Mortars and Plasters

Mortars and Plasters

BUILDING CONSTRUCTION MATERIALS

Mortars

• Building mortars are mixtures, used for the joining of bricksand stones.

• Definition: A paste obtained by adding water to amixture of fine aggregates such as sand and bindingmaterial.

• The pyramids of Egypt have been built with clay-gypsum, gypsum-lime and lime mortars.

• The safety, strength and durability of resulting wall orany structure depends on the quality of the mortar usedas a binding medium.

• Plaster: It is a lean mortar that has been prepared forthe specific use of providing a protective covering on theinner or outer faces of construction

Mortars

The Pyramids Of Egypt Have Been Built With

Clay-gypsum Mortar

Functions

• It provides binding force or cohesion betweenthe structural units.

• It act as a medium for distributing the forcesthroughout the structure uniformly.

• Additional strength and resistance against rainpenetration and other such weathering agencies.

• In stone or brick masonry, it fills up emptyjoints; a thin liquid mortar used for suchpurposes is termed as grout.

• It does pointing or plastering to the structure.

Functions

Qualities Or Properties Of Good Mortar

• The mortar mix should be easily workable – easily

transported to the place of application.

• It should develop adequate strength in tension,

compression and bond for the work for which it is

used.

• It should be sufficiently plastic – easily placed on

the bed of construction in the form of thin, smooth

and uniform layer.

• It should be capable of retaining sufficient water

during its application.



• It should be durable and strong in itself on dryingand hardening and at the same time, it should notreact in any way with the construction units.

• It should set and harden quickly – construction couldbe done with speed.

• It should not develop any cracks on drying andshould be able to maintain their appearance for quitea long period.

• It should be capable of developing the designedstresses.

• It should be economical to make withoutcompromising on any of the qualities.


Classification Of Mortars

• Based On Types Of Binding Material

depending on the nature of the job – mortar maybe made by using one or more cementingmaterials.

• Lime Mortar are mixture of fat lime or hydrauliclime, sand and water.

• Fat Lime – requires loss of moisture – notsuitable for construction in damp and moistconditions, suitable only for thin joints inbrickworks Light colour, do not causeefflorescence

Lime Mortar

Classification Of Mortars

• Hydraulic lime – suitable for damp situations.

• Cement Mortar are prepared from Portland cement or itsvarieties, sand and water.

• Surkhi Mortar: ordinary type of mortar where sand ispartly or wholly replaced by surkhi (crushed burnt bricks)in lime mortar.

• The ratio of lime to surkhi will depend on the nature ofjob.

• It can not be used to make mortar with cement – it isreactive to some cementing materials.

• Commonly used in foundation works.

Cement Mortar

Surkhi Mortar

Based On Types Of Building Material

• Gypsum Mortars are prepared from gypsums oranhydride binding materials.

rarely used in tough construction – application asplasters.

• Gauged Mortars are prepared by adding Portlandcement and lime together in properly determinedproportions as binding materials.

Stronger, denser and durable than ordinary limemortars.

• Composite Mortars: may be surkhi-motar (surkhi,lime and water), lime-surkhi-sand mortar, cement-limemortar and cement-clay mortar.

Gypsum Mortars

Gauged Mortars

Based on Nature of Application

• Brick Laying Or Masonry Mortar: mainmortars used as binding medium between thebrick masonry units in the construction offoundation and walls.

• Finishing Mortars Or Plasters: are leanmortars used for protective covering overwalls and also in ornamental work and forarchitectural purpose.

It should be homogeneous mix.

Brick Laying Or Masonry Mortar

Finishing Mortars Or Plasters

Based On Density Of Mortar

Heavy Mortars: Bulk Density – greater than 1500 kg/m3.

• Aggregate - Heavy quartz or sand.

• Use in load bearing constructions

• Special type of heavy mortar – X-rays shielding mortars -Bulk Density – 2200 kg/m3 or more.

Light Weight Mortars: Bulk Density – less than 1500 kg/m3 .

• Aggregate – sands poorer in quartz and also crushedlightweight rock such as pumice, blast furnace slag.

• Use where structure is to be kept light loaded.

• Special type of Light weight mortars - Bulk Density – 600- 1000 kg/m3 – for making sound proof ceiling and walls.

Based On Density Of Mortar

Lime Mortars

• Definition: homogeneous mixes of lime with various

proportions of fine sand, surkhi, pumice, ash, in

water.

• Common mortar in ordinary type of building

construction work.

Lime Mortars

Lime Mortars

Preparation

a. Selection Of Raw Materials: lime, sand, surkhi,pumice, ash are common materials used in limemortars.

• Lime – binding material

• Sand – more commonly used – may be partly orwholly replaced one or more materials.

• Fat Lime: used in dry type of construction.

• Hydraulic Lime: used in water rich areas anddamp conditions.

Selection Of Raw Materials

• Sand: Good quality for making strong and durable

mortar – pure in composition and free from impurities

and sharp grained in structure.

• Purpose To Add Sand In Mortar:

• To bear the load – sand + lime (cement) = stone

like mass.

• To resist shrinkage and cracking.

• To increase bulk of the mortar.

Purpose To Add Sand In Mortar

Selection Of Raw Materials

• Pozzolana Materials: natural or artificial materials that exhibitssome binding properties when used with cement or lime. – pumice,cinder, surkhi and ash.

• Surkhi – finely grinding well-burnt bricks.

• Cinder – fine residue from the burning of coals in railwayengines.

• Suitable for making lightweight mortars.

• Pumice – natural highly porous volcanic rock formed byaccumulation and compaction of ash from volcanoes.

• Suitable for making lightweight mortars.

• Water: which is suitable for drinking purpose.

• Water should be free from alkalies, acids and organic residues.

Proportioning Of The Raw Materials

• Aim: to fix such ratios of the ingredients that gives amortar of desired qualities (strength, durability, finish andcost).

• Mortar used in different places in a construction are subjected todifferent forces – no general rule for proportioning a mortar mix canbe framed.

• Additional facts should also be remember while selecting ratio.• If more sand is added than recommended – short in workability,

difficult to place.

• If less sand is added than recommended – very stiff and will stick –show considerable shrinkage on drying.

• When In doubt – add a little more (not less)

• The amount of water - carefully fixed after trials – neither too lean andnor too stiff.

C. Mixing Of Raw Materials

Mannual Mixing: common method for ordinary construction.

• Done either on a watertight platform made of masonry or intank of suitable dimensions dug in the ground.

• First place measure volume of lime on platform and mix itproperly.

• Water is added in small quantities a time. Mixing iscontinued till a mortar of uniform consistency is obtained.

Mortar Mill Mixing: mechanical device for grinding themortar ingredients in the presence of water.

• Either run by an animal (lime chakki) or by motor power(grinding mill).

Mannual Mixing

Mortar Mill Mixing

Properties Of Lime Mortars

• Quite plastic and workable when wet

• Good working qualities if made from high calciumlimes

• Develop strength very slowly but gain continuousstrength over long periods

• Do not set but stiffen as water is lost by absorptionby units or blocks in contact and by evaporation.

• Provide a fairly strong surface when used forplastering

• Provide enough bond when used for masonry joints

Uses Of Lime Mortars

• For Foundation Works: fat lime mortar can be used inall types of foundation work in dry sub grade – watertable is 2.4 m below the foundations level.

• For All Masonry Works: loading – 20 to 60 tonnes/m2

(light and medium loading)• Fat lime and hydraulic lime, both are suitable.

• Lime mortar can be replaced by cement mortar.

• To bind stones, bricks or concrete blocks together

• Lime mortar can not be applied when:• Sub grade soil is moist – water table is within 2.4 m.

• Heavy loading is expected.

• Construction is massive and very thick.

Uses Of Lime Mortars

Hardening Of Lime Mortars

Precautions

• Mortars with hydraulic lime – should be usedwithin 4 hours after mixing.

• Lime mortars with surkhi – should be used within24 hours after mixing.

• Composite (lime and cement) mortars – should beused within 2 hours after mixing.

• All lime mortar shall be kept wet after grinding.

• The workers who are to handle lime mortarshould protect their skin by using oil rubbergloves etc.

Cement Mortars

• Cement mortar is homogeneous paste of fixed

proportion of cement, sand and water.

• Strongest type of mortar so preferred for use in

construction of structure subjected to heavy

loading

Cement Mortars

Preparation:

a. Selection Of Raw Materials: the Portlandcement must be pure, undamaged. OrdinaryPortland cement is most suitable.

• Sand: Good quality for making strong anddurable mortar – pure in composition and freefrom impurities and sharp grained in structure.

• Must be thoroughly clean before using.

• No other aggregate can replace sand completelyin cement mortars.

Cement Mortars

B. Proportioning Of The Raw Materials.

• For ordinary masonry work – 1 cement: 3 sand to1 cement: 6 sand

• For reinforced brick work & work in moistcondition - 1 cement: 2 sand to 1 cement: 3 sand

• For Architectural work – 1 cement: 3 sand

• For load bearing structures - 1 cement: 2 sand to 1cement: 3 sand

• For plaster work, it provides a water proof layerand protects the element from weathering effects

Cement Mortars

C. Mixing Of Raw Materials.

(i) Hand Mixing: For small quantity of mortar

• First clean dry sand is spread on a pucca platform and cement of required

quantity is spread over it.

• Whole mass is mixed dry by spades and required quantity of water is

added.

• This mix can be used before the initial setting time of cement

(ii) Machine Mixing: For large quantity of mortar required continuously at a

fast rate

• Cement and sand in specified proportion are put into the drum of the mixer

and required quantity of water is added.

• Drum is revolved for a sufficient period to form uniform mixture of

required consistency.

Cement Mortars

Precautions

• The setting process starts even within the first

hour of its preparation - should be used within

30 minutes after adding water to the cement and

sand mixture.

• The Structural Units – bricks and stones must

be soaked in water before laying on the wall. If

dry units, it will absorb moisture quickly.

• If Cement Sand Mortar – place should be kept

wet at least for seven days.

Uses Of Cement Mortars

• Use where high strength is required and instructures which are subjected to wet conditionsuch as piers, dams, deep foundation etc.

• Use for external plastering and pointing work

• Use for damp proof course below ground level

• Use in exposed work such as exterior walls andparapets, engineering construction with bricks ofhigh strength

• Use in concrete as cement mortar binds theparticles of coarse aggregate into one solid mass

Uses Of Cement Mortars

Gauged Mortars

• Cementing material – cement and lime both

• Lime – for economical purpose and cement – for strength.

• Methods For Making Gauged Mortars

• The three ingredients: lime, cement and sand are mixed together indry condition in predetermined volume (1 cement, 1 lime,1 sand or1 cement, 2 lime, 6 sand etc)

• Then add small quantity of water, increase the quantity of watergradually – mixing is continued till homogeneous paste of desiredconsistency is obtained.

• Lime Sand Mortar: predetermined volume of cement is added indry state then mix thoroughly. Add small quantity of additionalwater.

• Cement Sand Mortar: same as lime sand mortar but use slackedlime in finely powered form.

Plasters

• Lean mortars used mostly for covering masonrysurfaces.

• Lean mixes of cementing materials with fillers suchas sand, surkhi and crushed stones.

• Jaggery, white of eggs and soured curd are alsoadded for special effects

• Protective Plasters – saves the brick or stone fromdirect and destructive attacks of atmosphere and alsofrom wind, rain and harmful industrial gases, used onthe exterior walls

• Decorative Plasters – appealing shades and finishdesigns to the construction, used on the interior walls

Plasters

Objects of Plastering

• To provide a true, even, smooth and finished

surface to the work and improve the

appearance.

• To protect the surface from atmospheric

influences

• To cover defective workmanship

• To provide a covering for the unsound and

porous materials

Types Of Plasters

• Lime plaster, cement plaster, gypsum plaster etc.

• Lime Plasters: mixing thoroughly slaked lime andsand in ratio of 1 lime and 2-3 sand surkhi by volumewith good quantity of water till homogeneous leanpaste is obtained.

• Specially useful as protective plasters on the inner sideof the walls.

• Moghul plaster – 1 lime : 3 sand : 1 surkhi to whichsome Jaggery, white of eggs have been also mixed.

• These later materials improve the adhesive property,strength and beauty of plaster.

• Lime should be thoroughly slaked and free fromunburnt lime, grit and pebbles.

Lime Plasters

Types Of Plasters

• Cement Plaster: lean mix of Portland cement

and sand with water.

• Suitable for all type of plastering works.

• Proportion for all purpose – 1 cement : 3 sand

• Apply in single coat.

• The surface of the plaster is kept wet for at

least 3 days after application by sprinkling

water on it at regular intervals.

Cement Plaster

Types Of Plasters

• Common ratio are:

• 1 cement: 1 lime: 6 sand for external plasters, below damp proof course

• 1 cement: 2 lime: 9 sand for external plasters on walls

• Guniting Plaster: 1 cement: 3 sand which is applied under great pressure –2.5 kg/cm2 with the use of special gun.

• From gun, thoroughly mixed plaster is thrown out on the surface ofapplication with the help of compressed air.

• Gypsum Plaster: binding material – gypsum.

• Used for making architectural fancies and decorative designs on walls androofs.

• Properties Of Gypsum Plaster:

(i) Great resistance to fire

(ii) Set and harden quickly

(iii) Undergo very little expansion or contraction

Guniting Plaster

Gypsum Plaster

Sand

• Rock particles that ranges in grain size

between 2 mm and 1/16 mm.

• In composition, an oxide of silica (SiO2) .

• Mostly broken grains of mineral quartz (SiO2)

produced as result of breakdown of granites,

sandstone and similar rocks by natural process

of weathering and erosion.

Sand

Sand

Classification:

• According to mode of origin: Pit sand, stream sand andmarine sand.

• Pit Sand: generally sharp and angular – deposited by windand form accumulations in soil.

• Sand when cleaned and washed makes good mortar.

• River Sand: occur as accumulations of great extent alongthe base and banks of rivers

• shape – almost round.

• Generally free from clay, salt and organic impurities.

• Most commonly used for making mortars, plasters andconcrete.

Classification of Sand

Sand

• Marine Sand: occur on beaches and along sea shore.

• Shape – rounded grains of quartz

• Covered with the salts which are not easily separable.

• If used in mortar, concrete – salts react with the bindingmaterial.

• Marine sands are considered of inferior quality andshould be better avoided.

• If it is only source available – must be used afterthoroughly washed.

• According to composition: clean sand, silty sand andclayey sand.

Marine Sand

Sand

• Clean Sand: well graded-mostly quartz particles in widerange of grain size.

• Clean sand must be used for making mortar plaster andconcrete.

• Silty Sand: poorly graded – considerable proportion of silt(1/16 to 1/256 mm size) and other non-plastic fines.

• Clayey Sand: poorly graded – prominent clay fraction(below 1/256 mm size) and also plastic fines.

• Sand is also obtained artificially by crushing naturalquartzite rock to the required grain size.

• According to grain size: course sand – 2-1 mm, mediumsand – 1-0.25 mm and fine sand – 0.25 – 0.15 mm.

Sand

Bulking Of Sand

• Volume of sand will be more when water is present in it even insmall quantities.

• Volume of moist sand is more than dry sand.

• Bulking of sand: the change or increase in volume of sands ongetting moist.

• Important in construction.

• All the mix design denotes the proportion of sand in essentially drystate.

• Factors affecting on rate of bulking:

• Percentage of moisture content – bulking effect is maximum whenmoisture content in sand is between 4 to 6 %. As water-contentpercentage increasing – this effect goes on decreasing.

• Grain size of sand particles – fine sand shows higher bulking rateas compared to coarse sand.

Bulking Of Sand

Bulking Of Sand

References

• Building Construction : Dr B.C. Punmia

• Civil Engineering Material : Prof. Singh

• Internet Web Sites

Thanks…