As part of the RICS competency on construction technology, we’re going to cover bricks today. A lot of technical and illustration is needed to explain the different bonds and bricks. I hope this is going to be helpful to you.
Bricks in general
The size of bricks and blocks can make a big difference to the construction process because they are important materials. There are many types of bricks and blocks that could be used in construction, but there’s one size that affects how everything else will be built. We’ll talk more about this as we go on, so let’s get started.
Bricks and blocks are ‘man-made’ concrete building materials that you can use to build anything you want. They are made of a variety of materials, such as terra cotta, travertine or clay bricks.
Stone is quarried and shaped, but it also often occurs naturally. Additionally, it was often used as it was found below cliffs or outcrops or on beaches, or from the general stones on or in the ground.
Artificial stone and reconstructed stone are not natural. Artificial stone is made by mixing stone with cement, water, and any other coloring materials. Reconstructed stone uses the same mix but omits the coloring agents because they use only natural stones at the end of the process.
For projects where the original stone is no longer available and the quarry has been depleted, it’s sometimes cheaper to use reclaimed stone.
Most of the structures we will consider are made from bricks and blocks. There is, however, a need for explanation, so we will start by looking at materials, sizes, shapes, etc.
- Some materials can be used to create bricks and blocks, such as calcium silicate and concrete.
- You can get bricks and blocks in different sizes, shapes, and materials.
Topics on bricks other than the standard rectilinear shape are found in British Standard 4729.
Brick surfaces have names:
- The top surface doubles as a bed.
- The bottom surface also doubles as a bed.
- Ends are headers or header faces
- A side is another name for a stretcher or stretcher-faced panel.
Mortar is a type of material used to bind bricks and blocks together. Mortars are not made out of cement, which is generally a dry powder. Cement may or may not be present when making mortar, depending on the type of wall. The topic on mortar will be discussed in more detail later in this blog post.
Bricks are made in different sizes, but in this text we’ll only focus on the standard metric brick. A standard metric brick has measurements of 225 × 112.5 × 75 mm and working measurements of 215 × 102.5 × 65.
Brick manufacture is complicated, because the final size of a brick can be slightly different from what you expect. This is due to things like shrinkage or distortion when drying or firing bricks. That’s why there are two sizes for brick – coordinating and working. Coordinating dimensions are the size of a brick plus the mortar required on one bed, one header face and one stretcher face. Working dimensions are the size to which manufacturers will try to make bricks.
The nominal size of a brick is the difference between the working and coordinating dimensions. The usual nominal size is 10 mm, with a layer of mortar into which the bricks are pressed when laid. Most often this nominal size is the thickness of six bricks or one inch- American units.
Our content is sized according to importance, rather than just by time.
The term nominal sizing refers to the size given by a manufacturer that allows for slight variation. The variations in size – larger or smaller – are generally given in British Standards. Variations on individual bricks may vary, as they’re allowed an extra few millimeters as they are pressed into the mortar, but they will fall between the dimensions width of 225mm and thickness of 75mm.
Durability of bricks
Durability is an important consideration when building in areas with freezing temperatures or high levels of salt. For a classification of durability, see BS 3921.
The durability of brickwork is dependent on two factors: resistance to frost and soluble salt content. Frost resistance falls into three classes: frost resistant (F), moderately frost resistant (M) or not frost resistant (O). Soluble salt content is classed as either low (L) or normal (N). So, one could have a brick that is frost resistant with normal soluble salts content and this would be classified as FN. Likewise, a brick that had no frost resistance and had low soluble salt content would be classified as OL.
Mortar placed below or on top of bricks is called a bed. Mortar placed vertically in between bricks is called a perpend.
Regularly spaced, matching sizes allow these bricks to be pieced together in a number of different ways. Building brickwork to the specific coordinate size is important for achieving the desired appearance.
Other elements like bits, lints, and window halves are manufactured to fit openings that are calibrated in whole or cut bricks.
When creating a brickwork design, you should make sure that the bricks are all the same size so they will fit properly.
- The height of the lintel is 176 mm, or 3 x 65 mm.
- The width of the window opening must be a multiple of half a brick, plus the perpends. This means that 8 × 102.5 + 9 × 10 = 880 mm or 4′ 10″.
- The length of a lintel has to be the width of the opening plus its pieces that are built into the wall- the rests.
- Wall rests are created by using cut bricks. The number of rests needed varies depending on your load, but in this case they are half the length of a brick each, less the mortar required in the perpends between the lintel ends and adjacent brickwork.
- The lintel length is 880 + 2 x 102.5 = 1085.
Sometimes brick can be just one long, rectangular piece of material. It might also have a deep indent on both sides, called a frog. Frogs can be either shallow or deep but they won’t exceed 20% of the size in total.
A brick might be:
- Cellular – having cavities or depressions exceeding 20% of the volume in total.
- Perforations that do not exceed 20% of the brick’s total volume; at least 30% solid brick across the width.
Bricks can be manufactured to fulfill many different functions, such as adding structural support, resisting moisture absorption, or being used as decoration.
The majority of bricks used are from the ‘All other’ category, but don’t have a problem resisting the weight of most buildings. That being said, it’s important to remember that there are limits for bricks when it comes to absorbing water. If bricks will be used for an external wall and you want them to resist weather, it would be foolish to use extremely absorbent bricks or let the absorption level for engineering bricks fall below those required by DPC. At the same time, if a DPC is not in place and you’re using less than average water-absorbing bricks, this might not be necessary and could actually end up causing problems down the road.
The vast majority of bricks used are in the “All other” category, but this compressive strength is perfectly adequate for all but the most severe loadings. However, the water absorption should be limited if you need your external walls to resist weather conditions. It would be foolish to build a wall that has bricks that can absorb lots of water if these bricks were going to become damaged from weather conditions. On the other hand, if the brick is low on water absorption and you’re required to use drying agents, it might be an unnecessary expense.
Testing of bricks
Brick must be tested to comply with British Standards. The tests typically include dimensions, soluble salt content, efflorescence, compressive strength and water absorption.
Bonding of Bricks to form walls (types of bonds)
One of the first building concepts ever developed–bonding bricks together–is still being used today. This quality of a wall is created with layers and various patterns that change from course to course. You can mold your bonding pattern by changing the cut and whole bricks in these layers, or even by using bricks that are shaped differently than standard rectangles.
Cutting a brick in half can be tricky. It’s easy to draw out the lines correctly, but it’s not so easy to cut along the lines with precision. Fortunately, there is a simple solution that will work for any type of brick – even one that has been damaged or deteriorated. By cutting the brick along its half height, you create the perfect surface against which to rest other bricks. You could call this cut a ‘half batt’.
Building walls with straight vertical ends is possible because of the simple cut at the end of the brick.
Another common pattern is called English bond. It is more complex than stretcher bond and it is used only in situations where the wall has a thickness of 215 mm or one brick. If we look at the illustration on this blog, a drawing of two adjacent courses of this type, we can see how another of the standard cuts can be put to good use when bonding bricks together as well as towards supporting vertical end-walls. For walls thicker than one brick, a further development for bonding comes into play. Every bond in this category displays a grouping of bricks which repeats across each course. In some instances the pattern repeats across every course, in others adjacent courses display the mirror of that pattern. In one-brick walls in English bond the pattern is two bricks side by side and turned through 180 degrees (this type is also known as sectional bond). This pattern will be visible in all of the following figures.
What are the thickness of walls
It’s not common for wall thicknesses to be listed in millimeters, but you can get a general idea by adding the “half brick” amount of 102.5 mm and the mortar thickness of 10 mm to understand what that would mean. So a “half brick” thick wall would be 102.5 mm, a “one brick” thick wall would come in at 215 mm, and a “one and a half brick” thick wall would be 327.5 mm.
This is a particularly helpful piece of information when creating plans, creating sections, and drawing out detail. Many contracts have specifications of materials and workmanship that should be included in the document. This terminology can come in handy if you’re using brickwork to describe the details. Whether it’s a standard form contract or not, having the size of bricks mentioned will add more focus to your document.
Types of bonds
We will demonstrate how bond is determined by illustrating three key points in the construction of any wall:
- A corner or edge of a wall. Called scuntion or scuncheon.
- The point where two straight lines meet, called an intersection.
- The right-angled corner of a wall, known as the quoin.
Before we begin, you should know that this is not a complete list of bonds or situations. When reading other texts, you’ll find variations on the bonds discussed here and many other types of intersections and thicknesses.
Stretcher or common bond
The first and most basic form of bond is illustrated here.
- Only used for walls of half brick thickness, this is the only practical bond that can be used on a wall of this thickness. Though we’ll build ‘mock’ bonds of other kinds later. A little of that later.
- Only show stretchers on the general face, with occasional applications at quoins, scuntions, and intersections.
The thickness of the walls we will consider now vary from 215 millimeters to 327.5 millimeters – 1 to 11/2 bricks thick.
First we will show English bond and continue with Flemish, Scotch, and garden wall bonds. Finally we will show Quetta and Rattrap bonds, both of which are always 327.5mm and 215mm thick respectively. Sectional bonds are shown as hatched lines in all of the following figures.
- Strongest bond
- This bond maximizes the strength of the wall
- It is used on single-brick walls and upwards
- Note how the sectional bond changes as the wall’s thickness increases.
There is a pattern on the face of the wall that slopes in an organized, predictable way. You can tell by looking at it that there must be headers and stretchers mixed together.
- This bond is not so strong as English bond
- It is used on walls made of one brick width.
- Noting how the width of a secant varies in direct proportion to the wall thickness, one can see that
The decorative pattern on the face of walls shows alternate headers and stretchers in each course, with the headers centered under and over the stretchers in adjacent courses.
This drawing is the sectional bond. The hatched portion is a void, not the actual sectional bond. This is an attempt to produce a more weather-resistant form of wall than the one brick, solid wall commonly used in housing at the time without using any more bricks or splitting the wall into two layers joined with wall ties. This idea never took off because, although it does provide a way for moisture from outside to travel onto the inside surface of the wall, it adds another step to production and slows down construction.
Bricks are the most common type of masonry wall we see today. They’re all “layed on edge” (or stacked vertically). Due to this, our walls are 1 and a half bricks thick. When building bond with bricks on edge, there are a few things to keep in mind:
- Bricks should have plain beds – no raised frogs, cavities or perforations.
- If the wall is to be rendered or plastered, choose bricks with shallow frogs or small perforations
- If the wall is covered over in some other way, then the size of a frog etc. doesn’t matter.
- Coverings could include vertical tiles, slates, or board-like structures that are half an inch thick.
- This wall would solve the problem of moisture crossing the wall.
This type of bond uses bricks and concrete. Reinforcing rods are installed in weakened brick bonds to strengthen the walls. For example, for brickwork that is complete and mortar has hardened, concrete is then poured into the gaps between the bricks and rods. This type of construction may not be an economically-feasible solution for keeping out the weather once the cost of overcoating is added, but it is a good option for noninhabitable buildings or garden walls because they don’t require as much upkeep.
Like the Quetta bond, the Rattrap bond are laid on edge, which can result in an interesting face pattern. The following information about Quetta bond applies equally to Rattrap bond, with a very low chance of keeping out weather effects. A stronger bond than Quetta, Rattrap is often used for industrial or agricultural buildings. It can be made more weatherproof by over-cladding, and the bond usually involves one stretcher to one header, as seen in the illustration above
I hope this answers the different types of brick bonds, the sizes and common misconceptions about working with bricks. I sure have learnt the two new bonds of Quetta and rattrap bonds from doing this research.
you can get more details about this from this book: Construction Technology: an illustrated introduction by Eric Fleming.
If there are any mistakes or suggestions, please do not hesitate to leave a comment below.