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!
Brick
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
10mm.
When
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 ‘m^{2}’ 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’.
These
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.
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2. CHOOSING MORTAR MIXES FOR BRICKWORK
Type
of Construction 
Proportion
of Cement / Building Sand 
External
walls above DPC 
1
part cement : 5 parts sand 
External
walls below DPC 
1
part cement : 4  5 parts sand 
Internal
walls &inner leaf cavity walls 
1
part cement : 6 parts sand 
Coping
stones and sills 
1
part cement : 3 parts sand 
Parapets
and chimneys 
1
part cement : 4  5 parts sand 
Retaining
walls 
1
part cement : 3 parts sand 
External
free standing walls 
1
part cement : 4  5 parts sand 
Manholes 
1
part cement : 4  5 parts sand 
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3. CHOOSING MORTAR MIXES FOR BLOCK WORK
Type
of Construction 
Proportion
of Cement / Building Sand 
External
walls above DPC 
1
part cement : 6 parts sand 
External
walls below DPC 
1
part cement : 5 parts sand 
Internal
walls 
1
part cement : 6 parts sand 
Parapets 
1
part cement : 6 parts sand 
External
free standing walls 
1
part cement : 5 parts sand 
Manholes 
1
part cement : 5 parts sand 
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4. MEASURES TO CREATE CONCRETE
Number
of bags of cement 
Number
of bags of ballast (50Kg) 
Amount
of Water in litres 
Produces
this amount of concrete... 
1 
12 
37 
0.25
cubic meter 
2 
24 
74 
0.5
cubic meter 
3 
36 
104 
0.75cubic
meter 
4 
48 
150 
1
cubic meter 
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5. CHOOSING MORTAR MIXES FOR RENDERING
Background
material 
Proportion
of Cement / Building Sand 

Undercoat
¦ Top coat 
Low
suction bricks / blocks /stone 
1cement: 3 sharp sand
¦1cement: 5 sharp sand 
Normal
suction bricks (clay etc) 
1cement: 5 sharp sand
¦1cement: 6 sharp sand 
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6. Right! you've sorted the materials, how do you
build it?
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 pourable 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!!
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7. Construction of a wall  how to keep it level...
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8.
Different types of sand
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.
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