Bricks are an ancient and traditional building material, used both for strength and appearance. Bricks are made from clay, moulded into shape (traditionally 2-by-4-by-8 inches) and fired or baked in a kiln. The colour, hardness, durability and structure of bricks vary with the type of clay used, as well as with added materials such as silica, with the length of time fired and with the temperature of the firing. Bricks are broadly classified as either common, facing or "face," or according to their intended use, such as firebricks.
Common Bricks Use Common Clay
Common bricks are made with basic brick clay, with no attempt at colour control or special surface treatment. They may vary in colour and texture within a single brick. Most are red, the colour coming from iron content in the clay. Common bricks actually are 3-5/8 inches by 2-1/4 inches by 7-5/8 inches, to allow for mortar joints to fill a 2-by-4-by-8-inch space; but these dimensions will actually vary slightly, depending on the manufacturer. Dimensions may even vary within groups of the same common brick. Sides are even but not completely smooth.
Face Brick Is Finished Better
Face brick is more attractive, with sides more accurately finished and smoothed. Colours also are more uniform, both within individual bricks and within brick lots in a shipment. Face brick can follow common brick sizing but also is produced in other dimensions for decorative purposes. Two of the more common variations are king and queen, king being 3 inches by 2-5/8 inches by 9-5/8 inches and queen being 3-1/8 inches by 2-3/4 inches by 9-5/8 inches.
Face Brick Comes in More Options
There are more colour and texture options in face brick than in common brick. Some face bricks have one rough or "struck" face to be placed on the outside or "facing" surface; others have a ceramic glaze on one surface. Colours can vary from white or cream to yellow to red or brown or even almost black. Many face bricks are pressed bricks, made with a technique that compresses the clay and forms very smooth faces, sharp edges and perfectly square corners.
All Bricks Are Graded
All bricks, common or face, are graded for durability. Grade SW is Severe Weather, capable of withstanding freezing temperatures and harsh climates. MW is Medium, able to withstand freezing in less moist conditions. NW is not graded for most use outside but is intended for use in interior walls or applications in which it will be covered by face brick or other surfacing.
The Association for Testing and Materials (ASTM) produces specifications for all types of brick, including one specifically for facing brick. These deal with such variables as resistance to weather or abrasion, minor variations in size, chipping, cracking and warping. FBS is a specification that covers common bricks and some face bricks for general use in walls with some size and colour variations allowed. FBX is a standard for face bricks with a high degree of mechanical perfection and little variation in colour and size.