Painting and Decorating denotes (a) the occupation or craft of painting and decorating, and (b) the process of applying paint and other materials for decorative purposes. The dual term derives from the fact that the most important function of paint is to preserve a surface (e.g., wood from decay, metal from corrosion) but its use can be extended to enhance the appearance of the surface and make it aesthetically pleasing. This can be seen in the history of Painting and Decorating which goes back to earliest times when the cavemen decorated their caves with murals.
The craft of Painting and Decorating is linked with other building crafts for administrative purposes, but 85 per cent of its work is directed to the redecorating of existing buildings rather than the initial painting of new structures. This is important since the specification for new work almost invariably aims at minimum requirements and rigid economy, producing shoddy work; redecoration calls for a far wider range of skills and a much higher quality of workmanship.
Training is by apprenticeship coupled with technical college instruction. After a basic training a painter is able to prepare surfaces adequately, select the right material for their treatment and apply it correctly for functional purposes. Some men remain at this level and are called ‘brush hands’. Fully trained painters, however, are also skilled in the application of decorative materials and wallhangings. A small proportion develop specialist skills of a high order, such as signwriting, lettering and gilding, graining (imitating wood effects in paint and glazes) and expert paperhanging.
At the highest level a very small number engage in original design, mural painting and heraldic work, and some become interior decorators, designing entire decorative schemes, including the selection of furnishings and fittings.
The trade is loosely organised. The great majority of Painting and Decorating firms are very small units employing 2 or 3 men and operating almost entirely in their own locality, with here and there a larger firm with, perhaps, 25 to 100 men, operating over a wider area. Big firms are few in number and tend to specialise in a highly skilled field such as church decoration or industrial painting, and operate on a nation-wide basis.
As wages continue to rise, the emphasis of the trade changes; the professional painter is increasingly employed on industrial work and the decoration of public buildings, and less often on domestic properties except for well-to-do clients. House decoration is largely done by amateur painters, the owner/occupiers.
Painting and Decorating tools and equipment
Paint is applied by brush, roller, or spray. The most important material for paint brushes is ‘bristle’, a term restricted in law to refer only to hog-hair, which has unique properties. Bristle is expensive and increasingly scarce. Artificial fibre (e.g. nylon) is cheaper and more durable. Cheap vegetable fibre is only suitable for coarse brushes.
Small brushes for specialist work such as signwriting or graining are also made from squirrel, sable and badger hair, etc. Brushes are still essential in Painting and Decorating as they force paint into closer contact with the surface than any other application technique, and give a better quality of finish. Paint brushes range from 1 in. wide and smaller, for cutting-in windows, to 4 in. wide for wall work; brushes for emulsion paint vary from 6-8 in. width.
Rollers consist of a revolving drum covered with a pile fabric, lambswool or sponge rubber and mounted on a handle. On broad areas they are quicker than the brush; they produce a thicker coating, usually a disadvantage, as it is more likely to develop defects such as flaking.
Spray application involves the use of a spray gun in which a trickle of paint is fed into a pressurised air stream which breaks it up into fine particles and blows it on to a surface as a fine mist. Some of the paint rebounds, charging the air with spray dust and causing a fine film to settle elsewhere than on the surface; thus, other areas must be protected and masked.
The most modern method is ‘airless spraying’ whereby the paint is highly pressurised and released without any air flowing – hence there is no spray mist to rebound. All spray application is much quicker than the brush and airless spraying is quickest of all. Spraying is most suited to big areas; on small areas the saving of time is nullified by the time spent on assembling and dismantling the plant.
The painting of mass-produced articles under factory conditions employs many techniques not usually adapted for the painting of structures – e.g., dipping, flow-coating, tumbling, barrelling, hot-spray, wet-on-wet, etc. It is gradually being realised that some of these may have an application to certain aspects of Painting and Decorating, e.g., dipping for wrought iron units such as gantry flooring units in factories, or electrostatic spray for long runs of metal railings. In electrostatic spray, the paint is given a positive electrical charge and the surface to be painted is earthed, so that the paint is attracted to all parts of the surface, giving an even coating with no waste.
The application of wallhangings is a manual operation involving the use of pasteboards, scissors, papering brush, felt-covered roller, plumb-line and folding rule.
In addition to the above, all Painting and Decorating operations call for certain basic tools and plant, such as ladders, stepladders, planks, dust-sheets, buckets, paint cans, scrapers, shave-hooks, trowels, duster brushers, strainers, etc.
Paints used in Painting and Decorating are nearly always of the ‘air-drying’ type i.e., on exposure to the atmosphere they undergo a chemical change from liquid to solid state. Traditional paints consist of pigment bound with vegetable oil medium, plus metallic salts to accelerate drying, plus solvent to bring the mixture to a workable consistency: the medium most often used is linseed oil, which combines with oxygen in the air and gradually solidifies by the process of oxidation.
Such paints have their place but in present-day practice the medium used in most paints is a more sophisticated material consisting of synthetic resins blended with heat-treated oils. One of the resins most frequently used is alkyd resin which combines great hardness and flexibility with good colour retention; among other resins used are phenol (resistant to alkaline and corrosive conditions), couma-rone (good chemical resistance) and epoxy resins (which are very hard and elastic and strongly resistant both to abrasion and chemical action).
The resins are blended, according to requirements, with varying proportions of such oils as tung oil, dehydrated castor oil, etc. The drying process of these media is largely one of ‘polymerisation’ producing coatings which generally dry more rapidly than the traditional media (with less risk of the film being damaged by dust or rain), are harder and more durable, and have greater gloss retention and resistance to chemical attack.
There are also two-pack materials such as the polyurethane finishes; in these the resin is mixed with a catalyst or curing agent immediately before use; the coating rapidly dries to a finish as hard as that of a stove-dried enamel such as is used on cookers and similar appliances. The result is a coloured paint or clear lacquer with extreme hardness, flexibility and resistance to chemical attack, applied like any other household paint.
A wide range of special paints is available to suit particular purposes. There are heat resisting paints for boilers and radiators, fire-retarding paints to reduce fire-risk, anti-condensation paints for kitchens and canteens, fungicidal paints to check mould and fungus growth, anti-corrosive paints for metals, chlorinated rubber paints to resist chlorine attack in swimming baths and the destructive agents found in dairies, bottling plants and laboratories, as well as primers and sealers to suit every type of surface.
Bituminous paints are available in many forms for use on structural steelwork, water pipes, tanks, vats and food containers. There are multi-coloured paints which provide a speckle finish in several colours in one application. Materials of special interest to the amateur are the non-drip or thixotropic paints. These are so thick as to be virtually non-spillable even when the container is overturned. They are not stirred before use. The brush is dipped into the thick paint and then transferred to the ceiling or wall surface; the shearing action of the brush makes the paint become thin and reduces it to a workable consistency so that it spreads in the normal manner. After application the paint soon thickens again, thus preventing any tendency to run, and it dries like any conventional paint.
A good painting system must consist of several coatings – a primer appropriate for the particular type of surface, undercoats to give film thickness and opacity, and a finishing coat to provide a full-gloss, semi-gloss or matt finish resistant to local conditions of exposure.
Water thinned materials
Distemper is now obsolete. Water paint, consisting of good quality pigments bound with emulsified oil and thinned with water, gives excellent results on plastered surfaces, but its use is declining. The most widely used material for ceilings and walls today is emulsion paint, which is made with good quality pigments bound with synthetic resin and thinned with water. The characteristics of emulsion paint are (a) ease and speed of application – hence low labour costs (b) rapid drying, permitting two or even three coats to be applied in one day, (c) rapid hardening, giving a surface which withstands scrubbing (d) tolerance of damp and (e) resistance to alkaline attack, making it suitable for use on new plaster, cement, asbestos and similar surfaces.
Of the many resins used, polyvinyl acetate is the most popular. Acrylic resins are being increasingly used; they give extremely rapid drying and produce a hard film resem bling perspex. Acrylic emulsions are now being produced for the painting of woodwork.
Preparation of new work for oil paint
Wood. The wood must be dry. Remove all dirt and grit, sandpaper down, dust off, apply two thin coats of shellac knotting to seal knots, apply primer. The primer for softwood should be oily to satisfy absorption, and the primer for hardwood should be thinned in order to assist penetration; in both cases, best quality lead-based paint is the most satisfactory. For resinous woods (Columbian pine, etc.) use aluminium primer to seal the resin. For oily woods (cedar, teak, etc.) wash wood with acetone. When the primer is dry, stop all holes with putty, on good quality work apply paste filler and rub down smooth.
Iron -and steel. Remove all rust and mill-scale, either by flame-cleaning or shot-blasting (expensive but effective) or by manual methods of chipping and wire brushing (slow, tedious and often inefficient). Prime without delay with rust inhibitive primer, e.g., red lead, zinc chromate, zinc-rich, etc.
Non-ferrous metals. Degrease, etch, prime with zinc chromate or calcium plumbate.
Plaster, asbestos sheeting, concrete, cement. Must be dry. Clearf off dirt, grit, etc. Apply two coats of alkali-resisting primer. Gypsum plaster should be inert, but may be activated by the backing material; it is safer to treat it for alkalinity. Keene’s cement and hard-burnt anhydrous plasters are often too smooth for paint to adhere; a procedure called ‘following the trowel’ is effective.
Wallboards. Some types are supplied ready for immediate painting; very absorbent boards should be sealed with a thin coat of emulsion paint.
Foamed polystyrene. Coat with thin emulsion paint; never apply oil paint direct.
Preparation of old surfaces previously painted
Wherever possible, avoid removing the existing paint film. The choice of the most appropriate type of preparatory process is governed by an assessment of the condition of the surface. If the existing paintwork is perfectly sound it should be cleaned down by the most suitable method, with particular care paid to the removal of grease, e.g., on woodwork, wash down with a weak solution of sugar soap, rub down with a pumice block or waterproof sandpaper, rinse thoroughly with two changes of clean water.
On walls and ceilings, wash with a weak detergent or sugar soap solution, and on wall work be careful to commence washing at the base of the work and work upwards, then rinse off with several changes of clean water; on iron and steel, avoid wetting the surface if possible, use degreasing agent where necessary, remove all traces of rust, and inspect the surface for indications of rust spots developing beneath the paint film, pay particular attention to bolt-heads and rivets, paint immediately after cleaning.
For other surfaces generally, treat as for walls. Where the existing paintwork is defective, in the case of serious faults such as blistering, cracking, flaking and peeling the paint must be removed. Paint removal from woodwork is best carried out by burning off, using blowlamps or bottled gas and blowtorches, taking care to avoid scorching the wood. On plaster and metalwork, burning off is completely ineffective; the film is removed with a spirit paint remover, after which the surface is washed with a solvent such as white spirit. On steelwork either a caustic or a spirit paint remover is suitable. In the case of mild faults paint removal is not necessary. If the paint is chalking the surface should be well rubbed down with dry sandpaper (unless it contains lead in which case wet rubbing is essential). When the preparation is complete, treat stripped surfaces as new work and proceed accordingly.
Oil paint should be brushed out to a thin, even coating; thick coats must be avoided as they lead to softness in the paint film and ultimately to cracking. After spreading the paint, lay it off with light strokes to eliminate brushmarks.
Preparation for emulsion paint
See that new surfaces are reasonably dry; apply a thinned coat of emulsion paint to check porosity, then apply a second coat unthinned. On existing work, remove any grease from the surface, and scrape off any loose or flaking paint; if necessary bind down with a proprietary brand of sealer. All water-thinned materials should be applied in a good full coat; do not attempt to brush out thinly.
Paints consist of finely powdered, insoluble materials, principally pigments suspended in liquid binding media, and possess the property of drying to adherent films on exposure to the atmosphere or the application of heat. They are used for the decoration and protection of all types of articles and buildings, and for artistic purposes. The principle function of pigments is to impart colour and opacity, although there is a further group of materials, known as extenders, which are often loosely classified as pigments.
The most common extenders are ground barytes, blanc fixe (precipitated barium sulphate), asbestine (fibrous talc), china clay and whiting (calcium carbonate); and whilst they impart little or no colour or opacity, they are widely used to lower raw material cost. Providing this is not carried to excess, no harm results; indeed, in certain circumstances the presence of extenders may strengthen the film of paint and even improve its durability.
Binding media used in paints
Binding Media consist of drying or semi-drying oils and/or resins and are thinned, if necessary, with suitable solvents such as turpentine, white spirit (turpentine substitute), the coal-tar-hydrocarbons (benzol, toluol, xylol and naphtha), or, in the case of special paints, with certain alcohols, esters, ketones and chlorinated hydrocarbons.
Linseed oil is still used in some paints, although large quantities of tung oil (Chinese wood oil) and dehydroxylated castor oil are also used. Tung oil dries more rapidly than linseed oil and is more water- and chemical-resistant, whilst dehydroxylated castor oil has a degree of chemical and water resistance approximately half-way between the two; it also yellows much less on exposure, but tends to dry with a film which remains tacky for a long time.
A number of other oils such as perilla, soya bean, oiticica, stillingia, sunflower seed, hemp-seed, tobacco seed and various fish oils are also used to some extent. It is nearly always necessary to process such drying oils by refining or by heat treatment in order to improve their performance. Heat treatment increases the viscosity of the oil, usually by partial oxidation and by polymerisation (a chemical process in which molecules of the same compound associate to form more complex molecules). Such treatment can profoundly affect flow, gloss, durability, chemical resistance and drying time whilst removing such undesirable properties as ‘ropiness’ (the showing of brushmarks), wrinkling and after-tack. It also permits a greater addition of solvent, thus lowering the price of the finished paint.
The use of resins in paints
Resins used in paint can be classified as either natural resins or synthetic resins, although the former have to a very large extent been replaced by the latter. The commonest natural resin is rosin (colophony) , which is- the residue remaining after the distillation of turpentine from the exudation of the pine-tree; wood rosin is obtained by solvent extraction from old stumps of pine-trees.
Whilst rosin can be used on its own in oils to form paint media, this is done only in the manufacture of the cheapest paint Its performance can, however, be much improved by reaction with lime, zinc or glycerine, by hydrogenation and polymerisation, and by reaction with synthetic resins. The other main class of natural resins are the copals. These are derived from fossil or more recent forest remains, and usually bear the name of the district of origin, e.g. Congo copal or Sierra Leone copal. Nowadays these are mainly used in varnishes .
The earliest synthetic resin used in paint was made by reacting phenol with formaldehyde and combining the resultant resin with rosin in order to obtain solubility in oil. It was subsequently found that, by using more complex phenols, the rosin could be dispensed with, this resulting in resins having greater durability and water and chemical resistance. These phenolic resins can be dissolved in or combined with drying oils to form media having good durability, gloss and resistance to water and chemicals.
The most important class of synthetic resins is the alkyds. These are made by reacting glycerine or pentaerythritol with phthalic anhydride and drying oils. Other modifications can also be made, such as the introduction of phenol or rosin. The alkyd resins give paint of the highest durability, of excellent gloss retention and good drying properties. They are also used in the manufacture of industrial finishes either on their own or, for stoving finishes, in admixture with urea resins (urea reacted with formaldehyde), or with melamine resins (melamine reacted with formaldehyde).
Combinations of polyamide resins with alkyd resins are used to produce thixotropic, or gel paints, which have a thick, jelly-like consistency, and thus do not drip from the brush, but which flow under the action of brushing to give an even film.
Recently, the development of new synthetic resins with improved properties has led to paints formulated without any oil component. The resin is either dissolved in a suitable solvent, which evaporates to produce the paint film, or is liquid in its original state, hardening by chemical reaction in the film. Common examples of resins used in solvent-based systems are acrylic resins (polymers of acrylic acid derivatives) and polyvinyl acetate derivatives.
In the second category, used in the so-called solventless paints, polyurethanes (polyesters reacted with isocyanates) and epoxide resins (epichlorhydrin reacted with diphenylolpro-pane) are most frequently used. Paints of the solventless type are often of the ‘two-pack’ variety, in which the two reactive components are separated, and mixed immediately before application. Single-pack polyurethane paints are also manufactured, the hardening reaction being initiated by contact with moisture in the atmosphere.
The newer synthetic resins are also used in conventional oil-based paints to improve their properties; to some extent, however, oil-based paints are being superseded by the newer types of formulation.
Driers must be added to paint containing drying oils in order to accelerate the drying process. These are catalysts which increase the rate of oxidation or polymerisation of the oils. The driers used are usually the organic salts, such as the resinates, linoleates, naphthenates, or octo-ates of lead, cobalt and manganese, although other metals, such as iron, vanadium and cerium, can be used.
Water paints basically follow the above pattern, except that water is used in place of organic solvents, and additions of water-soluble or water-dispersable substances may be made. Distempers contain white pigment, usually lithopone, and whiting and may be bound with glue (non-washable distemper) or casein (fast-bound distemper). Oil-bound distempers contain glue and/or casein into which oil and/or resin is emulsified. Plastic emulsion paints are water paints based on emulsions of synthetic resins such as polyvinyl acetate or polystyrene, and are characterised by excellent washability and resistance to lime.
Manufacture of paint is carried out mainly in two types of machine. The ball mill consists of a horizontal cylinder lined with steel or porcelain and containing a charge of steel balls or pebbles. The paint and the balls are turned round for a number of hours until the pigment is properly dispersed. Other mills are based on rollers which crush the mixture of oil and pigment between them, whilst refining is carried out by means of a single roll mill which causes the paint to pass between the roller and a fixed iron bar.
The development of surface treated pigments which have easier dispersion characteristics has led to the use of a third type of machine. The high speed mixer is basically a shaft rotating at high speed, at the end of which is a system of vanes or blades immersed in the paint. The blades are so designed as to produce a high shear force in the fluid base, and the pigments are virtually ‘stirred-in’ to form the paint.
The term includes not only an immense variety of wallpapers but also a wide range of fabrics, veneers, relief goods and plastic and metallised panels.
Wallpaper is made from wood pulp and is supplied in rolls. The paper itself may be processed in some way irrespective of its colouring; it can, for instance, be embossed to provide relief (and in the case of a heavy emboss two layers of paper may be pressed together to form a Duplex paper) or it can have wood chips or fibres introduced during manufacture to impart a rough texture when it is called an ingrain. The paper may then be coated with a ground colour and a coloured pattern superimposed, or in cheap pulp papers the pattern is printed directly on the raw paper. Naturalistic or abstract patterns are printed in opaque water colour and sometimes parts are printed in bronze or other metals.
Most wallpaper patterns consist of a combination of several of these processes, and the permutations are almost unlimited. Thus there are satin and chintz patterns, shiny mica papers, imitation leathers, plastic paint effects, wood grains, soirettes which are self-coloured satins in low relief, moires which have a watered silk effect produced by delicate embossing, jaspes with a soft irregular combed appearance, and many others.
Most wallpapers are machine printed to keep them within a reasonable price range, but hand prints are available for those requiring distinctive patterns. Flock paper has been produced for centuries and is still highly popular – its pattern of raised pile is produced by blowing silk, wool or nylon trimmings on an adhesive ground, to imitate velvet or tapestry.
There are also exotic papers such as Japanese grass-papers, Dutch metallic and damask effects, Scandinavian hangings with layers of polished wood strips in variegated colours, Spanish papers with thin shavings of cork attached, and Japanese wood veneers. Many modern English papers in the medium price range are coated after printing with a film of vinyl resin which makes them extremely tough and washable. Pre-pasted papers were introduced from the U.S.A. in 1961 but made no impact; they were, however, rentroduced successfully in 1971; the back is coated with an adhesive which is activated by pulling the paper through a trough of water.
Until recently all wallpapers had a selvedge which needed trimming off before they were hung; today most papers are supplied ready trimmed.
Anaglypta and Lincrusta are examples of relief goods. Anaglypta is a high-relief hollow backed paper made from rags; it is sold in rolls or panels to give geometric patterns, random swirl patterns, sculptured effects, imitations of ashlar or pebbled stones, etc., and it is painted after hanging. Lincrusta is a low-relief material made from oxidised oil on a smooth paper backing, and is chiefly known for its wood-grain effects though it is also produced in other patterns; it is stained and varnished after hanging.
Fabrics are increasingly used as hangings and these range from very fine decorative ones to coarse utilitarian materials. Fine silks are applied dry, stretched tightly over wooden frames. Linen, canvas, hessian and jute are available in many forms, either in natural hue or attractively coloured; some have a stout paper backing while in other cases the fabric is fastened directly to the wall. Some have a self-adhesive backing which is exposed by removal of a protective backing sheet. Some are painted after hanging.
Fabrics generally are hard-wearing and durable, do not show pin-holes, and form a good background for pictures, pottery, etc. Coated fabrics include rexine and American cloth but the type most frequently used are the vinyl coated fabrics which are extremely durable and resistant to chemicals and detergents; they are supplied in varying widths and an attractive range of patterns.
Other hangings include plastic panels for decorative use and polystyrene panels and tiles for thermal insulation.
Each of these many materials has its own techniques of application and presents its own particular problem. The skill of Painting and Decorating consists in choosing the right method, selecting the correct type and strength of adhesive and generally adopting the most effective procedure.
Preparation for Wallhangings
On new surfaces, make sure the work is perfectly dry. Sandpaper down. If there is any possibility of chemical action, apply alkali-resisting primer. For good quality papers and relief goods, coat the surface with weak glue-size, and hang a lining paper, using flour-based paste. For most of the inexpensive papers, apply weak glue-size but hang paper without lining; if cellulose paste is used do not use glue-size but use thinned paste instead. For vinyl papers no lining is needed but the correct paste containing fungicide must be used. For special materials, follow the directions supplied about use of coloured linings, applying dry materials to a pasted wall, correct choice of adhesives, etc.
On old surfaces, remove the old paper, wash the surface thoroughly to remove all traces of size and paste which might putrefy; make good all cracks with plaster of Paris or filler, sandpaper down; then proceed as for new work.
The hanging of wallpapers is usually commenced at the main window opening and proceeds outwards towards the door. Plumb the first length on each wall to make sure it is vertical. Absolute cleanliness is essential at every stage. Normally, papers are smoothed in position with a papering brush, but for delicate papers a felt covered roller is preferred.