1. Whether building a wall in the garden, laying a patio, adding an extension, converting a garage into an office or simply making a concrete path, one question is certain to crop up "how much do I need?".
It is one of the most important questions and one that tends to cause the most confusion when trying to work out the answer. If you are planning a garden wall, for example, you will know the length and the height, but how many bricks are necessary? Even more important, how many bags of sand and cement will you require? There is nothing more frustrating than starting a job only to run out of materials part way through!
sizes vary slightly because of the way they are made but for ease of
calculation the size of one brick is taken as 215mm x 102.5mm x 65mm and for
normal brickwork the joint between the bricks bath vertical and horizontal is
deciding how many bricks are required, the thickness of the mortar joint is
included into the calculations, making the measurement of the brick 225mm x
102.5mm x 75mm. By adding the mortar joint thickness any slight variations in
size for the bricks are taken into account.
When determining how many bricks are required you should first work out the area of the brick work as follows:- Length of wall say 4m, height of wall say 0.5m, multiply the two figures together, 4m x 0.5m = 2 square metres. Square metres are often written as ‘m2’ or sq.m’. For an easy rule of thumb guide, you should allow 60 bricks per square metre for the building of a single skin wall. This is known as a half brick wall. The style is known as Stretcher Bond with only the long ‘Stretcher’ faces of the bricks visible.
For example a 2 square metre wall, you will need to multiply 2 (area of brickwork) x 60 (number of bricks per square metre) = 120 bricks. If you intend constructing a one brick thick solid wall, then you should allow for 119 bricks per square metre. So for a one brick thick solid wall you will need 2 (area of brickwork) x 119 number of bricks per square metre) = 238 bricks. The visible ends of bricks are known as 'headers’.
figures do not allow for wastages or breakages, so it would be advisable
to add a few extras to the order to make certain you don't run short. Normally 10%
extra should be sufficient.
The next question to be answered is how much mortar will I need?
To find out how many bags of sand and cement you will need for example if you had a wall 4 meters long and 0.5 meters high, and used 120 bricks, you need to divide the total number of bricks (120) by 40 (coverage of one bag)
120 divided by 40 = 3, So 3 bags are required ( if your mortar mix was 1:3 you should by 1 bag cement and 3 bags sand)
Concrete blocks are much easier to calculate. Each block is 450 x 215 x 100. Ten blocks will construct approximately 1 square meter of wall, with 1 bag of sand/cement mix enough for 10 blocks.
First, to build a brick wall outside, you must build a base (called a footing) for the wall to stand on. Footings must be dug well into the ground (normally about 700mm down). The footings need to be placed at least at this depth as the ground temperature remains constant at this depth. If you are building an extension to your house, it is important to ensure your footings are deep enough prior to constructing anything!
Once you have dug your footings, pour concrete into the trench, (at least 600mm* wide and 250mm* inches deep for cavity walls) to provide a solid base to build your wall onto.
* these footings may need to be larger - depending on how high the wall is to become (the example should be enough for a one story high wall).
The footings can either be filled with ready mix concrete from your local concrete mixing company, or you can mix it yourself. To mix it yourself, mix 6 parts ballast with 1 part cement, add water until you have a pour-able mixture. Allow the mix to set for 2 days minimum.
To build block or brickwork, you need to make a load of 'mortar' - see the table to choose the correct mixture. Remember to insert a DPC (Damp Proof Course) about 30mm off of the floor, between the courses.
Starting from each end of your wall, build a small portion of the wall, then run a piece of string between what you have just built (this will give you a plumb line to use as a guide to keep your wall straight). Build the wall between the ends until you are up to the string, then build up the ends and move the string higher. Repeat this process until your wall reaches the desired height. Don't forget to keep a frequent check on the level of the wall with a spirit level!!
Sand is graded by its size and shape, and its important to get the right type of sand for the job (like anything in life!)
Sharp Sand - A course and gritty material, normally used with another aggregates for making concrete and floor screeds.
Soft Sand - Known as 'builders sand'. It has smoother particals and is of a finer grade than sharp sand. It is mixed with Cement to produce mortar, or render.
Course Aggregate - Course gravel or crushed stone between 5mm to 20mm in size. It is used to form concrete when mixed with sharp sand and cement
Ballast - Is a combined 'all in' aggregate, this is a mix of sharp sand and course aggregate, used for making concrete.