17 Painting Anjana
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Transcript of 17 Painting Anjana
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PAINTING
ANJANA GOWRI
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PAINTING AND PAINTS
Painting
Practice ofapplyingpaintto a surface (knownas base
material).
To impart decorativeand protective finish.
The base materialcan beconcrete, wood, metal,
masonry orplaster surfaces.
Paints
Liquid compositions ofpigments and binders Thincoats applied dryto form a solid film
Film imparts smooth, decorativeand protective finish
to that surface.
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PURPOSE OF PAINTING
Protection: Paint serves as aprotective shield betweenthe base materials
and the deterioratingelements
Theelements can be sunlight,temperaturevariations, fresh andsalt water, watervapour,rot, mildew,chemicals,and abrasion.
Preservetimberelements against warpingand decay. Preventcorrosion of metals.
Illumination: Lightcolours reflectlightand help brightentheroom.
Gloss paints reflect morelightand createglare hence should beavoided.
Improvegeneralappearance ofthe structure. Sanitation And Cleanliness:
Paintcoatingprovide smooth,non-absorptive surfaces whichareeasily washed and kept free of dirt.
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CHARACTERISTICS OF AN IDEAL
PAINT
It should form hard and durable surface.
It should giveattractiveappearance.
It should becheapand readilyavailable.
It should beeasilyapplicable. It should havegood spreadingquality (max.areain
min.quantity)
It should dryinreasonabletime.
It should not show haircracks on drying. It should form film of uniform colour on drying.
It should be stable foralongerperiod.
It should not beaffected byatmosphericagencies.
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CONSTITUENTS OF PAINT
Apaintgenerally has the following
constituents:Base
Vehicle orcarrier
Drier
ColouringPigment
Solvent orthinner
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BASE
Solid substancein finepowder form.
Forms bulk ofthepaint.
Generallya metallic oxide.
It determines thecharacter ofpaintand imparts
durabilityto the base material. Provides opaquecoatingto hidethe base material.
Commonly used bases are: Whitelead
Red lead
Oxide of zinc (zinc white)
Oxide ofiron
Titanium white
Antimony white
Aluminium powder
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VEHICLE ORCARRIER ORBINDER
Liquid substance holdingthevarious constituents in
liquid suspension.
Helps in spreadingthepaintevenly ona surface.
Generallypreferred vehicles are: Various forms oflinseed oils :
Drylinseed oil thinner forinterior work.
Double boiled linseed oil dries quickly forexternal
work
Tug oil for superiorqualitypaints
Poppy oil forlastingcolours
Nut oil
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DRIER
Used to acceleratetheprocess of dryingand hardening.
Works byextracting oxygen from theatmosphereandtransferringitto thevehicle.
Not used in finalcoatas theyreducetheelasticity ofpaint
Two types: Liquid driers: Finelyground compounds ofcobalt,lead and
manganese dissolved inavolatileliquid
Paste driers: Cobalt,lead and manganese mixed with largepercentage ofinert fillers like barytes and ground inlinseed oil.
Advantages ofinert fillers are: Reducecost ofpaint
Improve durability
Modifythe weight
Prevent shrinkageand cracking
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o Theyarealso knownas adulterants and hence shouldnot be used inexcess.
o Weight should notexceed one-fourth the weight ofthe
base.
o Generally used driers are:
Litharge (PbO) Red Lead (Pb3O4)
Sulphates of zinc
Sulphates of manganese
o Lithargeis mostcommonly used.
o Lead driers avoided with zincpaints.
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COLOURING PIGMENT
Added to baseto give differentcolours.
The desired shadeis obtained bythe use of single or
combination ofthepigments.
Majortypes based ontheir originare: Natural Colours : Ochres,Umbers and iron oxides
Calcined Colours : Lamp black, Indianred,carbon black,
Red lead
Precipitates :Prussian blue,chromegreen,chrome
yellow
Lakes :Prepared by discolouring barytes or
chinaclay with the help of suitable dyes
Metalpowders :Powders ofaluminium, bronze,copper,
zinc,etc
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TINT AND THE PIGMENT USED
Black
Blue
Brown
Green
Red
Yellow
Lamp black,carbon black, bone black,
graphite
Indigo,Prussian blue,cobalt blue,
ultramarine
Burnt umber,raw umber, burnt sienna,Vandyke brown
Paris green, Chromegreen, Greenearth,
virdigris copper sulphate
Indianred,veniteanred,vermillionred,
carmine,red lead
Chromeyellow,raw sienna,yellow occhre,
zincchrome
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SOLVENTS OR THINNERS
Added to makethepaintthin so thatitcan beappliedeasily.
Helps thepaintinpenetratingtheporous surface ofthe
background.
Reduces thegloss ofpaint.
Mostcommonly used thinneris turpentine oil.
Forexternal use minimum quantity ofturpentineis used
as itis affected by weather.
Few paints and thethinners used inthem are:
Oilpaints Spirit ofturpentine, Naphthaand Benzine
Cellulosepaints Ethylamylacetate
Distempers Water
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CLASSIFIACTION AND TYPES
OF PAINTS
Three majorclassifications:
Based on binders
Based onthe ultimate use
Mixed classification
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MIXED CLASSIFICATION
Aluminium Paint Finelyground aluminium suspended inquick drying spirit
varnish or slow-drying oilvarnish
Athin metallic film ofaluminium is formed whenthe spiritor oilevaporates.
For wood work or metal surface
Advantages: Weatherresistant
Waterproof
Highly heatreflective
Corrosionresistant
High electricalresistance
High coveringcapacity Visibilityin darkness
Betterappearance
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Anti-corrosivePaint Protect metal surface from corrosion
Oil (mostlylinseed oil), strong drierand colouring mixed withfine sand.
Cheaperthan white/lead paints.
Lasts longer
Disadvantage: Gives a black appearance
Asbestos Paint Contains fibrous asbestos
For surfaces exposed to acidicgases and steams and also forpatch work or stoppingleakagein metalroofs.
Paintinggutters, flashings etcto preventrusting.
Bituminous Paint
Prepared by dissolvingasphalt ortarinnaphtha or whitespirit.
Alkaliresistant
Gives black colourand deteriorates whenexposed to sunlight.
Used for under water steeland iron mains
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BronzePaint
Vehicle :nitro-celluloselaquer
Pigment:aluminium bronze orcopper bronze
High reflectiveproperty
Forinteriorand exterior metallic surfaceand onradiators
CaseinPaint
Casein (proteinextracted from milk) mixed with base having
whitepigments
Applied on walls,ceilings wall boards etc.
Tinted inany desired shade
Littlequantity ofvarnish added while usingexteriorly.
CellulosePaint
Prepared from nitrogen-cotton,celluloid sheets,photographic filmand amylacetate substitutes.
Paint hardens byevaporation of solvent
Gives very smooth finish
Very high cost
Used forpainting motorcars and aero planes
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EnamelPaints Contains metallic oxide(whitelead or zinc white), oil,petroleum
spiritand resinous material.
Dries slowly Produces hard,impervious,glossy,elastic smooth and durable
film.
Painted surface unaffected byacid,alkali, orany fumes
Commonly used on doors, windows, metalgrills etc.
GraphitePaints Black colour
Foriron surfaces incontact with ammoniachloride, sulphurgases etc.
Used for mines and underground surfaces.
Inodorous Paints
Has whitelead or zinc white mixed with methylated spirit. Shellac with traces oflinseed oiland caster oilis mixed with
spirit.
Spirit dries quicklyleaving behind thin film of shellac.
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OilPaints Mostcommonly used
Vehicle: Linseed oil, boiled linseed oil,tug oiletc.
Base: Whitelead,red lead,titanium oxideetc.
Mainly 3 coats :prime, underand finish coat
Cheap,easyto applyand has good capacityand low gloss
Used inallgeneral works like walls ,ceilings etc
Not suitable for humid and damp weather
PlasticPaints Base:Plastic
Quick drying, high coveringpowerand decorativeappearance
SilicatePaints Has calcined and finelyground silicaand resinous substance
Silicaimparts good adhesion
Becomes hard and durable on drying
Heatand alkaliresistant
Synthetic RubberPaints Has syntheticresins dissolved inappropriate solvents
Acid,alkaliand moistureresistant
Dries quickly with uniform colour
Moderatecost
Applied oncementconcrete (internaland external)
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PAINTING NEW WOOD WORK
Mainly has six major steps:
Preparation of surface
Knotting
Priming
Stopping
Under-coatings
Finishing Coat
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Preparation OfSurface
Surface dusted to remove dustand foreign matter
Heads ofnails punched to a depth 3 mm below the surface
Greasy spots removed using white muslin soaked inturpentine
Surface dried and glass papered.
Knotting
Process ofcoveringthe knots in wood work with substances
Theypreventresins from coming out
Two methods : Ordinary knottingand Patent
Ordinary knotting:
Two coats applied.
Second applied 10 mins after firstcoat.
Firstcoatis of heated solution ofred lead, waterand glue
Second coatis ofa solution ofred lead,linseed oiland turpentine
Patent:
Coat of hotlime
Scraped offafter 24 hrs.
Ordinary knottingcarried out
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Priming
Process ofapplying firstcoat ofpaint (primer)to closethepores
Surfacerubbed with abrasivepaper Proportion of ingredients inpaintvaried from consecutive
layers
Usuallyit has 3kgeach ofred lead and whitelead mixed with
3L ofturpentine
Differentcomposition forinternaland external work Applied before fixingthe wood work inposition.
Stopping
Process ofrubbing down surface bypumice stone orglass paper
Cracks and nail holes filled with putty ( chalk +linseed oil)
Afterputty dries up, surfaceagainrubbed with pumice stone For hard work hard stoppingis done one-third whitelead +
ordinaryputty
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Undercoatings
Second and third coatings applied
Firstcoatis primecoat
Same shadeas finishingcoat
Sufficienttime for dryingprovided betweenthecoats
For superior work,each coatrubbed down bypumice stone
beforenextcoat
Finishing Coat
Applied afterthe under-coatis perfectly dry
Should be smooth, uniform and free from patches and
brush marks
Applied bya skilled painter only
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RE-PAINTING OLD WOOD WORK
Oilpaintremoved by:
Applying solution ofcaustic sodaand water
Applying mixture of soft soap,potash and quick limeand
washed offafter 24hrs.
Applying mixture of washing sodaand quick limeandwashing offafteran hour.
Surfacecleaned usingpumice stone orglass paper
Two orthree fresh coats applied.
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PAINTING NEW IRON AND STEEL
WORK
Cleaning of surface:
Scaleand rustcleared by scrapping or brushing with steel
wire brushes.
Oiland grease by washing surface with petrol or benzene.
Cleaned surfacetreated with film ofphosphoricacid topreventrustingand improves adhesiveproperty.
Prime or firstcoat (red lead and linseed oil)applied using
brush.
Two or more under-coats applied aftertheprevious coatis
completely dry.
Finalcoatapplied afterthe under-coats dry.
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DEFECTS IN PAINTING
Blistering
Caused by bubbles underpaint film.
Formed dueto watervapourtrapped behind the surface.
Bloom
Formation of dullpatches Defectinpaint or bad ventilation
Crawling or sagging
Excessivethickness ofpaint
Fading
Gradualloss ofcolour Effect of sunlight onpigments
Flaking
Dislocation of smallportions ofpainted surface
Dueto pooradhesion
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Flashing
Formation ofglossypatches
Dueto bad workmanship,cheappaint or weatheraction
Grinning
Defectin which the background or surface of base material
is clearly seen.
Dueto insufficient opacity of finalcoat.
Running
Formation of smallareas notcovered bypaint.
Dueto very smooth base surface which causes thepaintto
run.
Sponification
Formation of soappatches onpainted surface
Dueto chemicalaction ofalkalies.