plastering and painting
Short Description
Description of plastering and painting in building construction...
Description
Building Materials and Construction 6. PLASTERING, PLAST ERING, WHITE WASHING WASHING AND PAINTING Plastering Applying mortar coats on the surfaces of walls, columns, ceiling etc. to get smooth finish is termed as plastering. Mortar used for plastering may be lime mortar, cement mortar or limecement mortar. Lime mortar used shall have fat lime to sand ratio of 1: 3 or 1: . !f hydraulic lime is used mi" proportion #lime: sand$ is 1: %. &ement mortar of 1: or 1: ' mi" is very commonly used for plastering, richer mi" being used for outer walls. (o combine the cost effectiveness of lime mortar and good )uality of cement mortar many use lime-cement mortar of proportion #cement: lime: sand$ of 1: 1: ' or 1: 1: * or 1: %: *. +lastering is done to achieve the following obects 1. (o prot protec ectt the the e"ter e"ternal nal sur surfa faces ces agai agains nstt penet penetra rati tion on of rai rain n water water and and other other atm atmos osph pher eric ic agencies %. (o give give smoo smooth th surf surfac acee in in whi which ch dust dust and and dir dirtt can canno nott lod lodge ge 3. (o give decorative effect . (o pro protect sur surfface aces aga against vermin. . (o con conce ceal al infe inferi rior or mate materi rial alss or or def defec ecti tive ve wor worm man ansh ship ip /e)uirements of good plaster: 1. !t sho shoul uld d adher adheree to the the bac bacgr grou ound nd and and shoul should d remai remain n adher adhered ed duri during ng all all vari variat atio ions ns of the the climatic changes. %. !t should be be cheap an and economical 3. !t should be be hard and durable. . !t sho shoul uld d be pos possi sibl blee to appl apply y it it duri during ng all all weat weathe herr cond condit itio ions ns . !t shou should ld be be effe effect ctiv ively ely chec chec the the ent entry ry or or pene penetr trat atio ion n of moi moist stur uree from from the the sur surfa face ce '. !t shou hould pos possess good worability Materials used for lastering Li!e laster" Lime plaster is a mi"ture of calcium hydro"ide and sand #or other inert fillers$ in 1:1 ratio. &arbon dio"ide in the atmosphere causes the plaster to set by transforming the calcium hydro"ide into calcium carbonate #limestone$. !n order to improve building properties of lime plaster, gugal #a ind of fragrant gum$ 0 1.' gm3 of mortar, is added when the mortar is being ground. !n order to improve adhesive and tensile properties of lime mortar, sometimes, small )uantities )uantities of chopped hemp #i.e., vegetable fibres$ fibres$ 0 1gm3 are added to the lime mortar. (he lime mortar thus prepared is usually ept for % da ys before use. #e!ent laster" &ement and sand in re)uired proportions #1:3 or 1:$ are first thoroughly mi"ed in dry conditions and then water is added to form a paste of re)uired consistency. 2enerally, it is mi"ture of sand, +ortland cement and water mi"ed in a suitable proportions. (his prepared mortar for plastering should be consumed within 3 minutes after the addition of water. Compiled by Dr. Prashanth J. and Dr. Harish N.
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Building Materials and Construction G$su! laster %laster of Paris&" 2ypsum plaster, or plaster of +aris, is produced by heating gypsum to about 1&. 4hen the dry plaster powder is mi"ed with water, it re-forms into gypsum. (he setting of unmodified plaster starts about 1 minutes after mi"ing and is complete in about minutes but not fully set for 5% hours. Water roof laster of !ortar" (his mortar consists of 1 part of cement, % parts of sand and pulverised alum 0 1%gm3 of sand. (o this dry mi", the soap water containing about 5g of soft soaplt of water, is added to obtain the waterproof mortar. Heat resistant laster" !ts purpose is to replace conventional gypsum plasters in cases where the temperature can get too high for gypsum plaster to stay on the wall. 6eat resistant plaster should be used in cases where the wall is liely to e"ceed temperatures of &. 6eat resistant plaster is a building material used for coating walls and chimney breasts. Pro'edure for #e!ent Plastering on Wall Surfa'e &ement plastering is commonly used as ideal coating for e"ternal and internal surface of wall. &ement plaster is usually applied in a single coat or double coat. 7ouble coat plaster is applied where thicness of plaster is re)uired to be more than 1 mm or when it is re)uired to get a very fine finish. (he process of applying a double coat cement plaster on wall surface consists of the following steps.
8tep-1-+reparation of surface for plastering 8tep-%-2round wor for plaster 8tep-3-Applying first coat #or under coat or rendering coat$ 8tep--Applying second coat #or finishing coat or fine co at$ STEP()" Prearation of Surfa'e for Plastering •
9eep all the mortar oints of wall rough, so as to give a good bonding to hold plaster. &lean all the oints and surfaces of the wall with a wire brush, there should be no oil or
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grease etc. left on wall surface. !f the surface is smooth or the wall to be plastered is old one, then rae out the mortar oint to
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a depth of at least 1% mm to give a better bonding to the plaster. !f the proection on the wall surface is more than 1% mm, then noc it off, so as to obtain a
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uniform surface of wall. (his will reduce the consumption of plaster. !f there e"ist any cavities or holes on the surface, then fill it in advance with appropriate
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material. /oughen the entire wall to be plastered.
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Compiled by Dr. Prashanth J. and Dr. Harish N.
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Building Materials and Construction •
4ash the mortar oints and entire wall to be plastered, and eep it wet for at least ' hours before applying cement plaster.
STEP(*" Ground Wor+ for Plaster •
!n order to get uniform thicness of plastering throughout the wall surface, first fi" dots on
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the wall. A dot means patch of plaster of sie 1 mm ; 1 mm and having thicness of about 1 mm. 7ots are fi"ed on the wall first horiontally and then vertically at a distance of about % meters
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covering the entire wall surface. &hec the verticality of dots, one over the other, by means of plumb-bob. After fi"ing dots, the vertical strips of plaster, nown as screeds, are formed in between the dots. (hese screeds serve as the gauges for maintaining even thicness of plastering being applied.
Dots and S'reeds STEP(" Al$ing -irst #oat or nder #oat or Rendering #oat •
!n case of bric masonry the thicness of first coat plaster is in general 1% mm and in case of
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concrete masonry this thicness varies from < to 1 mm. (he ratio of cement and sand for first coat plaster varies from 1:3 to 1:'. Apply the first coat of plaster between the spaces formed by the screeds on the wall surface.
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(his is done by means of trowel. Level the surface by means of flat wooden floats and wooden straight edges. After leveling, left the first coat to set but not to dry and then roughen it with a scratching tool to form a ey to the second coat of plaster.
STEP(/" Al$ing Se'ond #oat or -inis0ing #oat or -ine #oat •
(he thicness of second coat or finishing coat may vary between % to 3 mm.
Compiled by Dr. Prashanth J. and Dr. Harish N.
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Building Materials and Construction
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(he ratio of cement and sand for second coat plaster varies from 1: to 1:'. =efore applying the second coat, damp the first coat evenly. Apply the finishing coat with wooden floats to a true even surface and using a steel trowel,
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give it a finishing touch. As far as possible, the finishing coat should be applied starting from top towards bottom and
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completed in one operation to eliminate oining mars. Defe'ts in Plaster (he following defects may arise in plaster wor. 1. 1listering of lastered surfa'e" (his is the formation of small patches of plaster swelling out beyond the plastered surface, arising out of late slaing of lime particles in the plaster. %. #ra'+ing" &racing consists of formation of cracs or fissures in the plaster wor resulting from the following reasons. a. !mperfect preparation of bacground b. 8tructural defects in building c. 7iscontinuity of surface d. Movements in the bacground due to its thermal e"pansion or rapid drying e. Movements in the plaster surface itself, either due to e"pansion or shrinage. f. >"cessive shrinage due to application of thic coat g. ?aulty wormanship. 3. Efflores'ene" !t is the whitish crystalline substance which appears on the surface due to presence of salts in plaster maing materials as well as building materials lie brics, sand, cement etc and even water. (his gives a very bad appearance. !t affects the adhesion of paint with wall surface. >fflorescence can be removed to some e"tent by dry bushing and washing the surface repeatedly. . -la+ing" !t is the formation of very loose mass of plastered surface, due to poor bond between successive coats. . Peeling" !t is the complete dislocation of some portion of plastered surface, resulting in the formation of a patch. (his also results from imperfect bond. '. Poing" !t is the formation of conical hole in the plastered surface due to presence of some particles which e"pand on setting 5. Rust Stains" (hese are sometimes formed when plaster is applied on metal laths *. ne2en surfa'e" (his is obtained purely due to poor worman ship.
Pointing (he art of finishing the mortar oints in e"posed bric or stone masonry with suitable cement or lime mortar, in order to protect the oints from weather effects and also to improve the appearance of building structure. @ften an entire wall or even a whole structure is pointed because defective points cannot easily be detected, and adacent oints may also be in need of Compiled by Dr. Prashanth J. and Dr. Harish N.
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Building Materials and Construction repair. (he mortar is paced tightly in thin layers and tooled to a smooth, concave, finished surface. S'oe of ointing
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Maintaining the oints of the structures. +ointing being cheap can be adopted in places of low rainfall. 4here the natural beauty if materials vi., stone blocs, brics etc., is desired to be
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e"hibited. 2ives resisting power to the brics and stones used in construction towards weather
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conditions. Met0od of ointing •
All the mortar oints #on the masonry face re)uired to be pointed$ are raed out by a
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special pointing tool to a depth of 1 to % mm, so as to provide an ade)uate ey for the fresh mortar used for pointing. All the loose mortar and dust are removed by brushes. (he oints and wall surface are washed with clean water, and then ept wet for few hours. (he oints so prepared, are filled with suitable mortar with a small trowel. (he mortar is
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well pressed into the oints to form a close contact with the old interior mortar oints. All e"cess mortar sticing to the sides is scraped away. (he finished pointing wor is ept wet for about 3 days when lime mortar is used for
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pointing and for 1 days when cement mortar is used for pointing.
W0ite 3as0ing 4hitewash for walls can be lime or paint-based, and can be applied to bric, concrete and other wall surfaces. +igment can be changed by adding colors to the mi"ture. >ach change in the mi"ture should be tested, however, before applied to a whole wall. +igments change when they become completely dry if you do not test the area first you may have une"pected and undesirable results. &leaning the walls first will help to ensure an even finish. More than one type of cleaner may be re)uired if you have to remove grease as well as dirt. !t is very important to clean well or it will have splotchy areas where there is dirt. !f cleaning concrete walls, use a wire cleaning brush for really tough areas but do not chip away the concrete. (horoughly apply whitewash with a paint brush. (he whitewash will apply better to a moist surface, so wet the walls first and allow it to dry partially before you start. More than one application of whitewash is usually needed. Apply thin even stroes until the wall is covered evenly. =y the time that the third coat is begun the brush stroes should no longer be visible. @ne tip to remember is that each coat needs to dry thoroughly before starting the ne"t one. 7rying time will vary based on how humid the area is. Compiled by Dr. Prashanth J. and Dr. Harish N.
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Building Materials and Construction
W0ite3as0ed 3all surfa'e
Painting +aints are coatings of fluid materials which are applied as a final finish to all surfaces such as walls, ceilings, wood wor, metal wor etc. (he process of application of paint as a coating material is called painting. (he ingredients of paints and their functions are discussed below. Ingredients of aint 1ase" !t is the main ingredient of paint. !t hides the surface to be painted and imparts durability to the painted surface. &ommonly used bases are white and red lead, inc and iron o"ides. #arrier" (he carrier is a li)uid which acts as a binder and helps to spread the ingredients uniformly on the painted surface. Linseed, (ung, +oppy, 8unflower oil etc. are some of the commonly used carriers. Drier" 7riers are metallic compounds used in small )uantities for accelerating the process of drying of paint film. Litharage, Lead acetate, Manganese dio"ide and &obalt are the driers commonly used. Sol2ent" 8olvent or thinner is a li)uid which thins the paint film so that it can be easily applied on the surface and it helps the paint in penetrating through porous surfaces. (urpentine, petroleum, spirit and highly solvent naptha are commonly used as solvent. #olouring ig!ents" (o obtain desired colour and shades of the paint, colouring pigments are added. #0ara'teristi's of aint i. !t should dry )uicly. ii. !t should be easy to apply and cover large surface area. iii. !t should not be harmful to health. iv. !t should not react with the wall or wooden material. v. (he paint should not be affected by weathering actions of the atmosphere. vi. (he paint should form a hard and durable surface. Compiled by Dr. Prashanth J. and Dr. Harish N.
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Building Materials and Construction vii.
(he paint should be fairly cheap and economical.
ses of aint i. +rotects the surfaces from the weathering effects of the atmosphere and actions by other li)uid, fumes and gases. ii. +revent the decay of wooden members. iii. +revent the corrosion of metallic surface. iv. +rovide a smooth surface for easy cleaning. v. +rovide pleasing, colourful and decorative appearances to the surfaces. vi. !ncrease the life of the buildings. vii. !t covers the defective wormanship and materials. T$es of aints 1. 4il aint" (his is an ordinary paint. !t is generally applied in three coats namely priming coat, undercoats and finishing coats. !t is ver y cheap and possesses opacity and low gloss. %. Ena!el aint" (his paint consists of white lead or inc white ground in a small )uantity of oil and mi"ed with petroleum spirit and resinous matter. !t is available in different colours. 3. E!ulsion aint" !t consists of polyvinyl acetate and synthetic resin as binding materials. !t is easy to apply and dries )uicly. &olour of paint is retained for a long period. !t can be cleaned by washing with water. . Alu!inu! aint" (his consists of aluminum powder suspended in spirit varnish or oil varnish. After the application of the paint the spirit becomes evaporated and the aluminum is deposited on the surface as thin layer. Aluminum paint has the advantage such as visibility in darness, imperviousness to moisture, good appearance to the surface, high electrical resistance and resistance to heat and sunlight. . 1itu!inous aint" !t is prepared by dissolving asphalt or vegetable pigment in any type of oil or petroleum. !t presents a blac appearance. (his type of paint is used to paint iron grills. '. #e!ent aint" (his type of paint is prepared by using white cement, pigment accelerators and other additives. !t is available in various colour and available in dry form. !t is water-dilutable paint. !t is mainly applied on bric and cement surface and resists the penetration of moisture. !t gives long life. 5. Plasti' aint" (he paint contains necessary variety of plastics. !t is available in the maret under different trades and colours. (he plastic paint can be applied either by brush or by spray painting. !t gives recreation, pleasing and good appearance. Met0od of ainting old 3ood 3or+ +reparation of surface for painting old wood wor: i. (he surface of the old wood wor should be cleaned by using sand paper.
Compiled by Dr. Prashanth J. and Dr. Harish N.
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Building Materials and Construction ii.
@ld surface should be cleaned by using a litre of water mi"ed with % gm of caustic soda and lime to remove the old colours. iii. Bails if any should be removed. +rocedure of painting old wood surface: i. +riming coat is applied on the surface to reduce )uantity of oil paint. ii. After drying of the priming coat the first coat of paint is applied on the surface. iii. After drying of the first coat of paint second and third coats will be applied on the surface subse)uently. Met0od of ainting ne3 3ood 3or+ 1. +reparation of surface for painting: (he surface to be painted should be carefully cleaned and rendered smooth. %. 9notting: 9notting is of three types. (he commonly adopted two types are, i. @rdinary notting: (his is applied in two coats. (he first coat consists of hot lead ground in water with strong glue added to it. After drying, the second coat is, applied which consists of red lead ground in oil and thinned with turpentine. =y doing this nots are removed. ii. +atent notting: (his consists of two coats of varnish which is made by dissolving shellac in methylated spirit. 9nots are removed by applying this mi"ture. =oiled lime is also used to remove nots. 3. +riming coat or first coat: After notting the priming or first coat is applied to the whole surface of the wooden article to be painted. . 8topping: After priming the process of stopping is carried out. After stopping dries, the surface is well rubbed down with emery sheets and cracs if any filled with putty. (his is nown as stopping. . Application of succeeding coat: +ainting is done by good )uality brush. ?inally, two coats of paint are applied one after the other. (he second coat is applied only after the first coat is dried thoroughly. 4hile painting, the brush is held at right angles to the surface and only the hairs should touch the surface. !f necessary after drying of second coat the third coat is also applied.
Defe'ts in 3ood
Compiled by Dr. Prashanth J. and Dr. Harish N.
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Building Materials and Construction Met0od of ainting old iron and steel 3or+s +reparation of the surface: i. (he iron and steel wor to be painted is made free from all mill scale, loose rust and grease by using iron brushes. ii. (he old paint on the iron wor should be cleaned by using phosphoric acid. +rocedure of painting: i. (he surface to be painted is cleaned with emery sheet. ii. 6oles if any on the surface should be filled with metallic paste. (hen as the priming coat, red o"ide is applied on the surface. (his is cheap. +ainting adheres well on it. Met0od of ainting ne3 iron and steel 3or+s +reparation of surface: (he iron or steel wor to be painted is made free of all mill scale, loose rust and grease by using iron brushes. (he loosened scales are removed by a et of hot water, followed by a bath of hydrated lime and petroleum. &leaned metal surface is finally treated with phosphoric acid.
Application of coats of paint: 8urface of steel wor is cleaned and dried. After this a priming coat is applied. After this has dried the second coat of paint is applied by using brush or spray. (he completed paint surface should be smooth and uniform. Met0od of 'e!ent ainting on 3all surfa'e +reparation of surface: i. Bewly constructed wall surface is wet. (he wall surface should not be painted until it is completely dry. (ime duration of drying depends on the ventilation and weather condition. +ainting on a freshly plastered surface should be avoided for atleast 3 to ' months. ii. (he wall surface should be prepared well before painting to remove free lime or cement in the wall. @therwise, it will discolour the pa int and destroy its oil. (o avoid this priming coat is applied which does not consist of chemicals that reacts with alaline. iii. +ainting should be done only after the surface is given a cost of siing #glue mi"ed with water$ to fill up the cracs. iv. 4hite patches that occur on the plastered surface can be removed by water washing with wire brush. !f white patches appear again painting should be delayed. v. 4hile painting, if any change occurs antiseptic washing treatment is given.
Application of cement paint: i. !nitial coat of white cement is applied on the e"terior walls. ii. After curing is completed first coat primer is applied. iii. Above the primer coat, two coats of cement paint are applied. 6ence, incomplete portions are finished by the second coat. Compiled by Dr. Prashanth J. and Dr. Harish N.
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Building Materials and Construction iv.
?inishing coat is applied in the opposite direction of the previous coat.
I!ortant oints to 5e 'onsidered 30ile ainting i. =rush: =rush used for painting should be of fibre bristles and not by using horse hairs. @nly then more )uantity of paint could be taen by the brush which will facilitate for easier painting. (he brush should be cleaned by erosene after the application of the paint. ii. +aints: /eady mi"ed paints available in the maret can be used. 8ince it is highly e"pensive two or more colours of paint are ept in stoc and the re)uired colour may be changed according to the situation. ?or this, paint is taen in a solid state in a container and it is stirred well by adding linseed oil. (hen by adding pigments for a re)uired colour and suitable ingredients the paint is prepared. iii. 9notting: =efore painting the wooden surface the process of removing not on the surface by hiding it and painting over it is called notting. +aint should be applied only after notting. iv. +riming coat: A coat of cheap rate paint is applied. v. 8topping: After completing the first coat it should be rubbed by emery sheet and pumice stone. (hen stopping is carried out and second coat is applied. vi. &oating: generally painting should be applied in % or 3 coats. Application of first coat is called primary coat. 8econd coat is called base coat. (hird coat is called final coat. vii. 8pray painting: !nstead of painting with ordinary brush the surface can also be painted with spray pistol by passing the air with pressure. (his is called as Cspray paintingD. 8pray painting is better than painting with brush. !t includes special features lie speed, )uality, economy and labour. Defe'ts in ainting, 'auses and re'autions Sl. Defe'ts #auses
Pre'autions
No.
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%
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=listering
!t is caused due to the Avoiding drops of water, water trapping of water vapor vapor on the painted surface behind the painted surface =looming: ?ormation 7ue to bad ventilation and Allowing ventilation and using of dull patches on the defective paint good )uality paint finished surface ?ading: 2radual loss 7ue to the direct sunlight Avoiding direct sunlight and of colour effect painting colours of light shades ?laing: Losing small !t is caused when the adhesion +ainting on the surface which is portion of the paint is poor having sufficient adhesiveness surface and allowing it to dry. ?lashing: 2lossy +oor wormanship and poor 2ood )uality of paint is applied patches on the )uality paint with an efficient painter
Compiled by Dr. Prashanth J. and Dr. Harish N.
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Building Materials and Construction painted surface '
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2rinning: &lear ?inal coat of the paint does visibility of the not have sufficient opacity bacground /unning: +aints run 4hen the surface to be bac and leaves small painted is smooth areas of surface uncovered 4rinling (he horiontal surface is too thicly painted
?inal coat should be given with utmost care. (he surface to be painted should be rubbed with emery paper and painting is carried out (hin coat of paint is applied on the horiontal surface
Defe'ts in Painting
arnis0es Earnish is a solution of resins or resinous substances lie shellac, cobalt in oil, turpentine or alcohol. Ne'essit$ i. (o provide a brilliant and decorative covering on wooden surface. ii. (o protect the painted surface form the atmospheric action. iii. (o protect unpainted wooden surface of doors, windows, floors, roof trusses etc., from atmospheric action.
Compiled by Dr. Prashanth J. and Dr. Harish N.
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Building Materials and Construction
arnis0 5eing alied on 3ood surfa'e
arnis0ed 3ood surfa'e
Diste!ers (hese are paints used for the treatment of masonry walls. !n distempers water is used instead of oil as carrier. (hese are also nown as water paints. !t is made by mi"ing whiting and glue boiled in water. (hese are mi"ed with water at the time of use and applied on the plastered surfaces. (hey give better finish and are long lasting. (hey are suitable for high-class interior decorative finishing wor on the walls and ceilings. As distempers are affected by weather and peels off, if washed, so its use is restricted only to interior wors.
Compiled by Dr. Prashanth J. and Dr. Harish N.
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