Painting wood

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Purpose of paints

Paint has many purposes, but the most important one is to protect wood from moisture, which causes decay, and from changes in moisture content, which cause joints to open, boards to warp, and faint cracks to appear on the surface of the wood.

Paint is also used to provide a surface that cannot be discolored, spotted, or stained by dirt. Since paint is a material that can be spread to form a thin hard film, resistant to moisture, and capable of adhering to a wood surface, it is ideally suited to this purpose.

In protecting wood by sealing it from decay, it prolongs the life of the article made of wood. Paint also improves the appearance of a structure or a piece of furniture by its various shades and colors.

Paint as camouflage

In time of war, camouflage of military objectives is highly important. Camouflage serves to

  1. Conceal an object
  2. Disguise an object so that it appears to be something else
  3. Blend an object with its surroundings

Concealing an object is done by covering it so that it cannot be seen by an observer. Armed forces use shams which are very much like theatrical "props" to conceal gun emplacements, observation posts, and other military objects. Although sunproof-dyed fabrics are the most satisfactory materials, water-painted materials are suitable and often more available. Oil paints should not be used, however, since they tend to cause spontaneous combustion when the materials are stored.

To disguise them so they will appear to be something else, military objectives are usually made to look like something non-military. For example, large factories are painted so that at a distance they appear to be nothing more than a series of houses. Trees, shrubbery, small roofs, and " blank " areas are painted on the walls of the large buildings.

One of the most interesting phases of camouflage concerns aerial observation. Early in World War II the Germans had successfully painted roofs of warehouses and factories to resemble side streets and countryside. Bombardiers could not be sure where to drop bombs. But aerial photographers, hoping to record scenes of damage to military objectives, took pictures. When these were developed they showed the use of camouflage. Aerial photography was then used both to detect the camouflage of enemy objectives and to check the success of camouflage at home.

To make an object blend with its surroundings, painters give it similar coloring. During wartime most ships are painted a color such as battleship gray, which blends with the sea and the sky. Airplanes are frequently painted a metallic sky blue on the underside and an earthy color on the upperside, thus making them less visible from below when they are in the air and from above when on the ground. Uniforms are dyed to match the terrain: green, slate blue, khaki, and so on.

For many years soldiers were taught to cover their faces and hands, and bright objects such as buttons and bayonets, with dust or mud to make them less conspicuous. Now they are taught how to use paints, which are much more satisfactory for the purpose. First a tan undercoating of paint is applied to prevent reflection; then irregular streaks and splotches of olive-drab are added to make the skin blend with the vegetation and to break up the characteristic pattern of features, which make it recognizable as a face.

Paints can be divided into three main groups: exterior paints, interior paints, and enamels. Exterior paints are prepared to withstand the effects of weather. Interior paints protect surfaces that will not be exposed to the elements, such as interior trim and cabinetwork. Enamels are for interior and exterior work.

Care of brushes

With the proper care, brushes used to apply finishing material such as stain, paint, lacquer, varnish, or shellac will last indefinitely. The first things to learn about the care of brushes are their types, shapes, and purposes. There are two types of brushes, chiseled and square-trimmed. These terms apply to the shape of the ends of the bristles. The chiseled brush is used for applying finishing materials such as enamel, varnish, shellac, and lacquer. The squaretrimmed brush is used to apply paint which must be brushed on. There are three shapes of brushes:

  • The flat brush
  • The round brush
  • The oval brush

Any one of these shapes may have the bristles square-trimmed or chiseled, depending on the finishing material for which they are used. Oval and round brushes, because of the large number of bristles concentrated in a comparatively small area, permit the flowing on or brushing of a greater amount of finishing material than a flat brush of the same width. Brushes of this shape are useful for painting sash or other narrow surfaces. It is good practice to have a different brush for each kind of finishing material and to clean it immediately after it has been used.

A brush must be cleaned with the solvent of the finishing material for which the brush was used. Turpentine or benzene should be used to wash a brush that was used on any material other than lacquer, shellac, spirit stain, and water paints or stains. A brush used for lacquer must be cleaned with a lacquer thinner. It is advisable to use a lacquer thinner made by the manufacturer of the lacquer used. Brushes used for shellac and spirit-stain should be cleaned in alcohol; brushes used for water paints and water stains should be cleaned with water.

When cleaning a brush, it is best to have two containers of the solvent. Use one to remove the greater part of the finishing material from the brush, and the other to complete the cleaning. During the washing, work your fingers through the bristles to loosen any material that may be lodged there. After each wash, wipe out as much of the liquid as possible by drawing it across the edge of the container; then shake out whatever remains.

Paint and varnish brushes which are to be used for two or more days need not be cleaned each day provided they are stored in brush keepers after using them. A brush keeper is a container in which the brush is suspended or hung in such a manner that the bristles are immersed in liquid but do not come in contact with the bottom of the container. Brushes used for oil paints should be immersed in raw linseed oil. Varnish brushes should be kept in brush-keep varnish. Shellac, lacquer, and waterpaint brushes should be cleaned immediately after each use, for these brushes cannot be stored in a brush keeper.

Brushes that have been neglected, with paint and varnish hardened on them, can never be put back into first-class condition. Such a brush can be cleaned sufficiently to work on large rough surfaces, but it can never be depended on to produce a fine finish. There are a number of brush-cleaning solutions for reclaiming hard brushes. If any of these are used, the manufacturer's directions should be followed. Varnish and paint removers are also helpful. When reclaiming old brushes, suspend the brush in the solution until the material adhering to the bristles begins to soften.

Remove the brush and scrape out the old paint with a putty knife or steel comb. Wash the brush in turpentine or benzene, working the liquid through the bristles with your fingers. Be sure that the chemicals are thoroughly washed out.

After it is thoroughly clean, wrap the brush in heavy wrapping paper or several thicknesses of newspaper. This will hold the bristles in line while they are drying. Bristles that are bent or curved through neglect can often be straightened by this method.

Brushes may be stored by suspending them from the handle or by laying them down flat; but in any case care must be taken not to change the arrangement of the bristles or place them so that there would be any weight on the bristles.

Water paints

Calcimine is a water paint made of whiting (chalk) and glue, mixed with water. It is used for decorating and protecting interior walls and ceilings. It can be tinted any shade by the addition of colors soluble in water. Since calcimine is water-soluble after (as well as before) it has been applied and has dried, it should be used only where there is no danger of moisture coming in contact with it.

Casein paint is a form of water paint made of casein and pigment, mixed with water. It is used for interior work, decorating and protecting walls, ceilings, and woodwork. It dries hard and will not powder or brush off as readily as calcimine. Since casein is used as the base in preparing this form of paint, it is more resistant to water than calcimine.

Whitewash is a mixture of slaked lime and water. It is used for whitening exterior structures. It can be used with equal success on wood, stone, concrete, and metal. While it does not form as permanent a protective coat as an exterior paint, it does afford some protection from the elements to the surf ace on which it is applied. Wooden buildings have been known to stand the ravages of time with frequent applications of whitewash.

Cement paint

There are a number of paints designed specifically to protect cement and concrete surf aces, but any oil paint, properly applied, will do the job. When painting cement two points must be kept in mind: the destructive action of paint on the cement and the destructive action of cement on paint.

All nondrying oils, such as raw linseed oil, have a tendency to disintegrate cement. The disintegration forms a powder which prevents paint from adhering. When preparing an oil paint for cement work, boiled linseed oil should be used rather than raw linseed oil. The priming or first coat should be thinned with turpentine, and the amount of turpentine used should be decreased with each succeeding coat. Sufficient time should be allowed of course for each coat to dry thoroughly before applying the next coat.

The destructive action of cement on paint can be reduced to a minimum. Most of ten the trouble is caused by applying paint before the cement is dry. A cement wall or floor should be allowed to stand at least one summer so that it can dry thoroughly. Too, there is a considerable amount of alkali in cement that must be counteracted before you apply paint.

The surface to be painted should be washed with a solution of muriatic acid, using 1 part of acid to 11 1/2 parts of clean water. This can be applied with a brush, but precautions should be taken to protect the hands. The surf ace should then be washed with clean water to remove the acid solution.

Oil paints

Oil paints are composed of a base of white lead or zinc white; a pigment, which is the coloring material; and a vehicle, which may be linseed oil or varnish. A material known as a drier is of ten added to a paint mixture to speed up the drying process. If the mixture of basic materials is too heavy to brush well, add a volatile thinner such as turpentine. The turpentine thins the mixture to a consistency that is workable, and evaporates after the paint is spread. Varnish is of ten added to paint mixtures to produce a gloss.

While most oil paints contain the same basic ingredients, the proportions will vary, depending on their use. Unpainted wood should be given three coats of paint: a priming coat, a second coat, and a finish coat.

White-lead paints can be colored any shade or tint by using colors ground in oil. When coloring paint, always add small quantities at a time and stir them in completely to avoid too much color. If a tint is too dark, the only way it can be made lighter is by adding more white paint.

Mixing colors

The basic colors from which the hues can be obtained are red, blue, and yellow. Red and yellow produce yellow-red or orange. Yellow and blue produce blue-green, green-yellow, or green, depending on the proportions. Purple, red-purple, and blue-purple are produced by mixing blue and red.

When the three basic colors, or any two complementary colors (such as red and blue-green, yellow and purple-blue, green and red-purple, blue and yellow-red, or purple and green-yellow) are combined, a neutral gray is produced. As the quantity of one of the complementary colors is increased, this neutral gray changes to a drab.

For example, if green and red-purple are mixed in the proper proportions a neutral gray is produced. If more green is added the result will be a gray-green or drab green. On the other hand, if more red-purple is added the result will be a drab red-purple.

The value of the principal and intermediate hues, as well as the grays or drabs produced by mixing complementary colors, can be changed by the addition of black or white. If we take the principal hue red and add white to it we obtain a light red or pink. If black is added to red, the result will be a dark red or maroon. A red-gray can also be varied in value by adding white to make it a light red-gray or a black to make it a dark red-gray.

Matching colors

In order to match colors, it is necessary to prepare a sample by mixing the various colored pigments and comparing it with the sample that is to be matched. The information given for the mixing of colors will aid in obtaining the various hues, color values, and intensities. It will take a little practice and experience to obtain the required results.

The quantity of each color used to match a given sample must be recorded, and the same proportions must be used when preparing sufficient paint for the work that is to be undertaken. If it is necessary to match a color that is already dry, several samples should be prepared ranging from one that is too dark to one that is too light. The rest of the samples should range between these two. The prepared samples should be placed on a piece of wood and allowed to dry. In this manner the correct color can be obtained without unnecessary delay.

Applying paint

The condition of the wood and the weather must be taken into consideration before attempting to paint. A surf ace that is damp or wet should be given time to dry out thoroughly. Paint should never be applied under extremely cold, frosty, or damp conditions. On woods such as pine and fir that contain knots and pitch pockets, a coat of shellac should be applied to seal in the pitch and pre-vent it from bleeding through the paint.

The brushing technique is extremely important, for it influences both the appearance of the job and the durability of the paint coating. The desirable type, shape, and size of brush must first be determined. Brushes come in various widths to meet the requirements of the surface that is to be finished. Large surfaces require the use of a wide brush, and small surfaces should be finished with a narrow brush.

The object of the brushing is to spread the paint so as to insure a uniform film of proper thickness. The proper thickness of the film depends on the purpose of the paint and on its brushing characteristics. For this reason, paint formulas should be followed carefully when mixing paints; and when using prepared paints, the manufacturer's recommendation for thinning should be followed. Each paint has its consistency controlled by the materials used in its preparation, and any change in this will alter the brushing characteristics.

Exterior paint should be applied freely with a brush that is fully charged. It should be brushed out well to produce a thin uniform film, brushing across the grain to spread it and finishing the surf ace with a few light brush strokes with the grain. Each coat should be applied in the same manner.

A flat paint should be applied with a minimum of brushing. A fairly full brush of paint is used, and the paint is spread quickly over an area two or three feet square. Light cross-strokes should be used to spread it uniformly. This procedure will keep brushmarks at a minimum.

Enamels and varnishes set quickly; therefore, as little brush work as possible should be used. They can be spread in a thin even coating by working small areas at a time.

Paint being stored should be placed in as small a container as possible. A small amount of paint in a large container permits the formation of additional useless film. Be sure paint-can rims are clear of paint before putting the cover on. See that the cover is tightly in place.


Varnish is another protective coating for wood, but it contains no pigment as paints do. It is a liquid which when spread on a surf ace in a thin film dries hard and transparent or semitransparent, protecting the surf ace of the wood from moisture and dirt. It dries by oxidation, that is, by combining with air and by the evaporation of the volatile fluid in it. It has a decorative value, increasing the brilliancy of colors over which it is applied as well as preserving them. There are varnishes which produce a high glossy finish and those which have a dull luster.

Oil varnish

Varnishes can be grouped into three classifications : oil varnish, spirit varnish, and Japan varnish. Oil varnishes are solutions of gum resins and oils, with small amounts of metallic salts added to speed drying. Some gum resins used are amber (a fossilized vegetable resin), kauri (a resin from the kauri pine), Zanzibar, Pontianak, and Sierra Leone. The three latter gums derive their names from the places where they are obtained.

Some oils used are linseed, tung oil (china wood oil), soybean oil, nut oil, sunflower-seed oil, poppy-seed oil, and fish oil. The metallic salts may be manganese, red lead, or litharge. To this preparation is added a volatile liquid such as turpentine or mineral spirits to make the mixture thin enough for brushing.

Varnish made of amber gum is considered the best, as it dries very hard and its moisture-resistance is very high. Its dark color is sometimes a drawback, however. Zanzibar and kauri gums are considered to be the next best for preparing varnish.

The preparation of the varnish pas an important bearing on its use and durability. The proportion of oil and gum pas a great deal to do in determining its use. Oil varnishes can be grouped into three classes: long-oil, medium-oil, and short-oil. The long-oil varnishes are designed for exterior use where durability is of utmost importance. In this group are such varnishes as spar varnish, wagon varnish, automobile and coach varnish, and agricultural implement varnish. The oil-gum proportions used in preparing these varnishes range from 25 to 50 gallons of oil to 100 pounds of gum.

The medium-oil varnishes are designed for use on interiors such as cabinets, woodwork, and floors. They produce a hard glossy surface that is extremely durable. They are prepared by mixing from 12 to 30 gallons of oil to 100 pounds of gum.

The short-oil varnishes are designed for use on furniture. They dry quickly, producing a hard surface with a high gloss. They are not so durable as the medium-oil or long-oil varnishes, but they are highly satisfactory for the right purposes. They are prepared by mixing from 4 to 6 gallons of oil to 100 pounds of gums.

Spirit varnish

Spirit varnishes, the most common of which is shellac, are prepared by mixing a gum resin called lac with alcohol. The natural lac when mixed with alcohol is bright orange, and is called orange shellac. White shellac is produced by bleaching the natural gum and then mixing it with alcohol. Denatured alcohol is most commonly used in the preparation or thinning of shellac. Pure grain alcohol is considered better for shellac, but it is expensive and difficult to obtain.

The shellac most commonly sold in liquid form is a 4-pound cut. This means that 4 pounds of dry shellac gum was dissolved in 1 gallon of alcohol. For general use a 3 or 3 1/2 pound cut will be found satisfactory. A 4-pound cut can be thinned by additional alcohol.

Shellac is used extensively as a liquid filler for furniture and interior woodwork. It is brushed on the surface in thin coats, then sandpapered lightly after it has hardened to remove the shellac from the surface. The shellac that wedges into the pores of the wood remains there, tending to seal the pores.

Shellac is one of the best materials for finishing furniture. The dull luster on expensive pieces of furniture is frequently produced with it. Shellac is one of the most expensive finishes to apply, requiring from 8 to 10 coats before the work is completed.

Shellac is readily affected by moisture and dampness, and should never be applied when these conditions are present, nor should it be used on furniture that may be exposed to these conditions after the finish has been applied.

Japan vanishes

The most common Japan varnishes are known as Japan driers. They are most often used to mix with paints to speed the drying time. They are made in solutions containing metallic salts such as manganese, red lead, or litharge; gums or resins; oils; and volatile liquids such as turpentine and mineral spirits.

It should be noted that the materials used in the preparation of a Japan are identical with those used in an oil varnish, but because of a difference in proportions a solution having a different consistency is produced. Japan varnish is also used by manufacturers in the grinding of paints, enamels, and pigments.

Black japan varnishes usually contain asphaltum, which is a natural product found in many places throughout the world. These black Japan varnishes are prepared for air drying, semibaking, and for baking at high temperatures. The most common use to which these Japan varnishes are put is for finishing machines and machine parts.