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PAINTS AND VARNISHES Paints and varnishes are used to protect metals, timber, or plastered PAINTS AND VARNISHES Paints and varnishes are used to protect metals, timber, or plastered

PAINTS AND VARNISHES Paints and varnishes are used to protect metals, timber, or plastered - PowerPoint Presentation

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Uploaded On 2022-08-04

PAINTS AND VARNISHES Paints and varnishes are used to protect metals, timber, or plastered - PPT Presentation

Weather Heat Moisture or Gases etc and To improve their appearance Paints in common can be classified as Oil Paints Water Paints Cement Paints and Bituminous Paints There are some ID: 935140

oil paints paint surface paints oil surface paint drying varnish varnishes spirit lead commonly water hard polish base painted

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Slide1

PAINTS AND VARNISHES

Paints and varnishes are used to protect metals, timber, or plastered surfaces from the corrosive effects of :Weather, Heat, Moisture or Gases etc. and To improve their appearance.Paints in common can be classified as: Oil PaintsWater Paints Cement Paints, and Bituminous Paints.There are some special paints used for some special purposes e.g. Heat Resisting Or Fire Proof Paints, Chlorinated Rubber Paints (For Protection Against Acid Fumes etc.), Luminous Paints (For Visibility In The Dark).

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Slide2

Composition of Oil Paints

Oil Paints consists essentially of – A base, A Vehicle (always oil) One or more coloring pigments, A solvent or thinner Drier, An inert filler.Base :- Base provides body to the paint and on it depends the nature of paints to a great extent :PropertiesIt is the solid matter forming the main body of the paint.It makes the paint film harder and more resistant to abrasion.It forms an opaque layer to obscure the surface of material to be painted.It reduces the shrinkage cracks formed on drying.White Lead, Red Lead, Zinc Oxide (or Zinc White), Iron Oxide, and metallic powders such as Aluminum, Copper and Bronze etc. are the commonly used bases.Paints are very often named after the bases used, e.g. Lead Paints, Zinc Paints, Aluminum Paints, etc.

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Slide3

Vehicle :-

It is an oily liquid in which the base and pigment are soluble.It facilitates the paint to be conveniently spread evenly over the surface by means of the brush.It acts as a binder for the base and causes it to stick to the surface. On drying it forms a tough and an elastic film.Oils most commonly used as vehicle are : Linseed oil, Poppy oil, Nut oil etcColoring Pigments:- These are finely ground coloring matter. Their main function is to give color and opacity to the paint. Pigments are liable to fade because of the bleaching action of the sun. These are also subjected to change of color under the influence of moisture, heat, or hydrogen sulphide. Commonly used pigments are:Blacks – Lamp black, vegetable black, ivory blackBlues – Indigo, Prussian blue.

Yellows

– Chrome yellow, raw

siena

, yellow ochre.Greens – Copper sulphate.Browns – Raw umber, burnt umberRed – Red lead, vermilion, carmine

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Slide4

Solvent or Thinner

:-A liquid thinner is added to the prepared paints to increase their fluidity to the desired consistency so as to make them work more smoothly and also to help penetration of porous surfaces. Oil of turpentine is the most commonly used thinner.Drier :- Driers are added to paints to quicken the drying of the vehicle. Linseed oil dries by absorbing oxygen and it could be achieved by adding substances rich in oxygen. Some of the commonly used driers are : Litharge, Red Lead, Lead Acetate, Manganese Dioxide and Zinc sulphate.Inert Filler :- It is an adulterant mixed to replace the base in part and thus reducing the cost of paint. Commonly used fillers are: silica, Charcoal, powdered chalk,

aluminum silicate, and

barium

sulphate

etc.4

Slide5

Characteristics of a Good Paint

It should have good body or spreading power.It should work smoothly and freely and be capable of being laid in a thin coat with brush.It should form durable, tough and resistant to wear, film on drying.Colour of paints should not fade or change.It should become surface dry in about 9 hours and hard enough to take another coat in 24 hrs.It should not crack on drying.It should give a smooth and pleasing appearance showing no brush marks.It should dry quickly.It should not damage the painted surface.5

Slide6

Defects in Painting 

Cracking :- Cracks extending throughout the thickness of paint are caused by improper seasoning of painted wood, excessive use of drier or application of too many coats resulting in an excessive thickness of paint. It results in scaling of paint.Crazing and Crocodiling :-Use of too much oil, use of impure oil and insufficient drying of undercoat may cause hair line cracks in top coat. If these hair line cracks encloses small areas then the defect is known as CrazingHowever if the areas enclosed are large then the defect is known as Crocodiling.Blistering and Peeling :-Exposure of paints rich in oil, to strong sunshine causes blisters. Blisters are also caused if oil or grease is left on the surface to be painted. Painting a surface with moisture present on surface or in pores of the wood causes peeling.Runs and Sage :- The causes of this type of defect are:Application of too thick or slow drying paint, Painting over a glossy surface, Use of excessive drier or excessive humidity and

Change of temperature during drying period

.

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Slide7

Chalking

:- Use of insufficient oil in priming coat causes the paint to rub off with hands or clothes. This defect is called chalking.Washing Off :-Use of pigment soluble in water causes the deposit of dissolved matter at lower edges forming streaks.Dull Appearance :- It is caused by use of excessive drier, or, the paint becoming old.Slow drying :- Use of inferior or old oils, painting over damp surfaces or during unfavourable weather condition causes this defect.7

Slide8

Enamel Paints 

Enamel consists of high grade bases like zinc oxide or lead oxide ground in oil or varnish. They dry slowly leaving a hard, tough and elastic film which is smooth and durable. Enamel painted surfaces are washable and are not affected by acids, alkalis, gases or steam.These can be made in any tint, however delicate. Even though they are more costly than ordinary paints yet, because of their durability, they ultimately prove to be more economical. Enamel paints made from synthetic resins are known as Synthetic Enamel, and are available readymade in the market.Distempers  These are the paints used for the treatment of plastered surfaces. They contain Water instead of Oil as a carrier, and therefore are sometimes also called as water paints. It is made by mixing whiting and size with water. Powdered white chalk forms the whiting and glue boiled in water forms the size. Whiting takes the place of white lead in oil paints as a base. It is usually coloured by mixing with earthy pigments such as Ochre, Umber, Indian Red and Lamp Black. All prepared distempers are mixed with water before being used.As the distemper is affected by weather and comes off on washing, its use is restricted only in the interiors of the houses. These should be applied in dry weather after the surface has been cleaned and dried.

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Slide9

Varnishes

Varnish is a solution of resin in either oil of turpentine or alcohol. It dries after applying leaving a hard, transparent and glossy film of resin over the varnished surface.Varnish is applied : To the painted surface to increase its brilliance and to protect it from the atmospheric action.To the unpainted wooden surface with a view to brighten the ornamental appearance of the grains of wood.Composition : The ingredients of varnish areResinsSolventsDriersResins : Commonly used resins are :Copal ( it is a hard, shining, generally bright yellow or brown in colour, found embedded in earth. ), Mastic,

Amber gum, and

Lac.

Copal is considered to be the best, toughest, hardest, and is very durable for external work.

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Slide10

Driers:

These should be used only in small quantities as the excess injures varnish and impairs its durability. Litharge or Lead Acetate are the commonly used driers in varnish.Solvent: These must suit the Resin used. Boiled Linseed oil, is used to dissolve copal or amber, Turpentine oil for common resins or mastic, methylated spirit for lac.Qualities of a Good VarnishIt should dry quickly.On drying it should form a hard, tough, and durable film.It should have good weathering properties, resist abrasion, and wear well.It should be able to retain its colour and shine.It should be uniform and pleasant looking on drying.

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Slide11

Different Kinds of Varnishes

: Based on the different solvents used varnishes are classified as follows Oil Varnish: These are made by dissolving hard resins like amber or copal in oil. They are slow on drying, but are hardest and most durable of all varnishes. These are suited for being used on exposed surfaces requiring polishing or frequent cleanings or for superior work.Turpentine Varnish: These are made from soft resins, like mastic common resin dissolved in turpentine oil. They are cheaper, lighter in colour and dry more quickly than oil varnish, and are less durable and are not so tough.Spirit Varnish: Varnishes in which spirit is used as a solvent are known as Spirit Varnishes or French Polish Shellac is dissolved in spirit and the product is applied in a thin layer. These varnishes give a transparent finish thus showing the grains of the timber.Water Varnish: They consist of Lac dissolved in hot water with borax, ammonia, potash, or soda just enough to dissolve

lac

.

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Slide12

French Polish or Spirit Varnish

It is prepared by dissolving pure shellac, varying from pale orange to lemon yellow in colour and free from resin or dirt, in methylated spirit at the rate of 0.15 kg of shellac per litre of spirit. It may be coloured by adding some pigments. The solution is than strained through double thickness of coarse muslin.Before applying French Polish the surface is cleaned of dust. It is then coated with a filler called Primer, as otherwise the French polish will get absorbed by the wood and good gloss will not be obtained.A pad of woolen cloth is wrapped in fine cloth and used for applying the polish. The pad is moistened with the polish and rubbed hard on the surface to be polished . The polish is used sparingly but uniformly on the surface. Rubbing is done in a series of overlapping circles. Subsequent coats are applied after the previous one has dried. The finishing coat is applied with the pad moistened with methylated spirit and rubbing the surface lightly and quickly to give the surface a uniform texture and high gloss.12