Paint and varnish . presentation
- 1. Contents PAINTS Constituents of paints Types of paints Painting techniques Manufacture of paint Painting Defects Tests for suitability of paint Application of paint VARNISH Procedure of vanishing Ingredients of Varnish Types of Varnish Manufacture of varnish Tests for suitability of Varnish
- 2. PAINTS Paints are the coatings of fluid materials which are applied as a final finish to all surfaces, such as walls, ceilings, wood work, metal work etc. The process of application of paint as a coating is termed as painting. Constituents of paints Base: a base is a solid substance of a metallic oxide in fine state of division. It is a principal constituent of paint. The base makes the paint film harder, stronger, elastic, safe against cracking and moisture Vehicle: a vehicle is a liquid substance which keeps the ingredients of paint in liquid suspension. It dries on exposure (drying oil) Drier: a drier is a substance which accelerates the process of drying of a paint film. Acts as a catalyst in the oxidisation process of the drying oils. Colouring pigment: colouring pigment gives required colour for paints.
- 3. Solvent: it is a volatile liquid which is mixed in a paint to make the paint thin so that it can be easily applied on the surface.it must exhibit capacity for taking all the other components into solution and evaporating quickly on exposure to the atmosphere. Fillers; this can be added to paint to increase the bulk volume without effecting its useful properties. Materials used for fillers are inert. PROPERTIES OF AN IDEAL PAINT 1. It should be possible to apply easily and freely. 2. It should dry in a reasonable time. 3. It should form hard and durable surface. 4. It should not be easily affected by atmosphere (chemically inert) 5. It should possess attractive and pleasing appearance.
- 4. 6. It should not be harmful to the health of workers. 7. It should have a good binding power so as to cover the surface its applied on completely and thoroughly 8. it should be economical in cost OBJECTIVES OF PAINTING • it prevents decay of wood and corrosion of metals. • It is used to give good appearance to the surface • It protects the surface from weathering effects of the atmosphere. • It provides a smooth surface for easy cleaning.
- 5. TYPES OF PAINTS DEPENDING ON THEIR CONSTITUENTS Aluminium paint: it contains finely ground aluminium in spirit or oil varnish. It is widely used for painting gas tanks, water pipes and tanks. Oil paint: this is the ordinary paint and it is generally applied in three coats of varying composition. The oil paints are used in general for all types of surfaces, such as wood work, walls, ceilings, metal work etc. They have a low order shine, they contain unsaturated oil and their hardening is because of oxidation of the oil on exposure to the atmosphere. Enamel paint: it contains white lead or zinc white, oil, petroleum spirit and resinous material. It can be used for both external and internal walls.it forms a hard, impervious enamel like surface on drying. Bituminous paint: this type of paint is manufactured by dissolving asphalt or vegetable bitumen in oil or petroleum. It is used for painting iron works under water.
- 6. Emulsion paint: it contains binding materials such as polyvinyl acetate, synthetic resins etc. It can be defined as a suspension of one liquid within another. One liquid in this case is the paint source and the other a carrier. This paint is recommended for use on stucco, bricks and masonry surfaces which contain free alkali. Distempers: Distempers are the cheaper variety of paints in which chalk is used as base and water is used as a carrier. Properties of distemper • They are generally light in colour. • They give reflective coating. • The coatings a generally thick. • They are less durable than oil paints. • They exhibit poor workability.
- 7. The various types of distempers are: White distempers: they are made by mixing only whiting i.e, powdered chalk and glue size. Coloured distempers: they are prepared by mixing the desired colouring pigment to the whiting before mixing it with glue size. Oil bound distempers: there is a variety of oil paints in which the drying oil is treated that it mixes with water. Such distempers are diluted or thinned with water when required. Casein paints: these paints are prepared by mixing a finely ground casein with a white base usually slaked lime. Cold water paint: These constitute of mineral pigments carried in driers and binders like soya bean, casein. These paints are easily washed away by water and as a result, they are used for interior works.
- 8. Lacquers: This is a suspension of resins and cellulose ester in a volatile state. Lacquers are made from cellulose ester like cellulose nitrate and cellulose acetates which form a film, plasticizers these improve properties of the paint such as toughness, resistance to deterioration to weather and the adherence of paint for example castor oil, they also include diluent and desired pigments and resins which improve the adhesion onto the surface. Synthetic resins paint: Synthetic resins differ from the natural paint resin and classified as esterification or organic compounds for example epoxy resins, polyurethane resins and acetal resin. Synthetic paints are paints that have the resin components as one of the above resins. These set quickly and more durable when used in corrosion areas compared to other paints
- 9. Asbestos paint: These are paints that have fibrous asbestos and are used in repairing leakages in roofs and for painting gutters Bituminous paints: These are paints made from asphalt bitumen. They are black in colour and they reduce moisture permeability. They are used for exterior works and plastered surfaces.
- 10. Techniques used for painting By brushing In this method of application of paint, brushes and rollers are used to apply paint onto the surfaced to be painted. In this method, buckets are used to carry the paint during the painting. The brushes used range in size from 1 to 4 inches that is about 25mm to 100mm respectively. While painting with this method, one should start from the top most part of the surface and paint downward in order to avoid the running defect. The brush is dipped in the paint and the excess removed by drawing it against the edge of the tin. You paint with a narrow strip and use vertical brush strokes. The area is then painted with horizontal brush strokes. If another coat is to be applied, the surface is first let to dry and then the next coat applied.
- 11. By Spraying This is mainly used for cellulose paints. It is done in two ways either by using a hand spray gun or by using an air compressor when spraying on large scale. The spray gun consists of a spray gun that has a nozzle and a trigger, a motor and fan giving a current of air delivered by tube to a container Spraying, on a large scale is better than brushing and it also uses less paint.
- 13. MANUFACTURE OF PAINT Making the paste: the pigment in powder form is mixed with the resin to from a paste Solvents and the required additives are added to the paint. Additives are components added to improve the properties of the paint such as surface tension, its flow, the finished appearance and many others. Dispersing the pigment: This is a process of evenly distributing the pigment throughout the solution. The paste mixture is routed in a sand mill in order to stir up tiny sand particles or silica which grind the pigment particles and disperse them throughout the mixture.
- 14. The mixture is then filtered in order to remove the sand particles or silica. Or the paste mixture can be processed using a high speed dispersion tank Here the premix is subjected to high speed agitation by a rotating shaft that has circular toothed blades This blends the pigment into the solvent Thinning the paste: The paste is now stirred up with the appropriate solvent in order to produce a desired paint type. Canning: The now ready paint is packed in suitable containers the most common being the 8 pint paint cans, 20 liter jerry cans and buckets.
- 15. Methods of manufacture of paint High Speed Mixers High Speed Mixers consist of a tank in which the paste is placed, a motor and a shaft with circular toothed blades. The dispersion of the pigment is obtained by the violent changing of direction of the mill paste. This method is used for easily dispersed pigments such as in whites and light pastel colours. High Speed Mixers are used with the continuous mill in order to mix the mixture paste. These mills use a variable speed saw-tooth blade rotating at high speed. Peripheral speeds range from 3000 to 6300 ft/min. High Speed Mixers also have a slow speed sweep agitator at the tank wall to aid in movement from the tank walls.
- 16. Advantages: • They require very little man power to operate it • They are too easy clean-up • Low maintenance costs Disadvantages: • Since the are run by motors, they have a high power consumption • The setup is only limited to easy dispersing pigments • It generates heat during the process of agitating the pigment.
- 17. Sand mill method This mill consists of a high-speed shaft with solid disc impellers rotating off center in a cylindrical tank and it is charged with sand or silica to grind the pigment. Pigments are ground by the tiny particles of sand agitated by the impeller blades and the fineness of the pigment is determined by the duration the paste spends in the mill. Advantages: • It can grind most pigments • Requires low maintenance Disadvantages: • If production is on a large scale it requires many mixes • slow discharge • it is difficult to carry out routine maintenance processes
- 18. Defects of paint Blistering or peeling This is a failure in paint caused by poor or loss of adhesion between the painted surface and the primer coat or between two coatings and this causes the paint film to swell. When the failure is due to moisture, it is referred to as peeling while if it is due to oil or greasy surfaces it is blistering. This can be solved by using emulsion paints that give a porous coating allowing moisture to pass through and not build up between the coatings.
- 19. Checking This is a form of mild form of mild cracking and it is of two froms; one being crazing if it occurs on a small enclosed area or crocodiling if it occurs on a large enclosed area. This is usually due to lack of enough tensile strength especially when the undercoat did not sufficiently dry. It is repaired by cleaning the area affected and applying a fresh coat of paint.
- 20. Flaking This refers to detachment of paint from the surface and this is due to moisture penetration through cracks in the coating. It is prevented by cleaning the surface thoroughly before applying the coating And also one can use plastic emulsion paint.
- 21. Running or sagging This refers to the flow of paint back or towards the unpainted part when it is applied over smooth or glossy area. To avoid this failure, the surface should be cleaned with emery paper prior to painting
- 22. Wrinkling This is also referred to as crawling. It occurs due to the paint film being too thick due to poor mixture proportions or when the oil in the paint is more than the required amount. It is evidenced by the lower part of the paint not drying due to great thickness which eventually shrinks after it has dried.
- 23. Chalking This is a failure in paint that occurs due to insufficient oil in the paint. Flashing This is the appearance of a glossy patch over the painted surface. It is caused by use of sub-standard paints or poor workmanship
- 24. Tests for suitable of paint The scratch resistant test This test is performed in order to determine the resistance of a single coating or multicoated system of paint to penetration by scratching using a hemispherical tipped needle. This test is carried out as a Pass/Fail test to check the compliance of test with particular specification or to determine the minimum load at which the paint is penetrated. Apparatus scratching apparatus
- 25. Horizontal sliding test panel holder Speed motor operating at 30-40mm/s Scratching needle Stop
- 26. Indicating device; this indicates contact between needle and metallic substrate. And this shows that the substrate has been penetrated Needle that has a hemispherical tip of 1mm diameter Preparation of the sample and the test panels Take a representative sample of the product to be tested Examine the sample so that it is ready for testing The substrate is applied onto a 150mm×100mm test panel and allowed to dry The test panels are carefully cut in order to fit on to the panel holder on the apparatus The product under test is then applied on the dry test panel with substrate The test panel is dried for a minimum of 16 hours under a temperature of 210C to 250C and a relative humidity of 45% to 55% The thickness of the coat is determined using a suitable instrument like a micrometre screw gauge
- 27. Procedures Fix the needle in the chuck so that it is perpendicular to the panel holder and balance the needle holder arm using the adjustable counterweight. Clamp the test panel with the coating onto the panel holder. And the longer slide of the panel should be in the direction in which the scratch is to be made. Place the weights onto the holder above the needle to obtain the specified load. Start the motor of the apparatus and allow the scratch to be made in the coating. Observe the indicating device to determine whether electrical contact between the needle and the panel occurs. Remove the test panel and examine the scratch to see if the penetration of a specified depth. The magnification under which the scratch is observed is stated in the test report. The procedure from (i) to (v) is repeated three times on each test panel for each of the two test panels. If the penetration of the scratch in the coating is of the specified depth, the test is reported as Pass and if any of penetration in the six scratches is beyond the specified depth, then the test is reported as Fail.
- 28. Adhesion Test (Cross cut Test) This test assesses the resistant of paint coating to separate from the substrate when a right angle lattice pattern is cut into the coating penetrating through the substrate. Apparatus Cutting tool Single blade cutting tool Multi-blade cutting tool Soft brush Pressure sensitive adhesive tape; the tape should have adhesive strength of 6N per 25mm or 10N per 25mm width Lens of a magnification of ×2 or ×3
- 29. Preparation of the sample and test panel Take a representative sample of the product to be tested and examine it so that it is ready for testing The substrate is applied onto a 150mm×100mm test panel and allowed to dry. If a soft panel is used, it should be of a minimum thickness of 10mm and for a hard panel it is 0.25mm The test panels are carefully cut in order to fit on to the panel holder on the apparatus The product under test is then applied on the dry test panel with substrate The test panel is dried for a minimum of 16 hours under a temperature of 210C to 250C and a relative humidity of 45% to 55% The thickness of the coat is determined using a suitable instrument like a micrometer screw gauge
- 30. Procedure The test panel is tightened or placed in a rigid or on a flat surface to prevent the panel from deforming during cutting of the panel. The cutting edge is then checked to ensure it is sharp enough. It is then held in a position so that it at 900 to the test panel surface. Make the specified number of cuts, maintaining uniform pressure and observing the appropriate spacing between the cuts as indicated below; The spacing between cuts depends on the thickness of the coating Thickness of the coating Spacing Hard Substrate Soft Substrate 0µm to 60µm 1mm 2mm 61µm to 120µm 2mm 2mm 121µm to 250µm 3mm 3mm
- 31. If the hardness of the coating prevents any penetration in the substrate, the test is declared invalid Cuts are made in a direction opposite to the first cuts made in order to have a lattice pattern formed by the cuts. Then brush the pattern lightly using a soft brush in a backward and forward format along the lattices. This is done for a soft substrate but for a hard substrate, adhesive tape is applied over the lattice parallel to one set of cuts made in the substrate. The tape is rubbed firmly using a fingertip and it’s then removed at a steady rate. The cut area is then examined used good lighting with a magnifying lens if possible and the results are classified as below;
- 32. Classification Description Appearance of the cut surface from which flaking has occurred 0 The edges of the cuts are completely smooth and none of the squares has been detached. - 1 Small flakes of the coating detached at the intersections of the cuts. A cross-cut area less than 5% is affected. 2 The coating has flaked along the edges and/or intersections of the cuts. A cross-cut area greater than 5% but less than 15% is affected 3 The coating has flaked partially or wholly in large ribbons along the edges and/or partially or wholly on different parts of the squares. A cross-cut area greater than 15% but less than 35% is affected
- 33. 4 The coating has flaked along the edges of the cut in large ribbons and /or some squares have detached partly or wholly. A cross-cut area significantly greater than 35% but less than 65% is affected 5 any degree of flaking that cannot be classified by classification 4
- 34. APPLICATION OF PAINT For paint to be applied on a surface, the surface should be prepared. Below are the steps taken to prepare a surface for paint. On wood Cleaning; wood surface should be cleared thoroughly. All dust, rough projections and particles of grease, oil and any foreign material removed. Cloth dusters and cleaning brushes may be employed. This can be followed by using sand papers when necessary Knotting; this refers to treatment of knots. Knots are common defects in timber, all these surfaces should be covered and any crack, depressions holes may be filled too. Primary treatment; this is also called priming. It involves giving a rough coat on the timber surface with white lead. This is done to make the timber surface as smooth as possible. Stopping; after the priming coat has dried, the surface is rubbed with help of pumice or fine grade glass paper. This is to remove any irregularities that are yet visible and prepare the surface for the second coat. Application of paint; desired paint is then applied with a brush in two or three or more coats. The subsequent coat is only applied when the previous one has dried.
- 35. On metals Cleaning; metal surfaces are cleaned mechanically. Methods used include; sand blasting, ultrasonic cleaning. Chemical cleaning can also be applied using either an alkaline or acidic medium. Priming; a priming coat is essential for iron and steel painting however for aluminium, zinc chromate is used. Undercoats; the metal then given a coat that is not necessarily enriched with pigment. This is for purposes of hiding the surface under them and also act as a base for the final coat of paint. Finishing coat; the final coat paint must contain all ingredients necessary to give a perfect blend and the best finish to the surface. Application should be done carefully to avoid any defects since any errors may cause the purpose of a paint cover to be lost.
- 36. On cement or concrete surfaces Drying the surface; the surface must be completely dry to achieve a desired effect. Moisture on the surface causes dilution of the paint, retards evaporation and can also start chemical reactions Cleaning; this is done to remove any moulds, fungi or efflorescence patches and any dust deposits Priming Undercoat; Final coat; make sure you use the right paint for priming and undercoating. This is because of the alkaline nature of cement in the plaster or concrete. Oil based paints can deteriorate and thus it’s essential for the surface to be covered by a primer coat of an alkali resistant paint.
- 37. VARNISH Varnish is an almost homogeneous solution of resin in oil, alcohol or turpentine. It dries after applying, leaving a hard, transparent and glossy film of resin over the varnished surface. It is used primarily for wood to give its grains a detailed look, but can also be used on other surfaces.
- 38. CHARACTERISTICS OF GOOD VANISH • It should be fire resistant and of less odour, in accordance with BS 476 part 6&7 1989 • It should render the surface glossy. • It should dry rapidly and give a finished surface which is uniform and aesthetically appeasing. • The colour of varnish should not fade away when the surface is exposed to atmospheric actions. • The protecting film developed by varnish on drying should be tough, hard and durable. • It should have good weathering properties, resist abrasion and wear well. • It should not shrink or show cracks after drying. REASONS FOR VANISHING A SURFACE: • Brighten the appearance of the grain in wood. • Render brilliancy to the painted surface. • Protect painted surface from atmospheric actions.
- 39. PROCEDURE OF VANISHING Preparation of the surface The wood work is made smooth by rubbing it with sand paper and the surface is cleaned. Knotting This is the process of covering the knots in the wood work, using any of the following methods. Size knotting: A coat of red lead ground in water mixed with glue size is applied. After it dries another coat of red lead ground in oil and thinned by boiled turpentine oil is applied. Patent knotting: Two coats of varnish prepared by dissolving shellac in methylated sprit or wine, are used Stopping The surface of the wood work is then rubbed again and cleaned. Before rubbing, the surface is applied with size of hot, weak glue so that pores on the surface are filled up. Boiled linseed oil can be applied in 2 coats. Varnish coats Vanish is then applied in two coats. The second coat is applied after the first has dried.
- 40. INGREDIENTS OF VARNISH • Resins • Solvents • Driers Resins The commonly used resins are copal mastic, amber gum and lac. The quantity of varnish depends much upon the quality of resin used. Copal is considered to be the best, toughest, and hardest and is very durable for external works. Resins can also be made from saps of trees
- 41. Solvents These must suit the resins used. The type of solvent depends upon the type of resin used as summarized below Resin Solvent Amber, copal, gum, amine Boiled linseed oil Common resin, gum dammer, mastic Turpentine Lac, Shellac, Sandarch Methylated spirit Raw copal, cheaper types of resins Wood naptha
- 42. Driers These are added to accelerate drying process and should be added only in small quantities because an excessive damages the varnish and affects its durability. Litharge or lead acetate are the commonly used driers in varnish. TYPES OF VARNISH Oil varnish: is made of linseed oil and takes about 24 hours to dry. Hard resins such as amber and copal are dissolved in linseed oil. If the varnish is found unworkable, a small amount of turpentine oil may be added. It is suitable both for interior and external works. Turpentine varnishes: These varnishes use turpentine as solvent in which soft resins such as gum dammar, mastic and rosin are dissolved. They dry quickly but not so durable. These are cheaper than oil varnish
- 43. Spirit varnish: contains only resin (or some other similar substance) and a volatile solvent. Resins of soft variety such as lac or shellac are dissolved in spirit. The examples are French polish, lacquer and shellac varnish. It dries very quickly. These are not durable and are easily affected by weathering action. Water Varnish: is shellac dissolved in hot water to which enough quantity of either ammonia, borax, soda or potash is added. These are used for varnishing maps and pictures. Flat varnish: are materials such as wax, metallic soap or finally divided silica added to varnish produce a dull appearance on drying. Flat varnish is also thermal insulating Asphalt Varnish: is made by dissolving melted hard asphalt in linseed oil with a thinner such as turpentine or petroleum spirit. It is applied over shop fabricated steel works.
- 44. Polyurethane varnishes: These are typically hard, abrasion-resistant and durable coatings. They are popular for hardwood floors but are difficult or unsuitable for finishing furniture or other detailed pieces Spar Varnish: It derives its name from its use on spars and other parts of ships. It gives sticky effect in warm weather and is not used indoors. Acrylic varnishes: Acrylic varnishes are typically water-borne varnishes with the lowest refractive index of all finishes. They resist yellowing (an aging effect of resins)
- 45. Some common brands of varnish in Uganda
- 46. French polish It is a type of spirit varnish, made by dissolving resin in methylated spirit at room temperature for use on hardwood substances to hide the grain defects. The surface is made smooth by rubbing with sand paper. A filler mixed with desired colour is prepared to the consistency of a paste and applied to the cracks, pores, etc. The surface is rubbed after drying and dusted off. Two coats of polish are then applied. The filler material is prepared by mixing methylated spirit and whiting(ratio3:4) or by mixing Plaster of Paris, red ochre and linseed oil. Wax polish It consists of bees’ wax dissolved in turpentine and is used for highlighting the grain over wooden surfaces. The polish is rubbed over the surface with a rag until a bright appearance is obtained. Generally two coats are applied. It may also be used over marble with a 1:4 mix of wax and hot turpentine, or by mixing wax, linseed oil, and turpentine in given ratios
- 47. MANUFACTURE OF OIL VARNISH Without Resin Oil varnish free from resin, is produced from bodied fatty oil, chiefly linseed oil. Driers and volatile thinners may or may not be added, according to the purpose for which the varnish is used. Varnishes of this type, such as lithographic varnishes, patent leather varnishes, etc., have a more or limited and special use. With Resin: Oil varnish containing resin is produced by adding heated fatty oil to resin which has been previously heated in a kettle until it is completely melted. Driers may be added separately or they may be incorporated with the oil. This mixture is heated until, in the judgment of the varnish maker, it is ready to be cooled and thinned. Heating must be continued until no separation of the ingredients occurs on cooling. By varying mixing and heating methods and temperatures, it is possible to prepare varnishes from the same proportions and amounts of raw materials, but with different properties and qualities.
- 48. METHODS FOR TESTING VARNISHES Having noted whether or not the sample has the desired colour, clearness, and flowing properties, you may then make any of the following tests; Panel Test : Apply a coat of the varnish to a metal or wood panel, which has been painted a dull colour. Note the time required for the film to dry hard; that is, when the finger pressed firmly against the surface leaves no impression. The drying time should not exceed 3 days Let the coat dry for two days or more, and rub with steel wool or powdered pumice and water. Note whether or not the sample has good rubbing properties; that is, whether or not a smooth, doll surface, suitable for the application of a second coat, is obtained.
- 49. Also note whether or not the rubbed surface "sweats"; that is, whether glossy patches form on the panel after twenty-four hours. Apply a second coat of the varnish and let the film dry for three days after it has become hard. The relative lustre of different samples may be noted at this point. Let a stream of cold water run over the varnished surface overnight, and in the morning note whether the film is unaffected, dulled, or whitened. Then let a stream of boiling water flow over the varnish for fifteen minutes and note the effect on the film. A good grade interior varnish should not turn permanently white with water or when wet
- 50. Glass Plate Test: Flow some of the sample on a clean glass plate, allow it to drain and dry in a vertical position, and note the time required for the film to dry "free from tackiness" (the point at which the film no longer feels sticky when touched lightly with the finger), and to dry hard. After five days, run the point of a knife blade through the film at the top of the plate, and note whether it is elastic; that is, whether it comes off as a ribbon from a clean cut, or whether it "dusts" (breaks into small pieces). Elastic varnish is hence undesirable and weak, but that which dusts is hard.
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