Before you can start your build you first have to lay a suitable foundation. There are several types of foundation and to make sure that you have the correct one please view our Foundations Project and follow the guidelines.
You may also find our Cavity Walls Project useful.
The actual construction of a cavity wall can vary but in all cases (Building Regulations Approved Document A) the leaves of a cavity wall must be a minimum of 90mm thick with a minimum 50mm cavity in between.
The two skins of a cavity wall are held together by wall ties built into the mortar bed of the bricks and blocks. If the cavity is between 50 and 75mm wide the ties should be placed at a maximum spacing of 900mm horizontally and 450mm vertically. If the cavity is between 76 and 100mm wide the ties should be positioned at maximum intervals of 750mm horizontally and 450mm vertically. The ties should always slope towards the outer skin very slightly to stop any moisture in the cavity being able to travel towards the inner wall.
The wall ties are often used to hold sheets on cavity insulation in place and the type and thickness of this insulation will be dictated by the Building Control officer.
The cavity, in a cavity wall, is there to prevent moisture from traveling from the outside skin to the inside skin. The cavity also, in almost all cases, is used to insulate the internal wall against heat loss from inside.
It is important when building cavity walls to keep the cavity free from debris at all times. Even a dropped trowel of mortar can collect on a wall tie and transfer moisture and cold temperatures across the cavity. We have had many questions over the years about damp and cold spots on walls in an otherwise warm room. This is usually the result of a transfer of cold temperature from the outside wall to the inside via what is known as a bridged cavity. This can be particularly noticeable at the sides of window and doors (reveals) where the cavity is closed to allow the fixing of the frame.
The left hand diagram above shows what can happen when two very common things occur during the construction of a cavity wall. First a lump of mortar has fallen from the trowel into the cavity. This has obviously gone unnoticed and when the insulation has been added to the cavity it cannot get down to the required DPC level. The mortar has bridged the cavity allowing moisture and cold temperatures to pass between the skins of the cavity wall. At the same time, while the garden was being dug, a heap of spoil was left against the wall. The top of the heap was above the height of the DPC.
As a consequence of these two very regular occurrences, ground water can rise up into the soil heap which is probably already damp anyway. This moisture can soak into the brickwork above the DPC and, via the mortar in the cavity, soak into the internal wall. This makes a section of the internal wall cold and even damp allowing the warm air in the room to condense in this “cold spot”. Because the wall is covered by very porous plaster this damp cold spot can be home to any number of mould spores which will soon show as a dark moldy patch which, no matter how hard you scrub, will not go away.
The right hand diagram shows, looking from above, how a cavity wall is returned to close the cavity when meeting a door or window opening. It is at this point that there is least insulation and cold temperatures can travel through the walls. A vertical DPC inserted between the two walls will stop any damp from getting in, but the cold spot inside can still lead to condensation forming on the wall.
Types of Brick
Most bricks are made from clay. This type of clay is imaginatively titled, Brick Clay. Clay bricks (and tiles) are very durable and extremely versatile. In days gone by when bricks were shaped and fired by hand in small batches, different coloured clays, of different compositions, from different areas were used brickwork was as much of a visual delight as it was practical. With the increasing demand for housing larger and larger automated factories are producing more and more standard bricks and the effect is, for the most part, purely practical construction.
Special bricks are still available and experimentation with different clays is advancing brick technology to keep up with the demands for increased durability standards from the EU.
Architects and Planners these days are insisting on re-developing the traditional style of house (and other) buildings using techniques and appearances which
are sympathetic to existing local styles. This may mean that the demand for clay bricks will rise again as, in the 30 years between 1974 and 2004 it dropped from 5,000 million to 2,750 million, just over half. This huge drop in the production of clay bricks is accounted for by the huge rise in concrete products used today together with a massive increase in timber and plasterboard internal wall construction.
The term “common brick” comes from the fact that, although they are fired hard enough to use for most brickwork load-bearing operations they are of a lower quality than facing, or engineering bricks. No attempt is made to control their colour and their composition is such that they should not be used below ground.
They are used mostly for indoor partitions and for parts (or skins) of walls that will not be seen. They are lighter in weight than facing and engineering bricks. Their use is, as described above, being overtaken somewhat by the use of concrete and lightweight blocks for internal partitions.
An engineering brick goes through a more elaborate process of clay selection, careful crushing, firing and moulding to make it a very hard brick indeed. The process delivers a brick which is has very high compressive strength with very low water absorption. Engineering bricks can be used underground and are often laid as a damp proof course. They are rated in two classes, A and B with A being the strongest and least absorbent. This type of brick is used in situations requiring the strongest of work.
There is a number of different types of facing brick but generally they are the “face” of the building. They are hard burned to give them strength and durability which they need to withstand the hugely varying temperatures and climate available in the UK, not to mention the acid attack from smoke and soot from any number of furnaces and cars.
Stock Facings, or stocks, are a soft, irregular facing brick produced by pressing wet clay into sanded moulds. It is by using sand to release the stocks from the mould that gives them their soft texture and slightly irregular shape.
Most facing bricks in the UK are shaped by wire-cutting. The tightly packed clay is pushed through a die where it gets its perfectly rectangular shape. The face is then added. The block or column of faced clay is then wire cut into individual bricks and fired in a kiln.
Waterstruck bricks are released from the mould by water. They contain no holes or frogs and have smoother edges.
As you would imagine, these bricks are hand-made. An extremely expensive process which, as the clay is folded into the moulds, produces distinctive creases (smiles) in the brick. Handmade bricks are used in the most prestigious of buildings.
Another brick that does exactly what it says on the tin. Reclaimed bricks can be a variety and mixture of the above facings. The fact that they have been used once and reclaimed gives them creases and marks which will add something to any building they are used on. Because reclaimed bricks tend to come from older buildings they are often in imperial, rather than metric sizes. This makes it difficult to integrate them into larger, modern walls, so special reclaimed “panels” are often inserted.
Special bricks are so called because they are made to fulfil a specific task. An example of a special is a bull nosed brick shown in the diagram. This type of brick is used to finish off the top of a wall or even as a window cill. Other often used specials include plinth bricks, copings, arch keystones and many others. Brick companies can make a brick into almost any shape you like as long as you are prepared to pay for it.
All bricks have different uses but all need to withstand a certain amount of wear and tear. Bricks are crush tested to determine their usability and the crush testing result for each brick type is an average figure based on the crushing of twelve bricks of that type. Crushing strength is measured in Newtons per mm square and the softer of facing bricks will have a crushing strength of about 3 – 4 N per mm square whereas engineering bricks will not fail until approximately 145 N per mm square.
As different bricks are used for different conditions, and in different walls, so different ways of laying them are employed in different situations. Some walls are laid so you can only see the ends of the bricks, some in a way which only leaves the sides visible. These different ways of laying bricks are called “Bonds” and the most popular are listed below.
Brickwork and blockwork bonds
Bonding, or tying together individual bricks and blocks can be done in a number of ways. However it is done it is imperative that the maximum strength possible for the task of the wall is obtained. Some popular bonds are shown below together with an explanation of where they are most likely to be used. Brickwork or blockwork bonding should be laid out dry before you start to make sure the bond works. Sometimes bricks should overlap the brick below it by half of its length (half bond). Some brickwork types use a quarter bond where one brick overlaps another by a quarter of the width of a full brick. Believe it or not buying a pack of dominoes for three pounds, and practicing brickwork bonds with them can save you a great deal of time and money when it comes to building a retaining wall in the garden.
The long face that you can see in a brick wall is called the Stretcher face. The shorter “ends” are called Headers. Stretcher bond is the most commonly used in house construction because of the economy of bricks it allows and the speed in which this bond can be laid in most constructions which only require a single (half brick) skin.
Two stretcher walls can be built back to back and tied together using wall ties to form a double (single brick) skin. This type of tie is called a collar tie. This is a way of getting an attractive face on both sides of the wall but not the strongest method of producing a single brick wall as the ties between the skins are a weak point.
Stretcher bond uses 60 bricks to the square metre in a half-brick, or single skin wall. This is obviously doubled to construct a double skin, or One-brick wall.
You can see clearly in the diagrams how each brick in the stretcher bond overlaps the one below it by half of its length. Turning corners with stretcher bond is simply a matter of placing one brick at right angles to another. This automatically continues the half bond. To finish off the ends of the wall a brick is broken in half (half batt) and laid to keep the end of the wall in line vertically.
Stretcher bond is not the strongest of bonds however and if a wall of any length is built, piers must be inserted to maintain strength.
There are two ways to end a stretcher wall with piers. The first, above, shows the use of a half-batt in alternate courses while the diagram, left shows the use of a three-quarter batt.
In some brickwork bonds a gap develops which is not the same size as a full or half brick. In these cases a brick is cut to fit the gap and this cut brick is called a closer. Some bonds do not work at all without closer's and the same size/type of closer is used in every (or every other) course. Where the closer has common usage it is often named, and “King” or “Queen” closer's are often seen as are half and three-quarter batts.
Most bricks used for home construction in the UK have indents in the top of the brick. This indent is called a frog and if bricks are laid to British Standards, as they should be, the frog should be laid upwards and filled with mortar. British Standard Code of Practice BS 5628-3 states. “Unless otherwise advised, lay single frog bricks with frog uppermost and double frogged with deeper frog uppermost. Fill all frogs with mortar...." This maximises strength, stability and general performance of the brickwork.
When the frog is laid upwards, the load is evenly spread throughout the width of the brick all the way down to the foundations. If the frog is laid down, the load is forced to the outsides of the brick. The recommended maximum number of brickwork courses to lay in a day is 16.
Other bonds used in home or garden construction are:
English bond (also known as Ancient Bond) requires quarter bond work in its construction of a course of stretcher bricks and a course of header bricks laid alternately. It is the strongest brickwork bond. It is however, one of the most expensive because of the labour time. The Victorians, when building many of their classical gardens, introduced a variation on
English Bond, called English Garden Wall Bond which introduces the course of headers in between five courses of stretchers. This maintains the strength, looks attractive and is cheaper and quicker to build.
It can be seen from the diagram that English bond requires closures on each course to maintain the bond. This type of closure, a brick cut down the middle of its length, is called a Queen Closer.
Not quite as strong as English Bond but used for is visual affects, Flemish Bond is laid using stretchers and headers alternately in each course to give it a quarter bond finish. Flemish Bond also has a “garden wall” variant in so much as the number of stretchers in between the headers can be increased.
As stated before the most common bond used today is Stretcher Bond and for DIY purposes this is a perfectly adequate bond especially for use in the garden. The problem with single skin Stretcher Bond is that it has very little strength when pushed from back or front. Despite this is it often used as a retaining wall and more often that not will buckle and fall over under the pressure of soil. Our brickwork project is about building a garden wall and shows you how to lay bricks.
Last year Diydoctor received 4,820 questions regarding building retaining walls. Over 50% of those questions were sent because the retaining wall which was already in the garden had ceased to retain!
>Quetta Bond is a brickwork bond designed specifically for the Industrial use of retaining and load-bearing support. This bond can be easily adapted for garden use where a very strong, attractive retaining wall is needed.
The wall is built as shown using stretchers and headers and the voids created by this bond are filled with concrete. The first course of this type of wall is built laying the bricks onto the concrete foundation before is has set. Steel reinforcing rods are driven into the concrete foundation, through the voids and further courses built up around these rods. When the voids are filled you are left with a very attractive, very strong garden wall which will retain pretty much anything you throw at it!
The steel reinforcing bars (12mm High Tensile bars are recommended) can be bought at any builders merchants and easily cut with a hack saw.
For extra strength with any type of wall, a galvanised steel mesh can be laid into the mortar course. A little like chicken wire this mesh is called Expanded Metal Lathing and is available from Builders Merchants in sheets and in rolls. For the DIY enthusiast it is far more useful in rolls which come in various widths ranging from 50mm to 450mm. The mesh can be cut with a hacksaw or tin snips and can virtually double the strength of some walls.
This bond is used for decoration in garden walls as shown but serves the useful purposes of allowing some visibility and also creates less resistance to strong winds.
To finish the top of a wall a course of bricks is often laid on one of their stretcher edges. This is called, again inventively, a Brick On Edge course. Another way of finishing a garden wall is by using coping stones. Coping stones are cast with an angled top to allow the water to run off and, as with window cills, usually overhang the brickwork slightly so the water does not run down the face of the brickwork and stain it. Coping stones can be seen in our Laying Bricks project
Concrete and lightweight blocks are widely used in all areas of building and DIY. They can be bought with a “Fair face” for work which is seen. They are much quicker to lay given that 1 standard block is equivalent to 6 bricks (For buying purposes there are 10 blocks to the square meter when the block is 440mm x 215mm) These dimensions are the same as two bricks and 1 mortar joint wide, by 3 bricks and three mortar joints high. This allows blocks and bricks to be used (and bonded) together in a simple way as can be seen in the stepped foundation diagram in the first chapter.
Blocks come in various thicknesses and the extension we are building will be built using a lightweight block of 100mm thick. Blocks can be laid flat and walls built using flat blockwork Stretcher Bond are incredibly strong. Special blocks are used for various applications and one of the most common of these is the “Hollow” block. The hollow block can be laid as it is and the voids used as an insulation quality, or the voids can be filled with concrete to make a very strong wall.
Concrete blocks are almost always used in foundation walls as they are so much cheaper in terms of labour time to lay.
A word of warning to the DIY bricklayer here. Concrete, or any other blocks, are not easier to lay than bricks. Getting a block level, on a flat level mortar bed is every bit as difficult, if not more so, than laying a brick. Bricks can be picked up and lightly pushed into a bed of mortar with ease. A block however may take some “persuading” with a hammer or the handle of the trowel (not recommended). Because of its surface area, hitting a block in one place will make it move in another and then the block will start to rock.
Because of their weight, hitting a block will cause the one underneath to move also and laying a block wall, even though the blocks are heavy and cumbersome, requires a light touch. We would not recommend laying more than 5 courses of blocks in one go.
Lightweight blocks can be used in conjunction with all types of building. The blocks have all of the qualities needed to satisfy the Building Regulations both inside and outside, load bearing and non load bearing.
The strength of lightweight blocks in very deceptive and their compressive strength, needed to form the load bearing inner skin of a cavity wall, is far more than is required. The lightweight nature of the blocks allows them to be picked up and laid with one hand, a huge bonus when you are laying blocks and your back will thank you for using them at the end of a long day.
Thermal resistance ( U ) values are met much more easily with lightweight blocks and their ability to deaden sound makes them perfect for modern domestic internal use. The thermal resistance qualities alone can save a great deal of money on other insulation.
Cutting lightweight blocks could not be easier. They can be cut to any shape or size using an ordinary carpenters saw. Do yourself a favour though and don’t actually borrow the carpenters saw to do it….Buy a cheap saw at the DIY store ! Lightweight blocks can be drilled as easily as wood and the only real problem is getting a strong fix to them for shelves, cupboards etc. However special light=weight fixing plugs can be bought from Builders Merchants which are literally screwed into the blocks and then normal screws fixed inside those.
Lightweight blocks are considered t be non combustible giving them a great rating in the fire resistance section of the Building Regulations. Their ability to withstand sulphate attack allows them suitability in the ground and their resistance to frost has been proven time and time again. Freeze-Thaw action has already been mentioned in the preceding chapters and lightweight block have shown no tendency to lose compressive strength under the conditions associated with freeze-thaw.
Lightweight blocks have millions of tiny air pockets in their structure but these ar not connected making them able to withstand damp conditions well.
Glass blocks are now widely used. These can be laid as normal blocks, i.e. with sand and cement joints, or by using special frames and spacers which usually come in kit form with the blocks. If laying glass blocks with sand and cement it is as well to remember that glass has no porosity at all and if care is not taken a wet mortar mix will very soon squeeze out all over the face of the blocks. Glass blocks can be laid indoors or out and are an excellent way of letting light into a space while still keeping that space separate from others. They come in a variety of sizes with a clear or frosted finish for maximum privacy. Glass blocks are tested to see how long it takes before fire makes them unstable and they are also tested for their thermal insulation qualities. This, if the correct block is chosen, will keep them within Building Regulation guidelines.
Scaffolding, in the tube and fittings form, should not be attempted by any DIY'er. There are many reasons why a normal tube scaffold should not be put up in a DIY way. Scaffolding is not only a trade in itself but it is a very dangerous one and if a
scaffold is not put up 100% correctly, the results can be fatal. In 2003/4, falls from height accounted for 67 fatal accidents and nearly 4000 major injuries...and yes....it could be you.
Tower scaffolds can be bought, or hired, to complete jobs at home safely. Scaffold towers are easily portable and can be carried, in lightweight sections, directly to their place of use. Most have lockable wheels so once a job like cleaning out gutters is started, the scaffold can simply be pushed further down the line allowing safe access to all parts of the project.
The tower, above, is called a micro podium, is designed for work at between 1.2 and 4m and is absolutely idea for most work around the home. Platforms sit at height from 1.2. to 1.6m bringing most first floor operations within easy reach. These towers, or podiums, can be erected by a single person but to erect higher towers two people should work together.
Scaffold towers of all kinds can be purchased but it is more usual, in a domestic/DIY situation to hire them.
In 2005 regulations have been bought in to cover working at height. A copy of these Health and Safety regulations can be seen at this web address www.hse.gov.uk/pubns/cis10.pdf
The bond that you choose to build your wall with is up to you but it’s a good idea to practice your brickwork before you start a major project.
Many of the frequently used brickwork bonds can be seen in the chapter on brickwork and blockwork so this project is simply about the technique of actually laying bricks. The same technique is employed whatever you are laying and there are a few important things to remember.
If the last brick you laid is not level, do not bash it with a trowel, hammer or anything else. It may be that while you have bashed that particular brick into position, you have knocked several others out. However “robust” a brick wall appears, while it’s wet it can move all over the place if not handled properly. This is especially true of heavy blocks.
If your bed of mortar is the correct depth and the mix is pliable enough you should be able to place the bricks down gently and with a gentle twisting motion, get them into the correct, level position. Now and again a gentle tap is required with the handle of a trowel but after this tap a bricklayer will always stand back to make sure nothing else has moved. If time and care are taken over the first few courses the rest of it gets easier. If the first few courses are not level in any way, it becomes a really hard job to get a nice finish.
To make sure your wall finishes at the right height, get a timber batten the same length as the proposed height of the wall. Using the measurements outlined in the Brickwork chapter, mark the proposed courses onto the batten working from the bottom up. See where the last mark comes to on the batten and measure from there, to the end of the batten. Whatever is left over can be “made up” by increasing the depth of the mortar in each bed joint slightly (a bed joint should be no more than 15mm) or if it is easier to add another full course, the bed joints can be made a little thinner. We would not recommend laying a joint of less than 6mm .
As you build the wall check not only the line, level and how upright the wall is. Check the level across the width of the wall. Bricks and blocks can show level along their length. Can show, by looking at the spirit level, to be perfectly upright both from the front and from the side. Then you stand back and take a look and the job is dreadful. This is always because the wall is not level across its width. The bricks tilt one way and then the other but at least one part of the brick is touching the spirit level so the wall appears to be correct. After a few years you get the hang of “feeling them down” but until then the spirit level, in all directions, is the best friend you have. It may look a little exaggerated in the diagram but, if you want to try it yourself, you will see it is not!
In the sequence of images showing the laying technique, you will see a small “boat” level across the wall. This is carried just to make sure of a perfect level across the wall.
To begin laying, place some of your mix on a “spotboard” close to the wall. Use your trowel to roll the mortar down the heap until it forms a sausage at the bottom. Slide the trowel under the sausage and then let it slide off again into position for the first course of bricks.
Use the point of your trowel to form a V in the mortar bed. If you have seen our project on laying ceramic tiles you will know that this V allows for displacement of mortar as you push the brick down. Once again the same principle is applied to many jobs.
Place your bricks carefully, but firmly onto the bed. Push down with a slight twisting movement leaving a bed of 10mm under the brick. Place the spirit level at the back (or front) of the bricks to check they are being laid in a straight line. Make sure you fill the joints between the bricks.
These bricks are being laid to stretcher bond and once two or three courses are built its time to check for plumb on the end. Do this on every course.
The wall needs to be checked every course for plumb at the front, at both ends, on every course. You can see the boat level in the picture also. If the wall starts right, it should end right!
The first course is laid throughout the length of the wall with the ends built up to about 5 courses. These ends then become known as corners. When the corners are up they are used as a template for the rest of the wall by stretching a string line (Bricklayers lines, and line pins) can be bought from all DIY store. The pins are pushed into the mortar joints and the string stretched between them. The bricks are then laid so the top edge of each brick is touching the line. If your corners have been built properly, the rest is easy. Do not use a line for a wall that is over 6m long as it will sag in the middle. For walls this long you need to build another “corner” in the centre of the wall..