Instructions Of Painting On Exterior Surfaces Part 1
For exterior wood and metal surfaces, painting should be done only in clear dry weather and generally the temperature should not be below 50° F. When the weather is cold, work should be stopped early enough in the afternoon to allow the paint to set before a sudden drop in temperature occurs. Woodwork should be thoroughly dry and seasoned before paint is applied. Temperature conditions should be the same for painting exterior masonry as for wood and metal. Masonry surfaces must be dry if oil base paints are to be used, while other masonry paints such as cement-water and resin-emulsion may be applied to damp surfaces.
Sufficient time should be allowed between coats so that the paint film will dry hard before more paint is applied. Oil paints on exterior wood should dry at least 24 hours, several days' drying time being preferable.
Two-Coat Paint System
A minimum of three coats was formerly the accepted practice for initial painting on exterior wood, and this practice is still largely followed. However, by using special primers, two-coat paint systems for wood have been developed that are durable and satisfactory. The principle of the two-coat paint system is that as much paint is applied in two coats as normally would be applied in the three-coat method of painting. On smoothly planed wood, the usual spreading rate for three-coat painting is about 550 to 600 sq. ft. per gallon for the first or priming-coat paint and about 600 to 650 sq. ft. per gallon for each of the next two coats. In the two-coat paint system, the primer is spread at the rate of about 450 sq. ft. per gallon and the finish coat about 550 sq. ft. per gallon. Rough surfaces and weather-beaten wood require much more paint than is indicated for smoothly planed wood.
Three-Coat Paint System
Mixed-pigment prepared paints are available for three-coat work, in addition to linseed-oil white-lead paints which may be mixed on the job or purchased ready-mixed. The manufacturer's directions should be followed in thinning the first and second coats. It is sometimes advisable in moist atmospheres, particularly at the seashore, to add a small amount (1 pint to a gallon) of good exterior varnish to the top coat of paint. The varnish should first be tried in a small amount of paint to make sure that the two are compatible and that the varnish will not cause the paint to thicken.
Shingle Stains
Shingle stains are pigmented oil stains, similar to very fluid paints, which can be applied by dipping, brushing, or spraying. They are intended for application to comparatively rough exterior wood surfaces where it is not necessary to bring out the grain and texture of the wood to which they are applied, and they dry to a matt or semi-transparent finish. Durable pigments, such as iron oxides, are used for the colors red through brown; chromium oxide, for green; and zinc oxide or white lead tinted with lampblack, for gray.
Shingle stains should not cake or change color in the container and when stirred should settle very slowly. With the exception of some dark brown stains, which are simply refined coal-tar creosote with volatile thinners, shingle stains are usually made from very finely ground pigments, drying oils, and volatile thinners. Many commercial shingle stains contain some creosote oil from coal tar or water-gas tar which is intended to act as a wood preservative. While pressure treatment with creosote is one of the most effective methods of preventing wood from rotting, the small amount that penetrates the wood from a single dip or brush treatment probably has very little effect.
Paint applied over creosote stain is likely to be ruined by the creosote bleeding through. If there is any possibility that the shingles may be painted at some future time, pigment oil shingle stains without creosote should be used.
Masonry Surfaces
Paints for masonry wall surfaces may be divided into four types: Cement water paint, resin-emulsion paint, oil paint, and paint containing rubber in the vehicle. These paints are also suitable for use on such masonry surfaces as foundations, gate posts, and fence or enclosure walls, but they should not be used on floors which are subject to abrasion. For such surfaces, a very hard-drying paint with good water resistance and gloss retention is recommended.
Cement-water paints are water-dilatable paints in which Portland cement is the binder. They are particularly suitable for application on damp, new, or open-textured masonry surfaces. These surfaces include triose walls that are damp at the time of painting, or that may become damp after painting as a result of structural defects or other causes; new structures (less than 6 months old) which normally contain water-soluble alkaline salts; and open-textured surfaces such as cinder, concrete, and lightweight aggregate block. These paints are not recommended for stopping leakage through porous walls that are exposed to water pressure, particularly if the paint is applied to the inside of the wall.
For such conditions, a coating of hot bituminous material applied to the outside of the wall is preferable.
Close-textured surfaces which are relatively dry, such as cast concrete, asbestos-cement siding, and tile, may be painted with resin-emulsion paint or paints containing rubber in the vehicle. Walls which are dry at the time of painting, and are so constructed as to remain dry after painting, may be decorated satisfactorily with oil paints.
CEMENT-WATER PAINT
Cement-water paints are water-dilatable paints, packaged in powder form. They are composed chiefly of Portland cement or Portland cement and lime and possess good decorating qualities or hiding power and color. However, when wetted, as by rain, they become somewhat translucent and darker in color. When again dry, the film returns to its original opaqueness and color.
To clean a surface for the application of cement-water paint, thoroughly remove all dust, dirt, and efflorescence, old coatings of white-wash, and flaking or scaling cement-water paint by brushing vigorously with a wire brush. Firmly adhering coatings of cement-water paint or cement-water paints which are "chalking" or "dusting" need not be removed, but should be brushed with a stiff bristle brush to make the surface uniform.
Before applying the paint, whether initially or on a previously painted surface, the masonry should be thoroughly wetted, preferably with a garden hose adjusted to produce a fine spray. A superficial dampening with a brush dipped in water is not adequate for exterior walls but may be satisfactory for cool basement walls. Usually, wetting the walls in one operation not more than an hour before painting is sufficient. The water should be applied so that each part is sprayed three or four times for about 10 seconds each, time being allowed between applications for the water to soak into the surface. If the surface dries rapidly, as it may in hot weather, it should be redampened slightly just before painting. The wall surface should be moist, not dripping wet when paint is applied.
Cement-water paint powder should be mixed with water in accordance with the manufacturer's directions. Paints may be tinted by adding suitable amounts of coloring pigments but, due to the difficulty of producing uniform colors by hand mixing, it is suggested that commercial brands of tinted paints be purchased which have been mill ground in the factory.
Cement-water paint should be applied in two coats. Preferably not less than 24 hours' drying time should be allowed between coats. The first coat should be slightly moistened with water before applying the second.
Most Portland cement paints cannot be satisfactorily applied with the ordinary hair-bristle paint brush. Proper application requires a brush with relatively short, stiff, fiber bristles such as fender brushes, ordinary scrub brushes, or roofers' brushes.
While thick films are to be avoided, there is a tendency to use too much water in cement-water paint and to brush it out too thin. Coatings applied in this manner may look well at first but will generally lose their opacity and protective value much sooner than thicker films. The proper spreading rate is difficult to estimate for Portland cement paint because of the difference in the texture of the masonry to be covered. However, on smooth masonry, 1 gallon of mixed paint should be sufficient to cover 100 sq. ft. with two coats; and, for rough masonry, 1 gallon should be sufficient to apply two coats to 50 sq. ft. of surface.
After painting, it is desirable to sprinkle the freshly painted surface two or three times a day with a fog spray, such as is used for dampening walls prior to painting, and it is recommended that this be done between coats and for 2 days after the final coat, starting as soon as the paint has set, usually 6 to 12 hours after application.
Sufficient time should be allowed between coats so that the paint film will dry hard before more paint is applied. Oil paints on exterior wood should dry at least 24 hours, several days' drying time being preferable.
Two-Coat Paint System
A minimum of three coats was formerly the accepted practice for initial painting on exterior wood, and this practice is still largely followed. However, by using special primers, two-coat paint systems for wood have been developed that are durable and satisfactory. The principle of the two-coat paint system is that as much paint is applied in two coats as normally would be applied in the three-coat method of painting. On smoothly planed wood, the usual spreading rate for three-coat painting is about 550 to 600 sq. ft. per gallon for the first or priming-coat paint and about 600 to 650 sq. ft. per gallon for each of the next two coats. In the two-coat paint system, the primer is spread at the rate of about 450 sq. ft. per gallon and the finish coat about 550 sq. ft. per gallon. Rough surfaces and weather-beaten wood require much more paint than is indicated for smoothly planed wood.
Three-Coat Paint System
Mixed-pigment prepared paints are available for three-coat work, in addition to linseed-oil white-lead paints which may be mixed on the job or purchased ready-mixed. The manufacturer's directions should be followed in thinning the first and second coats. It is sometimes advisable in moist atmospheres, particularly at the seashore, to add a small amount (1 pint to a gallon) of good exterior varnish to the top coat of paint. The varnish should first be tried in a small amount of paint to make sure that the two are compatible and that the varnish will not cause the paint to thicken.
Shingle Stains
Shingle stains are pigmented oil stains, similar to very fluid paints, which can be applied by dipping, brushing, or spraying. They are intended for application to comparatively rough exterior wood surfaces where it is not necessary to bring out the grain and texture of the wood to which they are applied, and they dry to a matt or semi-transparent finish. Durable pigments, such as iron oxides, are used for the colors red through brown; chromium oxide, for green; and zinc oxide or white lead tinted with lampblack, for gray.
Shingle stains should not cake or change color in the container and when stirred should settle very slowly. With the exception of some dark brown stains, which are simply refined coal-tar creosote with volatile thinners, shingle stains are usually made from very finely ground pigments, drying oils, and volatile thinners. Many commercial shingle stains contain some creosote oil from coal tar or water-gas tar which is intended to act as a wood preservative. While pressure treatment with creosote is one of the most effective methods of preventing wood from rotting, the small amount that penetrates the wood from a single dip or brush treatment probably has very little effect.
Paint applied over creosote stain is likely to be ruined by the creosote bleeding through. If there is any possibility that the shingles may be painted at some future time, pigment oil shingle stains without creosote should be used.
Masonry Surfaces
Paints for masonry wall surfaces may be divided into four types: Cement water paint, resin-emulsion paint, oil paint, and paint containing rubber in the vehicle. These paints are also suitable for use on such masonry surfaces as foundations, gate posts, and fence or enclosure walls, but they should not be used on floors which are subject to abrasion. For such surfaces, a very hard-drying paint with good water resistance and gloss retention is recommended.
Cement-water paints are water-dilatable paints in which Portland cement is the binder. They are particularly suitable for application on damp, new, or open-textured masonry surfaces. These surfaces include triose walls that are damp at the time of painting, or that may become damp after painting as a result of structural defects or other causes; new structures (less than 6 months old) which normally contain water-soluble alkaline salts; and open-textured surfaces such as cinder, concrete, and lightweight aggregate block. These paints are not recommended for stopping leakage through porous walls that are exposed to water pressure, particularly if the paint is applied to the inside of the wall.
For such conditions, a coating of hot bituminous material applied to the outside of the wall is preferable.
Close-textured surfaces which are relatively dry, such as cast concrete, asbestos-cement siding, and tile, may be painted with resin-emulsion paint or paints containing rubber in the vehicle. Walls which are dry at the time of painting, and are so constructed as to remain dry after painting, may be decorated satisfactorily with oil paints.
CEMENT-WATER PAINT
Cement-water paints are water-dilatable paints, packaged in powder form. They are composed chiefly of Portland cement or Portland cement and lime and possess good decorating qualities or hiding power and color. However, when wetted, as by rain, they become somewhat translucent and darker in color. When again dry, the film returns to its original opaqueness and color.
To clean a surface for the application of cement-water paint, thoroughly remove all dust, dirt, and efflorescence, old coatings of white-wash, and flaking or scaling cement-water paint by brushing vigorously with a wire brush. Firmly adhering coatings of cement-water paint or cement-water paints which are "chalking" or "dusting" need not be removed, but should be brushed with a stiff bristle brush to make the surface uniform.
Before applying the paint, whether initially or on a previously painted surface, the masonry should be thoroughly wetted, preferably with a garden hose adjusted to produce a fine spray. A superficial dampening with a brush dipped in water is not adequate for exterior walls but may be satisfactory for cool basement walls. Usually, wetting the walls in one operation not more than an hour before painting is sufficient. The water should be applied so that each part is sprayed three or four times for about 10 seconds each, time being allowed between applications for the water to soak into the surface. If the surface dries rapidly, as it may in hot weather, it should be redampened slightly just before painting. The wall surface should be moist, not dripping wet when paint is applied.
Cement-water paint powder should be mixed with water in accordance with the manufacturer's directions. Paints may be tinted by adding suitable amounts of coloring pigments but, due to the difficulty of producing uniform colors by hand mixing, it is suggested that commercial brands of tinted paints be purchased which have been mill ground in the factory.
Cement-water paint should be applied in two coats. Preferably not less than 24 hours' drying time should be allowed between coats. The first coat should be slightly moistened with water before applying the second.
Most Portland cement paints cannot be satisfactorily applied with the ordinary hair-bristle paint brush. Proper application requires a brush with relatively short, stiff, fiber bristles such as fender brushes, ordinary scrub brushes, or roofers' brushes.
While thick films are to be avoided, there is a tendency to use too much water in cement-water paint and to brush it out too thin. Coatings applied in this manner may look well at first but will generally lose their opacity and protective value much sooner than thicker films. The proper spreading rate is difficult to estimate for Portland cement paint because of the difference in the texture of the masonry to be covered. However, on smooth masonry, 1 gallon of mixed paint should be sufficient to cover 100 sq. ft. with two coats; and, for rough masonry, 1 gallon should be sufficient to apply two coats to 50 sq. ft. of surface.
After painting, it is desirable to sprinkle the freshly painted surface two or three times a day with a fog spray, such as is used for dampening walls prior to painting, and it is recommended that this be done between coats and for 2 days after the final coat, starting as soon as the paint has set, usually 6 to 12 hours after application.
Source...