CEMENT
Choose
the right
Cement
A guide to selecting the right cement
for your building requirements
CONTENTS
Choose the
Right Cement
01
02
03
04
05
09
15
21
22
25
27
29
31
33
34
35
Introduction
What makes a
Good Cement?
Misconceptions
about Cement
Lafarge in
Malawi
The Lafarge
Group
Kumanga
Ordinary Portland
Cement
Building Tips
The Basics
Ordering & Estimating
Materials
Plaster
Mortar
Common Defects
& Foundation Tips
Wall Tips
Finishing Tip
Storing & Handling
of Cement
1
Introduction
CEMENT
What’s in a
Name?
In 76 countries around the world,
the Lafarge brand name stands for
leadership in building materials:
leadership that has been achieved
by applying the knowledge within the
Group to bring innovative products
and solutions to satisfy the needs of
our customers.
T
he Lafarge brand represents values that set trends in the industry
today and are an active commitment to sustainable development: so
vital for the well-being of future generations. Our values mean:
•
-
•
•
-
respect and nurturing for our diverse employees by providing:
equitable employment opportunities
development opportunities to encourage everyone to reach
their full potential
proactively translating our concern for the environment into
action plans for:
rehabilitating our quarries
reducing ʻgreenhouse gasʼ emissions through better
technology and innovative fly ash extended products
reducing the dependence of the cement industry on nonrenewable resources
social responsibility:
assisting the development of neighbouring disadvantaged
communities, by setting up learnership programmes, to
create a core of marketable skills
actively promoting closer long term relationships by
assisting in problem solving and demonstrating real concern
for the well-being of nearby communities.
2010 | YOUR GUIDE TO CEMENT | PAGE 1
CEMENT
What makes a
Good Cement?
At Lafarge, cement is not a commodity but the exciting
bond that enables the creation of luxury office blocks
reaching a mile into the sky, huge sports stadiums, graceful
bridges, massive dams, elegant sculptures or just a simple
dwelling that you can call home!
We involve ourselves in the work of architects and developers and
pioneer cements that extend the boundaries of design. We talk to
new construction entrepreneurs and DIY homeowners and innovate
more user-friendly, efficient products and support services. We work
at building long-term business relationships. We listen to the marketʼs
needs and innovate new products and services that differentiate us
from our competitors.
Our cements are designed to give you more:
•
•
Industrial control standards that ensure consistent high quality.
Product performance and handling properties that exceed your
expectations.
Lafarge products are backed by service:
•
•
Access to technical advice from our Sales Team.
Innovative general support service through our Customer Care Centre.
A word of advice from an experienced builder:
“Save on the cost of your building materials by good
control, never by lowering quality – it is a false economy!”
PAGE 2 | YOUR GUIDE TO CEMENT | 2010
CEMENT
Misconceptions
about Cement
Myth: “It says 50kg on the bag, so it must contain 50kg of
cement!”
Fact: It should contain 50kg but it is a case of ʻBuyer Bewareʼ!
Not all companies have accurate enough equipment or the
management systems to achieve this.
Buy a well-known brand name product. The Lafarge name
is your guarantee: our cement is certified by MBS which is
clearly marked on all our packaging, assuring buyers of the
mass of cement they have paid for.
Myth: “Cement extenders reduce the quality of a cement.”
Fact: On the contrary, research and development over the
last thirty years has shown that, formulated correctly,
quality extenders significantly improve many performance
characteristics of hardened concrete, while making concrete
and mortar mixes more user-friendly for the builder.
Myth: “Any cement will do for general construction work: just go
for the cheapest!”
Fact: Why risk having a poor concrete job? Ask your builderʼs
merchant for advice. A good quality branded cement can
make concrete and mortar mixes that are easier to mix
and place. The finished concrete is also stronger and more
durable.
Myth: “A good mortar depends only on how well you mix the
materials.”
Fact: Thorough mixing of the materials until a uniform colour
is achieved is always essential to avoid a patchy finished
appearance and areas of weak strength. However, a good
quality cement, makes mixing easier. The resulting more
workable, “buttery” mix leads to a higher work rate.
Myth: “The strongest concrete is made with pure cement, not the
cements blended with extenders.”
Fact: Properly cured concrete containing quality extenders
will achieve a more durable and higher ultimate strength
concrete.
2010 | YOUR GUIDE TO CEMENT | PAGE 3
CEMENT
The Lafarge
Name
The business of Lafarge meets the basic
human need for building materials.
Lafarge in Malawi trades as Lafarge Cement Malawi
Ltd, ISO 9001: 2000 Certified Company and produces
two reputable brands of cement namely: Ordinary
Portland Cement (OPC) and Kumanga Masonry
Cement.
Lafarge Cement Malawi Ltd is continually growing
from strength to strength because of the experience
and technical resources of the international group.
The company has well qualified people in research
and development in construction materials to ensure
that your needs are met by producing world-class
quality Lafargeʼs cement.
Locally, our Quality Assurance Department is
supported by the unique technical and laboratory
resources of Malawi Bureau of Standards (MBS) in
conjunction with European Prestandard
What a Lafarge Bag of Cement Means for You:
-
An assurance of quality and performance
-
A formulation that has benefited from the international Groupʼs
technical know-how to create an innovative, user-friendly product
-
A product designed to meet your needs: needs that have been
identified from our work with architects, engineers and everyone
in the construction process
PAGE 4 | YOUR GUIDE TO CEMENT | 2010
CEMENT
The Lafarge Group
Lafarge is the world leader in building materials, with top-ranking
positions in all of its businesses: Cement, Aggregates & Concrete and
Gypsum. The Groupʼs 90 000 employees in 76 countries, generated
sales in 2007 of Euros 17,6 billion (over R210 billion).
The Group is:
•
•
•
Customer focused
Concerned for peopleʼs well-being
Concerned for the future
Concern for the environment
Lafarge is the
only company in
the construction
materials sector
to be listed in the
2008 ‘100 Global
Most Sustainable
Corporations in the
World’
Lafarge combines its skills and technical resources
with the expertise of others for greater effectiveness in
the environmental control field:
•
Lafarge was the first industrial group to
enter into a worldwide partnership with the
environmental protection organization, WWF
(World Wide Fund for Nature).
•
Lafarge is a founding member of CSI (Cement
Sustainability Initiative) which actively promotes
responsible management and the worldwide
reduction of carbon dioxide emissions by the
industry.
•
Lafarge is co-chair of the “Energy Efficiency in
Buildings” Project, which works towards the
objective of zero net energy use in buildings.
Leading the way with technology
The Group technical resources include:
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PAGE 6 | YOUR GUIDE TO CEMENT | 2010
2
Kumanga
CEMENT
KUMANGA MC 22.5 X
Introduction
Kumanga: MC 22.5X is a masonry cement
that achieves superior workability, without air
entraining agents, manufactured from Portland
Cement Clinker, Gypsum and other additives
according to MBS 413:2002 (equivalent to
EN413-1).
The superior workability and normal 28 days’
strength development, in particular, make
KUMANGA the ultimate solution to the quality
demands of all bricklaying, plasterwork, floor
screed, pointing, brick & block making in large
construction projects as well as Individual
Home Builders (IHB).
Product Attributes
•
Nomenclature
X = Contains no air entraining agents
22.5 = Cement Strength
MC = Masonry Cement
•
Workability
This hydraulic binder produces very workable
‘buttery’ mortar and concrete mixes that
require less effort and are easier to place
•
Stability
KUMANGA mortar mixes have a better response
to vibration, filling formwork more completely
without aggregates falling to the bottom of the
pour before setting specifically in brick/block
making.
•
Bleeding
KUMANGA has improved water retention and
less bleeding for reduced cracking and better
finishes.
2010 | YOUR GUIDE TO CEMENT | PAGE 9
CEMENT
Product applications.
•
Masonry work: mortars, plasters and screeds
•
Brick and Block making eg. Stabilised Soil Blocks, Solid/Hollow Cement blocks, Hydraform Bricks
•
Soil stabilization in road construction
Advantages of the product
•
Easier mixing
•
More workable ‘buttery’ mixes for block/brick layers
•
Easier laying with higher work rate
•
Economic value to MHC
•
Less wastage during plastering and brick/block laying due to enhanced cohesion in the mixes
•
Cost differential between Kumanga & OPC is MK 300.00 per bag which cumulatively becomes a huge saving
•
50 kg Kumanga has bigger volume than 50 kg OPC hence bigger volume mixes for use in rendering plastering and masonry work.
Confidence
The most significant party in the construction industry: YOU, will get
everything you expect from Lafarge, the world-leading cement producer.
Our products undergo constant rigorous testing for customer satisfaction
guarantee. YOU may also request for weekly product quality certificates so
that you have confidence that KUMANGA will:
•
•
•
•
•
have consistent high quality performance
enhance your on site productivity
deliver beyond your expectations
produce superior finishing
give you effective back up service and technical support from our engineers.
PAGE 10 | YOUR GUIDE TO CEMENT | 2010
CEMENT
Recommended Volume Mix Proportions
TYPICAL APPLICATION
CEMENT
1 Wheelbarrow Load
(2x 50kg bags)
CEMENT
1 Wheelbarrow Load
(2x 50kg bags)
Note:
•
•
CONCRETE SAND
STONE
5 Wheelbarrow Load
Mortar for
bricklaying &
plastering
CONCRETE SAND
STONE
8 Wheelbarrow Load
Brick & Block
Making Mix
Use the same container for measuring materials in a batch
2 x 50 kg Pockets of Kumanga MC22.5 X are = 1 standard (65
litres) buildersʼ wheelbarrow
When Working With KUMANGA Masonry Cement
Mortar is a mixture of sand, cement and water which is used for bonding
bricks and plastering. Plaster is a decorative or protective coating to concrete
and masonry walls and concrete ceilings. When mixing mortar, firstly measure
your quantity of sand according to your mix proportions and pile it up on
a water holding surface, preferably concrete or metal, in a saucer shape
to avoid draining water (locally known as mtondo). It is advisable to use a
concrete mixer where affordable.
Before adding water to the sand piled up on the mtondo, add cement
according to the recommended mix proportions and mix thoroughly until
the dry mix has a uniform colour. Now you can add water slowly to small
portions of the dry mix according to your required volume.
Clay bricks absorb water from mortar mix resulting in poor adhesion and
subsequent cracking of plaster works. Wet clay bricks before laying them and
plastering. The walls for rendering plaster should be rough and free of dirt
for grip.
2010 | YOUR GUIDE TO CEMENT | PAGE 11
3
OPC
CEMENT
ORDINARY PORTLAND
CEMENT CEM I 32.5N
Introduction
Lafarge Ordinary Portland Cement (OPC)
is a general purpose cement developed to
have a wide range of concrete and mortar
applications from domestic to heavy industrial
constructions. OPC is manufactured according
to EN 197-1: 2000 Prestandards.
OPC is technical cement that combines normal
strength development and performance at all
stages with versatility and it is recommended
for high specification structures.
Product Attributes
•
Mechanical and physical properties
Compressive Strength MPa
Early Strength
Strength
Class
2 days
7days
32.5 N
-
>=
16.0
Standard Strength
28 days
>=
32.5
<= 52.5
Initial
Setting
Time
(Min)
>= 75
Soundness
(expansion)
mm
<= 10
Note: N in the strength class denotes normal early strength development
•
Workability
OPC produces very workable concrete mixes that achieve a minimum
setting time of 320 minutes which gives you ample time to work with your
concrete.
•
Stability
OPC concrete mixes have a better response to vibration, filling formwork
more completely without aggregates falling to the bottom of the concrete
pour before setting.
•
Bleeding
OPC concrete has less bleeding hence less sand streaking along the shutter
giving better off shutter finishes.
2010 | YOUR GUIDE TO CEMENT | PAGE 15
CEMENT
Product applications.
a)
Low Strength Concrete (15 MPa)
Suitable for mass concrete and unreinforced single storey foundations
b)
Medium Strength Concrete (25 MPa)
Suitable for reinforced or unreinforced foundations, slabs, footpaths, driveways as well as domestic & light industrial floors
c)
High-Strength Concrete (30MPa)
Suitable for reinforced concrete, heavy duty floors and precast items such as concrete flagstones.
Note: MPa = Mega Pascals: unit of measure of force/pressure per unit
area
Advantages of the product
•
It is suitable for high specifications projects
•
can be used for general cement applications
Confidence
The most significant party in the construction industry, YOU, will get
everything you expect from Lafarge, the world-leading cement producer.
Our products undergo constant rigorous testing for customer satisfaction
guarantee. YOU will have confidence that OPC will:
•
•
•
•
•
have consistent high quality performance
enhance your on site productivity
deliver beyond your expectations
produce superior finishing
give you effective back up service and technical support from our engineers.
PAGE 16 | YOUR GUIDE TO CEMENT | 2010
CEMENT
Recommended Volume Mix Proportions
TYPICAL APPLICATION
CEMENT
1 Wheelbarrow Load
(2x 50kg bags)
CONCRETE SAND
2 Wheelbarrow Load
STONE
2 Wheelbarrow Load
Reinforced
concrete
(suspended slab, water
tight concrete, heavy
duty undustrial floors)
CEMENT
1 Wheelbarrow Load
(2x 50kg bags)
CONCRETE SAND
2 Wheelbarrow Load
STONE
3 Wheelbarrow Load
Medium
Strength
Concrete
(driveway, light
industrial floorsunreinforced)
CEMENT
1 Wheelbarrow Load
(2x 50kg bags)
Note:
•
•
CONCRETE SAND
3 Wheelbarrow Load
STONE
4 Wheelbarrow Load
Home Concrete
(foundations, footing
domesic floors –
unreinforced)
Use the same container for measuring materials in a batch
2 x 50 kg Pockets of Kumanga MC22.5 X are = 1 standard (65
litres) buildersʼ wheelbarrow
2010 | YOUR GUIDE TO CEMENT | PAGE 17
4
Building Tips
CEMENT
Tips for success
•
Good Quality Materials
Cement: Kumanga Masonry Cement & Ordinary Portland Cement (OPC)
assures you of good quality and reliability beyond any reasonable doubt.
Sand: Clean good quality sand will help you achieve the desired finishing.
Sand should not be contaminated with silt, clay or organic matter lest your
plaster cracks
Water: Remember, the more the water you add, the weaker the concrete or
mortar. Always use clean, good quality water in the optimum quantity that
will give a good water:cement ratio and produce a workable mortar suitable
for rendering plastering and masonry work.
w:c ratio = mass of water / mass of concrete
w:c ratio
strength
STRENGTH as % of the
28 DAY STRENGTH
Protect and Cure
Keep all your concrete work wet for strength development for at least 28
days. Curing also avoids cracking. Gently spray your concrete work with
water or protect it with plastic sheets or wet hessian sacks to prevent it from
drying out.
100%
28-Days Moist Cured
75%
50%
7-Days Moist Cured
3-Days Moist Cured
Not Cured
AGE (Days)
CEMENT
THE BASICS
1.1
•
•
•
•
•
•
Know the deference between “cement” ,“concrete” “mortar” and “plaster”:
Cement is a manufactured dry powder used as a binding material for concrete, plaster and mortar
Cement is one of the raw materials used along sand and stone to make concrete
Concrete is a composite of all the materials (cement, sand, stone and water) mixed together
Mortar is a mixture of cement, sand and water.
Mortar is a workable paste used to bind construction blocks/
bricks together and fill in gaps between them to give strength and stability to a wall.
Plaster is also a mixture of cement, sand and water but is used as a decorative coating to concrete, masonry walls and concrete ceilings.
1.2
•
•
•
What quality of stone should be used in making concrete?
Stone should be clean, hard and have durable particles.
The actual source of stone is less important than the size of the particles.
Single-sized particles are more economical to use.
1.3
•
•
•
•
•
•
•
•
Is the quality of sand important?
Yes. The quality of sand has a very marked effect on the quality of concrete and plaster.
Sand with poor grading generally gives a mix that is less workable, less economical and less easy to bring a good finish.
Poor quality sand is the major cause of cracking in plasters
Sand should not contain excessive amounts of clay.
Excessive clay/fines in sand causes cracking and reduces strength of mortar
An excess of fines may lead to an excess of mortar on the surface but this type of surface will wear rapidly under traffic.
Lack of fines in sand results in a harsh concrete which is hard to compact and to bring a good finish.
Do not use sands that the fines may have been washed out.
PAGE 22 | YOUR GUIDE TO CEMENT | 2010
CEMENT
1.4
•
•
What is the best type of sand?
The best sands are “evenly graded” – they contain particles of a wide range of sizes; medium sizes predominates but the coarsest and the finest are also present.
Sand should be clean- grass, leaves, roots etc are harmful.
1.5
•
•
Did you know that Sand used for concrete is different from sand used for Plasters and Mortar?
Concrete - River sands give good workability for concrete as they often consist of hard rounded particles, free from clay and reasonably clean.
For plaster and mortar – soft/smooth, loamy and non- gritty sand
1.6
•
•
Is the actual source of sand important?
No. The actual source of sand is not a reliable guide to its quality.
Sand quality can only be determined only by making trial mixes.
1.7
•
•
•
How can you check suitability of sand?
Do a trial mix using: 5kg cement and 25kg of sand
With good quality dry sand, 5 litres water should be enough to give a good plaster mix
If more than 6 litres are needed: find better sand!
1.8
•
•
Does the quality of water used in concrete matter?
Yes. Drinking water is normally suitable for making concrete and mortar
Murky or dirty looking water e.g. from a borehole or dam, should be tested by a laboratory before it is used.
1.9
•
•
•
Does it matter which type of cement used? Of Course!!
All cements are NOT the same even if the description on the bag looks similar!
Each type of cement is manufactured for specific application
ALWAYS follow manufacturer’s instructions and recommendation to achieve the best results.
1.10
•
•
•
•
What factors should I consider in selecting type of cement?
The first consideration should always be the PURPOSE i.e where is it going to be used
The impact of the choice of cement on the cost of the application
The strength suitable for the application
If early strength gain is required to save time and money spent on labours and formwork
2010 | YOUR GUIDE TO CEMENT | PAGE 23
CEMENT
1.11
•
•
What is the best way to measure a batch of concrete i.e cement, sand and stone?
Weight batching is the preferred method but it requires more sophisticated equipment to ensure accuracy as such, batching by volume is generally used for small jobs and projects.
A standard builder’s wheelbarrow is normally used to measure the correct volumes of cement, stone and sand to make a required batch of concrete.
1.12
•
What is the volume of a standard builder’s wheelbarrow?
A builder’s standard wheelbarrow holds 65litres of material
1.13
•
•
•
How many bags of cement are equivalent to one standard builder’s wheelbarrow?
A bag of 50kg of cement is approximately 33 litres
Two Bags of 50kg cement are equivalent of 65 litres HENCE 2x50kg bags = 1 standard builder’s wheelbarrow.
On each bag of 50kg cement, a mixing proportion indicating:
=
1.14
•
•
1 Wheelbarrow Load
(2x 50kg bags)
In the absence of a standard wheelbarrow what other tool can be used?
Any other container/tool can be used such as a bucket, oil or paint drums but the rule is: “Always Use the same size container to measure all the ingredients!”
A shovel is NOT recommended to measure materials as you cannot judge the quantities accurately.
PAGE 24 | YOUR GUIDE TO CEMENT | 2010
CEMENT
ORDERING & ESTIMATING MATERIALS
1.
1.1
a.
b.
c.
CONCRETE
There are three grades/classes of concrete specified for general building work:
Low strength concrete (15MPa)
Suitable for unreinforced foundations (single storey only), mass fill, infill masonry.
Medium strength concrete (25MPa)
Suitable for unreinforced slabs or floors, reinforced slabs and foundations, footpaths and domestic driveways
High-strength concrete (30MPa)
Suitable for reinforced concrete, heavy duty floors and precast items such as concrete flagstones.
Note: MPa =Megapascals: the measure of force/pressure per unit area)
1.2
To order cement, stone and sand, it is important to calculate how much concrete you need.
1.3
1.3.1
1.3.2
1.3.3
Follow the following steps to calculate the area required to place concrete:
Measure : the depth or height, length and width of each element in metres
Multiply : Height x Length x Width(measured in metres) = Volume of concrete required in cubic metres (m³)
Add : volume of each element together using the recommended mixing proportion to calculate amount of material to order
1.4
ALWAYS REMEMBER :
1m³ = 1,000 litres
m³ = length x height x width
1 Standard Wheelbarrow = 65 litres
2 Bags of 50kg cement = 1 Standard Wheelbarrow
Table 1: One cubic metre of concrete using 19mm stone (Typical stone)
CEMENT
CONCRETE SAND
Litres Wheel-barrow
STONE
m³
Litres Wheel-barrow
m³
5.8
650
10
.65
650
10
.65
Low Strength , 10-15MPa
7.7
620
9.5
.62
620
9.5
.62
Medium Strength 20-25MPa
600
9
.60
600
9
.60
High Strength 25-30MPa
9.2
2010 | YOUR GUIDE TO CEMENT | PAGE 25
CEMENT
1.5 Tips on Mixing Concrete
Always stick to recommended mix proportions – be accurate and consistent
•
Work on a clean, hard surface such as concrete floor or metal sheet
•
Do not mix concrete directly on the ground:
•
The mix will become contaminated with soil
•
The ground absorbs mixing water from the fresh mix, affecting workability and potential
•
The time from mixing the materials to the placing of the concrete should not exceed 45 minutes. If there is going to be delay, cover the concrete with plastic.
•
If there has been an unavoidable delay before placing the concrete and it resists being turned over a few times with a spade, than it has started to setting.
•
Do not try to weaken the concrete by adding water. It is better to make a new batch.
1.6 Tips on Common Applications of Concrete
Domestic Foundations
•
The performance of concrete floor on the ground depends on underlying material providing support.
•
Provide a carefully compacted 100-150mm thick layer of suitable fill material immediately below the concrete.
•
Finish the surface of this foundation layer smoothly.
•
Where the foundation is wet, dampproofing is necessary. Cover the foundation with polyethylene (plastic) sheeting.
•
The plastic prevents the concrete from absorbing moisture from the ground below.
•
Immediately before placing the slab, carefully and thouroughly dampen any foundation or adjacent part of the building not covered with plastic sheeting to prevent absorption of moisture from the concrete.
Floor Slabs
•
Concrete floor slabs for domestic or light duties should be at least 100mm thick
•
Do not lay panels larger than 3m² but where rectangular panels are required the length to width ratio should not exceed 1.25.
•
After placing the concrete, keep the slab covered for at least for at least 7 days to attain full strength and minimize any tendency to crack.
PAGE 26 | YOUR GUIDE TO CEMENT | 2010
CEMENT
•
•
•
•
•
•
•
•
•
•
•
Screeds and Toppings
A screed is a layer of well-compacted material (cement, coarse sand and water) applied to a floor slab.
The thickness of screeds should not be more than 30mm
A topping is a layer of concrete designed to provide a dense, abrasion resistant surface
Common cause of cracking in concrete floors is poor bond between topping and base course – always ensure a full-depth concrete slab.
Preparation of the surface is of utmost importance to achieve a good bond
Chip the surface and remove all dust and debris
Absorptive surfaces should be soaked to ensure water is not drawn from the screed mix to the surface floor.
Pour the concrete in panels not more than 30mm thick and 3m²
Domestic screed mix is 1:4- using river or pit sand i.e (2 50kg Bags and 4 wheelbarrows)
Do not sprinkle cement powder on the surface to absorb bleed water or to improve finish – the surface will be prone to crumbling and scaling
Do not sprinkle water on the on the surface or finishing
1
PLASTER
1.5
Plaster is the mixture of sand and cement.
1.6
Sand-cement plaster is used a decorative or protective coating for internal and external walls, concrete ceilings and reservoirs.
1.7
•
•
•
•
Tips on plaster and plastering:
Freshly mixed plaster should be uniformly mixed, easily workable and have good water retention.
The receiving surface should be rough and free of dirt, dust and flakes of paints. Roughness improves adhesion by providing a positive “key” for plaster to grip.
Do not make more plaster than can be used in 2 hours. Mix small batches as required. Trying to restore its workability with water will not give satisfactory plaster.
If plastering work is done in direct sun, it should be protected from sun and drying winds for at least 7 days. Periodical watering, covering by wet sack or plastic sheeting and sand application are among means of achieving protection.
2010 | YOUR GUIDE TO CEMENT | PAGE 27
CEMENT
1.8
•
•
•
•
Sand Quality is important for plasters:
Poor quality sand is the main cause of cracking in plasters
Pit sands are often the best for plasters
The sand should not have excessive amounts of clay - too much clay requires high water content.
Always remember: source of sand is an indication of quality.
1.9
•
•
•
Workability
Builders lime may be added for improved workability if sand lacks fines or is single sized. Use a maximum of 40 litres of building lime per 50kg of cement.
Do not use lime to replace cement- only as an addition to cement.
Test for workability by tilting the trowel: a good workable mix will slide off. If it sticks to the towel, the sand contains too much clay.
1.10
Estimating Quantities
1.10.1 Materials for plaster can be estimated by area i.e. m²
1.10.2 To plaster an area of 8.5 m², please follow the recommended mix proportions shown below.
RECOMMENDED PLASTER MIXES
CEMENT
1 x 50 Kg Bag
CEMENT
1 x 50 Kg Bag
CONCRETE SAND
1.5 x Wheelbarrow Load
CLASS I
Plaster recommended
for highly stressed
units and areas
exposed to dampness
(reservoirs swimming
pools etc)
CONCRETE SAND
2.5 x Wheelbarrow Load
PAGE 28 | YOUR GUIDE TO CEMENT | 2010
CLASS II
Commonly used
plaster (Internal &
External Walls,
Ceilings)
CEMENT
2
2.5
MORTAR
Mortar is also a mixture of cement and sand but it has the following main functions:
2.5.1
Bond bricks/blocks together and help resist sideways forces
2.5.2
Provide an even bed to distribute the load on the wall
2.5.3
Seal the joints against rain
2.6
Mortar should be readily workable to allow the block/
bricklayer to produce satisfactory work at a rapid rate.
2.7
•
•
•
•
•
•
•
•
•
Tips on working with Mortar:
Mortar should be soft, plastic and must spread easily
It must be thoroughly mixed to a uniform colour
Sand should be clean and not have too high a clay content
Joints should be as thin as possible. Thick layers are wasteful in mortar.
Do not make too strong a mortar as it is unnecessarily costly and could lead to cracking
Do not make more mortar than could be used in 2 hours. Trying to restore workability by adding water weakens the mortar.
If mortar has to be left in the sun before being used, cover with plastic sheeting or wet sack.
Clay bricks should be wet for laying
Cement bricks or blocks are laid dry
2.8
What is the quality of a good brick?
Check and examine the bricks to be used in a building before they are laid
in the wall and they should meet the following requirement:
•
They should be sound free from crack or flow and from stone and lumps of any kind especially pieces of line
•
The brick must be uniform in size, with sharp angles and edges, and the surface true and square to each other, this insure neat work
•
Good building brick should be quite hard and well burned. A simple and generally satisfactory test for common bricks is to strike two of them together, or to strike one with the edge of a mason’s trowel, if the brick give a ringing sound it is generally sufficiently strong for any ordinary work. A dull sound shows the brick is soft or shaky
2010 | YOUR GUIDE TO CEMENT | PAGE 29
CEMENT
•
The quantity of water absorbed is also important. A good brick should not absorb more the one tenth its weight in water. A good test is to weigh the brick first then immerse it in water for 24 hours and weigh it again. From the increased in weight, the percentage of water it has absorbed may be found. Very soft under burned bricks often absorb from 25 to 35 percent of water. Weak light red brick, often used in filling the interior of walls, will absorb about 20 to 25 percent while the very best brick may absorb not more than 5 percent and should , if possible be used for outside walls and foundation wall and piers
2.9
•
•
•
Did You Know?
The strength of an ordinary brick is 5MPa
Bonding bricks with mortar having strength of around 5 MPa or slightly more (which you easily get when Kumanga is used) gives satisfactory results.
Due to elastic nature of ‘too strong mortar’ if used as binder for ordinary bricks, cracking is enhanced.
2.10
Estimating Mortar Quantities
2.10.1 To lay 1000 bricks use:
•
•
3 Bags of Kumanga cement and 9 wheelbarrow loads of sand (.6m³)
REMEMBER: 50 normal clay bricks make up one square metre
RECOMMENDED MORTAR MIXES
CEMENT
2 x 50 Kg Bag
CEMENT
2 x 50 Kg Bag
CONCRETE SAND
4 x Wheelbarrow Load
CLASS I
Mortar recommended
for damp course or
load bearing brickwork
CONCRETE SAND
6 x Wheelbarrow Load
PAGE 30 | YOUR GUIDE TO CEMENT | 2010
CLASS II
Commonly used
mortar for normal
load- bearing
applications
(laying bricks and
blocks)
CEMENT
COMMON DEFECTS
1.
a.
•
•
Peeling off of plaster
What causes peeling off of plaster?
Non-complying materials i.e unclean sand & cement
Incorrect mixing ratios i.e adding too much sand in a mortar material mix.
b.
•
What is the Remedy?
Adhere to design mix ratios while using complying materials and re-plaster.
2.
a.
•
•
•
•
Cracking
What causes cracking of walls
Poor workmanship of brick laying
Use of weak or partially broken bricks
Mortar ‘too strong‘ as a binder for a particular quality of bricks
Laying clay bricks while very dry and failure to periodically moist the binding bed of mortar.
b.
•
•
•
•
What is the preventive measure
Professional brick laying hence Umisili initiative by Lafarge Cement Malawi
Avoid using partially cracked bricks during brick laying
Avoid use of ‘too strong mortar’ as binder for ordinary bricks. Mortar made from Kumanga is the most appropriate for brick laying
Wet clay burnt bricks before use and periodically spray water to the binding bed of mortar (at least for one day).
FOUNDATION TIPS
A poor
•
foundation will sentence your house to an early grave…
Set out the layout of the house or structure to be built in accordance with the site layout drawings. Make sure that you closely observe the depths of excavations indicated on your drawing
•
Choose a well known and trusted brand of cement for your project i.e. Kumanga cement found at Lafarge Cement Malawi and all its appointed agents and distributors is the best cement for all your brickwork
2010 | YOUR GUIDE TO CEMENT | PAGE 31
CEMENT
•
Identify a source of good quality sand and quarry, refer to our basic tips to know how you can identify good quality sand and quarry
•
Identify a skilled and well trained builder especially under the Lafarge Cement Umisili program. To get hold of such builders near your area, please contact Lafarge Cement offices for more information
•
To have a stable base for the foundation, use Kumanga cement to make concrete. To achieve suitable strength use a mix proportion of 2 bags of Kumanga cement, 2 wheelbarrows of sand and 3 wheelbarrows of quarry (stone). Mix this with 30 liters of water (one and a half pale of water)
•
Firstly measure and pile aggregate on your mixing surface. Then measure your required sand amount and pile it on top of the aggregate. Before adding water, pile your cement on top of the aggregate and sand and then dry mix it until the whole mix has a uniform colour. Now you can start adding water and continue mixing your small portions. If you have access to a concrete mixer, then your job becomes easier for you.
•
Pour the concrete on the excavated floor of the foundation. The thickness of the concrete must be 75mm throughout the foundation. This is called the blinding layer and is very important since it provides a more stable base for the foundation and hence reduces settling of the structure
•
After the blinding layer has cured and hardened (at least 2 days after casting), start construction of the foundation walls with good quality bricks, refer to our basic tips to know how you can identify a good quality brick
•
Prepare a Class III mortar mix. To achieve this measure 2 bags of Kumanga cement against 8 wheelbarrows of well graded sand. Please note that 2 pockets of 50 kg Kumanga MC22.5 X are equal to 1 standard (65 litres) builders’ wheelbarrow.
Remember, the strength of your mortar depends on your water:cement
ratio, more water, less strength!
Settling is the periodic sinking of the structure or house. The total allowable settling for a structure is 20mm or
less. Settling of more than 20mm causes the structure to be unstable and to crack or even collapse
PAGE 32 | YOUR GUIDE TO CEMENT | 2010
CEMENT
•
Once a Class III mortar mix is prepared with a qualified Umisili builder, build the foundation wall. Make sure it is well leveled and positioned as per the drawings
WALL TIPS
A well built brick wall must have a footing sized for proper support
•
Choose a well known and leading branded masonry cement. Kumanga cement is just the best cement from Lafarge Cement Malawi that was tailor-made to meet perfectly your masonry requirement
•
Identify a clean and good quality sand for your mortar mix
•
Identify a source of good quality bricks
•
Source a well trained and knowledgeable builder in your area, preferably, one who has been trained through the Umisili program by Lafarge Cement Malawi
•
Brick wall are intended to be laid as a veneer wall (meaning against another wall, like on a house)
•
•
Make sure you have all the tools that will be needed
Start by putting a brick down at each end of where you want the wall to go. Don’t put any mortar down yet. Measure from the outer edge of the brick at one end to the outer edge of the brick at the other end to get the length of the wall
•
Now that you have measured you can start laying bricks at both ends. Prepare a class III mortar mix. To achieve this measure 2 bags of Kumanga cement against 8 wheelbarrows of well graded sand. REMEMBER, THE STRENGTH OF YOUR MORTAR DEPENDS ON YOUR WATER:CEMENT RATIO, MORE WATER, LESS STRENGTH. Put your level on top of them and make sure the bricks are level. Measure away from the wall on both ends of the bricks that you just laid. Put your level against the face of the bricks to make sure that they are straight
•
After you have a couple of courses laid on both ends, hook a line up at both ends, so it lines up with the very top of the bricks. Now you can go through the middle and lay every brick to the line
2010 | YOUR GUIDE TO CEMENT | PAGE 33
CEMENT
•
Keep laying your ends up then fill in the middle till you get to your destined height. Make sure you check with a level in the middle of the wall time and again to make sure that it is staying level. If one side gets too high, lay the bricks tighter on the end.
FINISHING TIPS
The aesthetics of your home is primarly dependant on the quailty of your
finish - so get it right:
•
•
•
•
•
Plastering
Pointing
Floor
Drainage
Driveway
PAGE 34 | YOUR GUIDE TO CEMENT | 2010
CEMENT
Storing and
Handling Cement
Before handling cement, take a moment
to look at the top priority in any task - the
Safety issues:
Cement is such a commonly available product that
many people will have used it without giving any
thought to their personnel protection. Although
cement poses little immediate hazard, it is important
to take sensible handling precautions.
Personal Protection
Suitable protective equipment (goggles, masks,
boots and gloves) and clothing should be worn
during the handling of wet or dry cement.
Storing Bags of Cement
Cement is designed to react strongly with
water and go hard, therefore:
Protect bags of cement from rain, moisture
in the ground and moisture from the air.
Preferably store pallet loads and loose bags
in a warehouse or weatherproof shed:
- keep loose bags off the ground/floor. (Use
plastic sheeting or spare pallets)
- stack pallets only two high (three high is
unstable and will be a SAFETY HAZARD)
- close windows and doors to stop damp air
blowing over the bags
Stored cement must not be
exposed to moisture
- make tidy stacks with wide aisles so that
forklifts do not tear the bags
2010 | YOUR GUIDE TO CEMENT | PAGE 35
CEMENT
If material has to be stored outside:
Preferably cover palletised loads with a waterproof
tarpaulin to provide additional protection against the
elements. Stack loose bags on a platform of spare
pallets or timber slats covered in plastic sheeting:
- Cover the bags with sheeting
- Create a ridge for the sheeting so that rain runs off
- Weigh down the edges of the sheeting with stones
or timber to prevent winds blowing it away
Planning your stacks:
Arrange your stacks so that the first-in
cement can be the first out (FIFO). This is
important because even well-stored cement
will begin to deteriorate after approximately
3 months.
Do not store cement next to products such
as gypsum-based building materials,
fertilisers or other chemicals. Small amounts
of contamination can cause a big problem
with the cement.
Handling Bags of Cement
Forklift drivers should be made aware of the cost of
bag breakages. A breakage means cement is lost and
time is also lost clearing up:
- Bags should be staked under cover on spare pallets
on a flat, level area that has been checked free of
sharp objects
PAGE 36 | YOUR GUIDE TO CEMENT | 2010
CEMENT
Lifting should be carried out with the forklift
tines parallel to the floor to avoid
overstressing the pallet.
Remember:
Manual handling must be done carefully to
avoid damaging the bag or injuring the
handler:
- not to overload the forklift (many forklifts
are only deisgned to lift one pallet at a time)
- Do not drop bags of cement from head
height or from the bed of the truck
- not to damage the wooden slats or the bags
when inserting the forklift tines into the
pallet
- to stack the top pallet neatly on the bottom
one
- Persons who are not trained to handle
cement bags (usually 50Kg) can easily hurt
their backs when lifting or manhandling full
bags by themselves. Lifting should
preferably be done by two people.
- Lift bags by bending the knees and keeping
a straight back to minimise the chance of
back strain.
- Always lift a bag by putting hands
underneath to support it, never by holding
the ends. This bends the bag and can cause
the bottom to tear open.
2010 | YOUR GUIDE TO CEMENT | PAGE 37
CEMENT
- Always roll a bag over before lifting it.
Check the underside of any damage. Rolling
also loosens the cement and reduces the
chance of the bag splitting.
- Never drag a bag over a pallet, a floor or
bed of a truck. Instead always roll it.
- Never walk on the cement bags.
PAGE 38 | YOUR GUIDE TO CEMENT | 2010
CEMENT
Lafarge Cement Malawi Ltd.
Makata Heavy Industrial Area,
P.O. Box 523, Blantyre, Malawi.
Tel: +(265) 1 870 031
Fax: +(265) 1 871 026
www.lafarge.com
September 2010