Brick Types and Properties: Everything You Need to Know

Bricks are one of the most widely used building materials. Although many people may not be aware of this, there are various uses for brick types and properties across the construction industry. The vital difference between bricks and blocks is in size, composition, weight and shape. Blocks are typically made from concrete and are larger in comparison.

However, building bricks offers far more aesthetic advantages. Brick sizes and brick dimensions can still vary drastically, but they all are capable of withstanding immense loads. There are more brick types which help the insulation of a building, longevity, and bricks generally are a more cost-effective solution.

Brick properties

Brick types and properties vary and manufacturing processes affect how bricks perform, as well as how they appear. Their aesthetic appearance and physical properties are also impacted by the type of clay used. The most important properties of bricks may be regularly detailed as physical, mechanical, thermal and durability. However, when going into detail, the vital properties of bricks may be described as:

Strength

This is arguably the most crucial property of brick, particularly if they are being used for load-bearing walls. Clay bricks should have a minimum compressive strength of 9N/mm² for a building up to two storeys high, and 13N/mm² for anything higher.

Bear in mind that if the crushing strength of a brick is below 3.5N/mm², it should not be used. To test this, you can drop a brick from a height of approximately one metre and it should not break. However, the compressive strength is down to the temperature of the brick being burned and its composition of clay.

Colour

The most common brick colour is red. Good quality red bricks have a uniform colour throughout. However, modern manufacturing methods have allowed for bricks of almost any colour to be produced. There are three factors to consider: the first is the clay used and the colour running through the middle when the brick is broken.

The second is the mineral pigments, engobes and sand used for the brick, and the third is the atmosphere of the kiln. A kiln fired at a too-low temperature will produce poor-quality bricks, but overfiring can cause bricks to shrink. Oxidising, which uses a high level of oxygen during the firing process, is primarily used for creating red bricks.

The clay minerals such as iron oxide give the brick colour as it absorbs oxygen. Whereas manganese oxide allows bricks to turn a brown colour. A low level of oxygen during the firing process can cause discolouration - metal oxides are used to compensate for the lack of oxygen. For red bricks, this can result in a light brown effect and, with yellow bricks, you could be left with shades of grey or green.

Durability

Adequately manufactured bricks are incredibly durable, often lasting hundreds of years. Due to some brick types and properties, some have more durability than others. This depends on when and where a brick is laid. Brickwork laid in the winter months could prove challenging as it needs good protection from the elements.

Engineering bricks protect from constant frosty or damp conditions and are produced with core holes to allow extra support from steel bars. This makes engineering bricks a good choice for foundations and infrastructures such as tunnels. Because of differing weather conditions, it is important to use the correct type of brick for your project.

There are three ratings you should look out for:

• F0: No frost resistance - not to be used in external settings (if there is not a durability rating on a brick, you should presume it is F0).
• F1: Moderate frost resistance - not suitable for excessive freezing conditions and thawing. Can be used for brickwork between eaves and a dynamic cone penetrometer (DCP), but cannot be used below a DCP or landscaping.
• F2: Frost resistant - suitable for all conditions.

Absorption

Brick absorption value varies from product to product. Absorption refers to the quantity of water a brick can absorb, as a percentage of its total weight. Ordinary building bricks should not have an absorption greater than 25% and the preferred absorption rate is between 12% and 20%. For engineering bricks, closer to 12% will give a much better result.

However, if water absorption is below 12%, this can result in difficulty in forming a bond between bricks and mortar. On the other hand, bricks with a high level of water absorption can absorb moisture from the bedding mortar. Water could, in some cases, move slowly towards the inside wall regardless of its thickness.

For areas with heavy rainfall, constructing a cavity walling system by creating a gap between two parallel layers of bricks to avoid water moving inside could be a viable option. To test the water absorption of a brick, you first weigh the brick when it is dry, then leave it in water for 24 hours. The brick is weighed again and the difference between the two is the water absorption percentage.

Size

This is something you probably would not have thought about before, but brick sizes vary across the world, with the UK standard brick size being 215mm x 102.5mm x 65mm. But a 10mm allowance is applied to make way for mortar joints, so it is 225mm x 112.5mm x 75mm.

For context, the Australian standard brick size is 230mm long x 110mm wide x 76mm, and in the US, the standard brick size is 8 in x 3 5/8 in x 2 1/4 in. A standard brick size makes it easier to plan construction projects and determine how many you will need.

As a template, a wall of one square metre will require 60 bricks. If bricks are too small, this means more modular is needed which increases the cost of a project. But bricks that are too big slow down a project if they become difficult to transport.

Form and shape

Regardless of brick types and properties, they should ideally be rectangular, with well-defined, sharp edges and an even surface. However, some brick manufacturers can produce specially designed products. These include:

1. Perforated bricks: Iron bars are pushed through the brick during moulding to create holes, which help the brick to burn and dry quicker. The perforation area should be under 45% of the brick face.
2. Cavity or hollow bricks: These are approximately one-third of the weight of a typical brick and are quicker to work with (hollow and cavity bricks can be laid four times faster).
3. Plinth, splay or cant bricks: made with a missing edge, these are used for door and window jambs.
4. Coping bricks: They come in different sizes and shapes and are primarily used for parapets to help drain rainwater.
5. Bullnose bricks: With a minimum of one rounded corner, bullnose bricks are used for openings to windows and doorways to soften the corners. They can also be used to build steps and window sills.
6. Gutter bricks: These are produced with a central semicircular cavity running throughout the brick length to be used in drains.

Brick types

Different manufacturing techniques can create different brick types and properties as well as aesthetic effects. There are three general brick types: engineering bricks, facing bricks and common bricks.

• Engineering bricks – These bricks have low water absorption and high compressive strength. Engineering bricks are chosen primarily for their physical attributes, as opposed to their appearance. They can come as either Class A engineering bricks (125N/mm² with <4.5% water absorption) or Class B engineering bricks (75N/mm² with <7% water absorption).
  
• Facing bricks – The most common type of building bricks. They are used predominantly in external walls, meaning their aesthetic qualities are almost as important as their resistance to water, fire and damage. Facing bricks can be classified as either soft mud (stock) or extruded (wire-cut) bricks.
  
• Common bricks – Created using basic brick clay, common bricks are used for a wide range of structural and internal areas including multi-residential walls and vertical brick walls. Unlike facing bricks, common bricks have a rugged texture. Common bricks are also primarily red, whereas facing bricks can come in various shades and are pressed for an even and smooth shape. But like facing bricks, common bricks are water and fire-resistant. 

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