional clay bricks, which undergo a firing process in kilns, sand lime bricks are formed when their constituent materials chemically bond together as the wet bricks dry under specific conditions of heat and pressure.
Compared to other brick types, sand lime bricks offer greater uniformity in color and texture, and their precise edges often require less mortar for bonding. However, a significant limitation is their lower resistance to prolonged exposure to water and fire, rendering them unsuitable for applications such as laying foundations or constructing furnaces.
Concrete Bricks
Concrete bricks offer considerably more versatility in terms of design options compared to traditional clay bricks. Concrete can be easily molded into a diverse array of shapes—including squares, triangles, and octagons—and pigments can be readily added during production to achieve a wide spectrum of colors. Additionally, concrete bricks boast superior acoustic insulation properties when compared to clay bricks, making them effective for sound dampening.
These advantages position concrete as an excellent choice for aesthetic purposes in construction. However, if the primary goal is a sturdy, long-lasting structural material, clay bricks may present a better option. Concrete tends to shrink over time, whereas clay expands. This fundamental difference in material behavior ultimately results in clay brick walls developing a tighter, more durable seal than walls constructed from concrete bricks. Furthermore, clay bricks generally exhibit superior thermal insulation, which can translate into significant energy cost savings over the long term for building occupants.
Fly Ash Bricks
Fly ash is a fine, powdery byproduct generated from the combustion of coal, and its uncontrolled release can have detrimental health and environmental impacts. Consequently, there are ongoing global efforts to prevent fly ash from entering the environment, which include careful disposal methods and beneficial reuse in various products, notably bricks.
Fly ash bricks primarily consist of fly ash and cement. They are notably lighter than both concrete and clay bricks and, owing to their low absorption rates, demonstrate good resistance to both heat and water. However, high concentrations of fly ash within the brick mixture can sometimes lead to extended setting times and slower strength development during the brick construction process, potentially impacting project timelines.
It’s important to note that these brick types are not rigid categories. They represent common materials used in brick manufacturing, and researchers continuously experiment with modifying the proportions of clay, sand, lime, fly ash, cement, and other additives in a given brick to identify combinations with optimal properties for diverse applications.
Building Bricks for Extreme Weather
As temperature extremes increasingly become the new norm globally, building materials must evolve to effectively handle more severe and frequent freeze–thaw cycles. The question arises: Are bricks robust enough for this mounting challenge?
Recent research conducted by Teresa Stryszewska and Stanisław Kańka, civil engineering professors at Cracow University of Technology in Poland, investigated how bricks within masonry structures of significant historical value have performed under cyclic freezing and thawing conditions over the past 70 years.
Their findings indicate that both the frost resistance and the susceptibility to frost damage in bricks are influenced by several interacting factors, including their mineral composition, the structure of their porosity, and their mechanical strength. Among these factors, porosity structure emerged as the dominant influence.
The researchers elaborated in their paper: “It has been demonstrated that bricks with a relatively high share of pores with diameters smaller than 1 µm in the total population of pores undergo frost damage; i.e., they are characterised by a lack of frost resistance.” They further explained, “Under the influence of cyclical freezing and thawing in actual conditions, these bricks undergo damage but the form of the damage, i.e., cracking, flaking or powdering, depends above all on the structure of porosity, i.e., the fraction of pores of specific diameters.” This implies that bricks with a higher proportion of very small pores (less than 1 µm) are more vulnerable to frost damage. The specific way this damage manifests—whether as cracking, flaking, or powdering—is primarily determined by the overall distribution and size of pores within the brick’s structure.
The primary objective of Stryszewska and Kańka’s study was to develop methods for predicting the long-term durability of brick materials, particularly with the aim of preserving, rather than replacing, original materials in historically significant sites. However, the insights gained into the profound effect of porosity structure on a brick’s ability to withstand freeze–thaw cycles are equally invaluable for engineering new bricks that can better perform in our increasingly severe and unpredictable weather patterns.
What Brick Would You Choose?
When James Orchard Halliwell published “The Nursery Rhymes of England” collection in 1886, it was likely taken for granted that the third pig would construct a house of bright red bricks. At that historical juncture, London architects were indeed favoring bright red bricks, partly to enhance building visibility amidst the city’s often heavy fog. However, in contemporary times, given the expanded definition and material diversity of bricks, sand lime, concrete, or even fly ash bricks would be highly plausible choices for the third pig.
As a previous “CTT” article playfully demonstrated, sometimes fiction offers an engaging pathway to teach complex materials science concepts. So, if you were the third little pig, which type of brick would you conscientiously choose for your structurally sound house? And, crucially, make sure to consider the impact of porosity structure while making your informed decision!