17 Painting Anjana

8/6/2019 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.

17 Painting Anjana

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