Red bricks are traditional building materials made from clay, shale, or coal gangue. These raw materials are crushed, mixed, and kneaded before being shaped by hand or machine. After drying, they are fired in an oxidizing atmosphere at around 900°C to produce the final product. Also known as clay bricks, red bricks typically have a technical rating between 75 and 100. The standard size for ordinary sintered bricks is 240x115x53 mm. Their characteristic color is red, though some may appear dark black. These bricks offer good strength, durability, and natural thermal and sound insulation properties due to their porous structure. As a result, they are widely used in walls, columns, arches, chimneys, floors, and foundations. Many historical buildings still use red bricks today, and their origins can be traced back to ancient Rome, where they were commonly seen in classical European architecture.
In ancient China, brick-making techniques were already well-developed during the Warring States period. However, due to strict hierarchical regulations, red bricks were not allowed for common use. Special processes were required to make them suitable for construction. During the late Qing Dynasty and the Republic of China era, the production of red bricks became more accessible to the general public, marking a significant shift in building practices.
The traditional Chinese method of making red bricks involves sealing the kiln during the final firing stage, which limits oxygen supply. This causes the iron in the bricks to reduce from ferric (red) to ferrous (green), resulting in a different type of brick known as blue bricks. Studies show that blue bricks perform better in oxidation, hydration, and weathering compared to red bricks. Ancient Chinese "Qin bricks and Han tiles" have survived for thousands of years, but the complex process, high energy consumption, and low efficiency of blue brick production have led to its decline. With the development of modern industrial technologies like wheel kilns and extrusion machines, red bricks have advanced significantly in production and quality, while blue bricks are now mostly reserved for historical restoration projects.
As technology progresses and environmental awareness increases, new types of unfired bricks are emerging. However, many experts still consider red bricks the best option for wall construction due to their superior performance and comfort. Despite modern alternatives, red bricks are expected to remain a key material in construction for the foreseeable future.
Since the reform and opening up, China's red brick industry has expanded rapidly. However, many small-scale brick factories engaged in indiscriminate land use and farmland destruction led to serious environmental issues. In response, the government introduced policies starting in 1993 to restrict and ban the production of clay solid bricks. These measures included the "forbidden viscosity limit" policy, which limited the production of clay hollow bricks and encouraged the use of alternative materials like shale and coal gangue. These efforts aim to balance construction needs with environmental protection.
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