BT 202 Lecture 6 Masonry Construction Mortar

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BT 202 Lecture 6Masonry ConstructionMortar
Lecturer Leonie Matthews Rm 630 T
92662715 Email l.j.matthews_at_exchange.curtin.edu.a
u
(The BDA Guide to Successful Brickwork, 2000, 2nd
ed )
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Mortar

• Suitably proportioned mixture of sand, cement
  /or lime, water, with or without additives or
  chemical admixtures
• Bonds units together provides overall
  soundness
• Provides a construction method that makes
  possible the wide variety of forms, textures
  patterns characteristic of masonry

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Functions of Mortar

• Accommodates variations in unit sizes shape.
• Generally joint thickness 10mm
• Provides adhesive bond strength - sufficient to
  resist lateral loads provides overall
  robustness
• Even bedding of units sufficient strength to
  resist compressive loads
• Provides a weather-tight durable wall by
  sealing the joints between the units.
• Provides aesthetic effects by various joints
  treatments, pigmentation, bonding patterns.

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Important Properties of Mortar

• Consistency
• Durability
• Ability to bond with masonry units
• All of these can be significantly affected by
  workmanship site practices

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Workability

• Best left to the bricklayer (testing methods
  generally only useful for research purposes
• Difficult to use mortar that is too wet or too
  dry
• The most suitable mortar for the bricklayer will
  usually impart the best qualities to the masonry.

(The BDA Guide to Successful Brickwork, 2000, 2nd
ed )
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Water Retentivity

• When wet mortar masonry units come into contact
  certain amount of water sucked into units. This
  movement is beneficial to bond, but shouldnt be
  so great as to leave mortar with insufficient
  moisture for proper setting.
• The ability of mortar to retain sufficient water
  against the suction of the unit is called water
  retentivity.
• Good water retentivity provides three benefits
• Limits the bleeding of water from the mortar
• Prevents rapid stiffening of the mortar-bed
  before units are laid for the next course.
• Retain sufficient water in the joint for
  hydration of the cement

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Control of Water Retentivity

• By the choice of
• appropriate sand grading
• mortar composition eg. Mixes with a higher
  proportion of lime

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Durability

• As important as strength (mortar classification
  AS3700)
• Influenced by joint finish
• Durability increases as cement content increases

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Bond Between Mortar Units

• More important than compressive strength
• Determines the strength of wall against wind
  earthquake its general serviceability
• Failure of masonry walls more likely to be from
  lateral loads, particularly wind, than vertical
  loads

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Tensile Bond Strength

• Affected by mortar type
• Enhanced by the presence of lime
• Reduced by workability admixtures
• Doesnt necessarily increase with increase of
  cement content

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Factors Affecting Bond Strength

• Sand grading - an excess of clay particles will
  reduce bond strength
• Brickies sand has high clay content that
  improves workability. However, if clay content
  too high bond strength can be compromised.
• Use of admixtures can reduce bond strength
• Cement hydration

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Composition

• Traditionally specified in a prescriptive way by
  giving proportions of cement, lime, sand
  (cls)
• Classification system of AS3700 comprises of
  grades M1, M2, M3 M4
• Most masonry in housing small-scale structure
  with mild exposure uses M2
• General work loadbearing walls use M3.
• M4 used for applications where high compressive
  strength or high durability required
• M1 mortar used in heritage or restoration work

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M3 Mortar Deemed-to-satisfy (AS3700)
116 Portland cement 15 Portland cement (
water thickener) 115 Blended cement 14 Blended
cement ( water thickener 14 Masonry cement
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Materials

• Cement
• Lime
• Sand
• Water
• Admixtures

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Cement

• 3 Types of cement commonly used in Australia
• General Purpose (Type GP) most common, suitable
  for
• high quality work
• load bearing walls
• Consists primarily of Portland cement
• Blended cements (Type GB)
• Portland cement with fly ash or blast furnace
  slag
• Masonry cements
• Portland cement fly ash, blast furnace slag,
  finely ground limestone, building lime,
  plasticisers air entrainer. Manufacturer must
  demonstrate performance compliance with
  requirements of AS3700 particularly strength.

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Blended cements masonry cements cannot replace
Type GP cement in same proportions. Generally
give slower strength development lower final
strength.
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Lime

• Properties
• plasticity
• self healing of minor cracks throughout life
• good bond with clay units
• reduction in speed of hardening, masonry can
  take up minor movements during construction
• generally used as a dry hydrated lime (powder),
  added to mortar during on-site mixing.
• Is available in putty form but this is generally
  used for finishing work eg. hardwall plaster
• Mortar below ground should not use lime, rish of
  reaction with soil.

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Sand

• Clean free of salts organic matter
• Graded so doesnt contain too much clay and has
  variable particle sizes.
• Small amounts of clay improve workability
  avoid the need for proprietary plasticisers

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• Sand Grading
• of sand passing through a standard set of
  sieves
• Grading limits used as a guide only. Experience
  is the best guide
• Generally accepted limit for good masonry mortar
  with clay units is that sand should not contain
  more than 10 passing 75-micron sieve not more
  than 1 retained on 2.36mm sieve
• For concrete calcium-silicate units sand
  should be clean sharp, used with water
  thickener (methyl-cellulose type)
• Problems of high clay content
• Staining
• reduced mortar strength
• sticky mortar mix
• durability
• workability

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Water

• Lubricant that allows other materials in mortar
  to be brought to a workable consistency
• Water should be free of suspended fine particles
  dissolved salts or other compounds.
• Test for suitable water potable drinkable
• Water brings about hydration of cement
  responsible for tensile compressive strenghts
  durability.

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Admixtures

• Inappropriate use of admixtures in masonry mortar
  is a very common source of problems. Most common
  is over-dosing of air-entrainers leading to
  extremely low bond strength.
• AS3700 restricts use, the following are
  permitted
• Plasticisers air-entraining agents improve
  workability. Air-entrainers air bubbles behave
  like ball bearings increase workability.
  However, reduces contact between the masonry unit
  the mortar thereby reducing bond strength.

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• Methyl-cellulose water thickeners improve water
  retentivity (for use with concrete calcium
  silicate units
• Colouring pigments
• Set-retarding agents
• Bonding polymers enhanced bond strength, not
  widely used in Australia
• Admixtures such as polymers workability agents
  should not be used as a substitute for lime.

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• Admixtures for colouring synthetic metal oxides
• Mixed with cement to for, a pigmented slurry that
  coats saind grains.
• Generally no more than 10 pigment ( by weight of
  cement) will not increase colouring
• Carbon black must not be added in proportions
  greater than 3 by weight of cement.
• Pigments adds to total fines content of mix
  therefore can affect workability water
  retention (hence bond strength)
• Liquid suspensions convenient but liquid medium
  may be air-entraining agent.
• Fading of pigmented mortar can occur. General
  causes
• too little cement
• over-use of air-entraining agents
• degradation due to aggressive atmosphere or
  moisture
• staining due to efflorescence or chemical
  deposits

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(The BDA Guide to Successful Brickwork, 2000, 2nd
ed )
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Waterproofing Additives
Should not be relied upon as a substitute for
membrane damp-proof courses unless strong local
evidence that foundation movements very small
admixture has proven history of reliable
performance. Any crack in mortar will destro the
water-resisting effect. Excessive use results in
reduce strength of mortar.
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Curing
Unlike reinforced conc. curing of masonry not
common on site. Generally mass of constructed
masonry cavity ensures a sufficient degree of
curing. Masonry needs to be protected on site
from drying out too quickly in hot
conditions. Design strength based on 7 days
assumes normally rate of strength development. If
drying out interupts this development then
required strength may not be achieved.
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Mixing
To achieve appropriate mortar composition on site
batching method needs to be accurate. Most
commonly used is shovel batching but this is the
least accurate. Different bulking properties of
sand, cement lime.
www.brickbydesign.com/teach.html 2004,
September 6
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Volume batching buckets of guage boxes avoids
this problem. Best method Bagged cement lime
in correct quantities to a mixer of known volume
then fill with sand. Volume calculations are
straight forward will not change once
established for a mixer.
www.brickbydesign.com/teach.html 2004, September
6
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• Mixing time
• Min 6 minutes (no max)
• Mortars with air-entrainers should not be over
  mixed. Too much air.
• Mortars should not be used once setting has
  commenced. Initial set usually one or two hours
  after mixing depending on conditions.

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Grout

• Protects reinforcement from corrosion.
• To achieve this must completely surround bars
  contain sufficient cement to provide a protective
  alkaline environment.
• Grout must be mixed to a pouring consistency to
  ensure that bars in all pockets, cores cavities
  are fully surrounded.
• Although high water content gives lower strength
  for grout important factors are
• complete filling of the cores
• units absorb much of the water, reduces
  watercement ration gives improved bond
• Increase in strength of grout beyond strength of
  unit gives small increase in strength of masonry
  assembly.
• AS3700 grout 12MPa compressive strength

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3
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After mixing mortar placed on mortar boards.
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Storey rod (storey pole or gauge rod)used to
set out the vertical heights of brick or block
courses. Ensures uniformity of heights for entire
job. (Milton, H., 1994)
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• String line to maintain horizontal bedding line.
  String line held in place by corner block.

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(The BDA Guide to Successful Brickwork, 2000, 2nd
ed )
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Joint finish using a chariot jointer
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Concave joint or ironed joint
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Concave joint or ironed joint
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1
Brick commons delivered to site
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Bolster for cutting bricks
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• Brickwork tools ( clockwise) trowel, gympie, cold
  chisels, cramps, jointer, bolster, chariot
  jointer, string line pin.

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References
Lawrence, S. 2001, Construction Guidelines for
Clay Masonry, CBPI, NSW. The BDA Guide to
Successful Brickwork, 2000, 2nd ed, The Brick
Development Association, London. CBPI Masonry
Teaching Package April 2000 online, Available
www.brickbydesign.com/teach.html 2004, September
6
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Slides
Slides 1-13 Shinners, N. Slide Collection Slides
14,15 Molinari, L. 1998, Mario Botta Public
Buildings 1990-1998, Skira editore, Milan
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