RESIN-EMULSION PAINT
Resin-emulsion paints are water-thinned materials whose dry-film properties closely resemble those of a flat oil paint. They may be used on most porous masonry surfaces, including asbestos-cement siding, which has not been previously coated with a waterproofing compound. They should not be used on magnetite stucco.
To prepare the surface for resin- emulsion paints, remove by brushing or washing all dust, dirt, efflorescence, and loose particles from the surface; and also remove any flaking or scaling paint by scraping or wire brushing. Glossy areas should be dulled by sanding; oil, grease, and wax should be removed by scrubbing with mineral spirits. Then wash with water containing trisodium phosphate (about 2 ounces to the gallon), and rinse thoroughly with clean water.
Resin-emulsion paints are packaged in paste form and need to be thinned with water before being applied. They should be mixed in clean metal containers (not wood) in accordance with the directions given on the manufacturer's label and not allowed to stand after mixing for more than a week.
Resin-emulsion paint should be applied in two coats and the air temperature when painting should be above 50° F. A sizing or priming coat is not generally required except on open-textured masonry. For that, a cement-water paint containing sand should be used to fill the voids in the wall surface. On very warm days, it may be advisable to moisten the surface to be painted with water, prior to applying the paint. Resin-emulsion paint will dry in 1 to 4 hours, and may be recoated in 6 to 8 hours; the film becomes hard overnight. One gallon of the paste paint will cover approximately 200 to 450 sq. ft., depending upon the surface and the application. Brushes and spray guns should be washed with warm soapy water immediately after using.
OIL PAINTS
Oil paints intended for use on masonry are usually ready-mixed paints containing weather-resistant opaque pigments suspended in drying oils, resins, and thinners. They should be formulated so that the first coat seals the surface sufficiently to prevent spots or flashes of the second coat. Two coats are necessary for good hiding and durability.
Moisture back of the paint film will seriously impair the life of a coating of oil-base paint, therefore the application of oil paint to new masonry should be deferred until the walls have had time to dry. This may require 3 months to a year, depending upon the thickness and porosity of the wall and the weather conditions. Because of the importance of preventing water from entering the walls after painting, repairs of structural defects, such as leaks around flashing, doors, and windows, should be made before applying oil-base paint.
Dust and dirt should be washed off and efflorescence should be brushed off with a stiff fiber or wire brush. All traces of oil should be removed with steel brushes, abrasive stones, or a lye solution. However, if the surface is badly stained, it should be lightly sandblasted.
Caution: - When using lye (caustic soda, sodium hydroxide), avoid splashing the eyes, skin, and clothing because it may cause burns.
Old coatings of organic paint or cement-base water paint in sound condition need not be removed. Whitewash or peeling, scaling, or flaking paints should be completely removed.
Oil paints should not be applied during damp or humid weather or when the temperature is below 50° F. At least 1 week of clear dry weather should precede the application of the first coat. As masonry surfaces tend to chill and collect condensed moisture, painting early in the morning and late afternoon should be avoided except in dry climates.
A minimum of 90 days' drying time should elapse before applying oil paint over a cement-water base or over mortar-filled joints and cracks. When it is not practicable to wait this long before painting, a calking compound rather than cement mortar should be used as a crack filler.
RUBBER-BASE PAINTS
There are two types of rubber-base paints, the rubber-solution and rubber-emulsion types.
Rubber-solution paints are available at most paint stores and usually sell for slightly more than oil- base masonry paints. They may be applied by brush, spray or roller to dry or slightly damp walls. They are suitable for painting asbestos-cement siding and shingles. These paints are also useful for "sealing in"' stains on old masonry, and as protective primers under finishing coats of resin-emulsion or oil-base paints.
The same procedure outlined for preparing the surface for oil-base paints should be followed for rubber-base paints in removing dust, dirt, loose mortar, form oil, and efflorescence on dense surfaces.
Oil paint coatings must be removed before applying rubber-solution paints because the thinners used in these paints act as solvents for the oil paints. This is not necessary when applying rubber-emulsion paints over oil paints that are in good condition since they do not contain solvents that will soften the oil paints.
Rubber-base paints may be applied to dry or damp walls. It is usually necessary to thin the paint for the first coat, using the thinner recommended by the manufacturer, as some paint thinners are incompatible with rubber-base paints. The paint dries to the touch within three hours but, at least 18 hours' drying time should be allowed between coats, otherwise the succeeding coat will "lift" or soften the undercoat.
The brushing technique for rubber-base paints is the same as for applying enamels. "Back-brushing" or "working" the paint will cause it to roll and pull under the brush. As the paint tends to "set" rather quickly, it is advisable to work in shade rather than sunlight.
Brushes and spray guns should be cleaned with paint thinner immediately after they are used, because dry paint is difficult to redissolve once it has hardened.
Iron and Steel Surfaces
The chief reason for applying paint to exterior metalwork, particularly iron and steel, is to control and prevent corrosion. For best results two coats of priming paint followed by two coats of top or finishing paint are recommended on new work. For repainting, a spot coat followed by a full priming coat, and then one or two finish coats are recommended. The usual recommended spreading rate of each coat of paint is about 600 sq. ft. per gallon. It should be stressed that the preparation of the surface, particularly steel, prior to painting is important, for unless the surface is properly cleaned so that the priming paint comes in direct contact with the metal, early failure of the paint film will probably occur.
Cleaning is the most important step in preparing metalwork for painting. It can be divided into two phases; the removal of oil and grease, and the removal of rust, dirt, scale, old paint, and moisture. All oil and grease should be removed before using mechanical methods of cleaning. The usual method is to wipe the surface with clean cloths and mineral spirits or carbon tetra-chloride. The liquid as well as the cloths should be kept clean by frequent renewals to avoid leaving a thin, greasy film on the surface. When the oil and grease have been disposed of rust, scale, and old paint may be cleaned from the surface with wire brushes, steel wool, or motor-driven rotary brushes.
Since the main function of a priming coat is to protect metal from corrosion, it should contain rust-inhibitive pigments. It can be applied by either brush or spray but particular care should be taken to cover the surface completely with the proper thickness of paint. Two coats of primer are recommended for new work. The second coat may be tinted to a slightly different color to make sure of adequate surface coverage. Ample time should be allowed for drying before application of succeeding coats.
Two practical coatings for steel surfaces are red-lead and iron oxide paints, red lead being used as a primer and iron oxide as a finishing material. Dull red and brown iron-oxide paints are economical for painting terneplate roofs and structural metal. They are durable and are frequently referred to as roof and barn paint.
Red lead is available in three types: Type I, red-lead linseed oil paint which should be allowed to dry for a week between coats; type II, semi-quick-drying red-lead paint which is an easy brushing material suitable for general use and dries in 24 hours; and type III, red-lead paint in a varnish vehicle which dries within 8 hours and may be used for touch-up work on clean smooth steel.
Zinc-dust primers have good rust-inhibitive properties and are particularly effective for galvanized iron and sheet zinc. While the primary function of these paints is to provide adequate adherence on galvanized metal, they are also satisfactory as finish paints and may be used in one or more coats.
Quick-drying metal primers for home workshop machinery and automobiles are iron-oxide primers in which the vehicle is a thin varnish. They dry to a smooth velvety, flat eggshell finish, and give excellent foundations for decorative coats.
As finish coats on iron or steel, black and dark-colored paints are more durable than light-tinted paints. Red-lead paint should not be used as a final coat, since it does not retain its color. One of the best finish coats for metal is aluminum paint made by mixing about 2 lbs. of aluminum powder or paste with 1 gallon of spar varnish.
Copper
Copper gutters and flashings, as well as copper or bronze screening, may cause yellowish-green stains on light-or white-painted houses. One way to avoid this is to paint or varnish the copper or bronze. The surface of the metal should be cleaned by washing with gasoline or turpentine, and a priming coat composed of 3/2 to 2 lbs. of aluminum powder to 1 gallon of aluminum mixing varnish applied, followed by the desired color coat. Weathered copper or bronze fly-screening should be dusted and then given two coats of thin black enamel. Zinc dust-zinc oxide paints may also be used on copper and bronze if a gray color is acceptable.
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