Lesson 2-4 SELECTING EXTERIOR AND INTERIOR PROTECTIVE COATINGS

2-10.  Exterior Protective Coatings

You must consider the type of surface when selecting a protective coating for a particular job.

     a.  Types of Surfaces.

         (1)  Wood. When exterior wood surfaces are painted, you must decide whether the two-coat or three-coat system is to be used. Primer is not necessary when you repaint previously painted surfaces that are in good condition. For surfaces that have never been painted, use a primer coat, a body coat (undercoat), and a final (finish) coat. Alkyd-modified, oil-based paints and latex, water-based, exterior white paints (house paint) have replaced white oil-based paints. If a primer is required, use the type recommended by the manufacturer of the final coat of paint.

         (2)  Metal. Metal surfaces, such as galvanized iron, tin, and steel building materials, require protective coatings. Metal surfaces may rust if they are not protected against moisture. Copper does not rust, but it gives off a corrosive wash that discolors the metal. Aluminum does not rust, but it corrodes if it is unprotected. After applying the proper primer coat, apply conventional house paints (alkyd) or exterior latex to metal surfaces (other than copper). With the exception of metal roofing and copper, you may also use aluminum paint to paint metal surfaces.

         (3)  Masonry. A variety of paint products is available to coat masonry surfaces, such as brick, cement, stucco, cinder block, or asbestos cement. One of the newer ideas for painting brick is a clear coating that withstands weather, yet allows the natural appearance of the surface to show through. You may also use cement-based paints, rubber-based coatings, and vinyl and alkyd paints on many types of masonry. You may apply almost all exterior house paints to masonry; however, you must prepare the surface properly. Good results are obtained by painting concrete porches and steps with a rubber-based coating or similar product. Roughening the surface slightly with muriatic acid is recommended before painting concrete that is hard and glossy. All concrete surfaces must be primed with an alkali-resistant primer.

     b.  Types of Exterior Coatings. Several of the most commonly used coatings for exterior surfaces are listed below. Notice that some are applied on exterior and interior surfaces. New paints are being developed each year, so you should read the latest literature and technical publications to keep abreast of new developments.

         (1)  White alkyd, latex, and acrylic paint. Alkyd paint is a glossy enamel that is compounded for use as a second or final coat on exterior wood or metal and on interior drywall or plaster. It offers heavy-duty protection for these surfaces. Alkyd paint also comes in a flat finish. Flat-latex and satin-gloss acrylic paints are formulated for most exterior building surfaces of wood, metal, and masonry. Most latex paints may be thinned slightly with water for spray application. For success with these paints, always use an alkyd or latex exterior primer. Some latex paints are self-priming if they are painted over previously painted wood surfaces that are in good condition.

         (2)  Masonry white latex (acrylic) paint. This paint is intended for exterior body or final coats on primed masonry surfaces (except floors). The paint, white or tinted, dries to a flat finish; so when a glossy finish is desired, you must use exterior glossy paints. Paint adheres poorly to glazed surfaces, so you must roughen such surfaces by acid-washing, sandblasting, or rubbing the glaze off with abrasive stones. It is unnecessary to remove old coatings, organic compounds, or cement-water paints that are firm. However, you must remove paint that is loose or flaking to ensure adhesion of the new paint. Since moisture is detrimental to exterior masonry paint, surfaces must be thoroughly dry before primer, body, and final coats are applied.

         (3)  Zinc-oxide oil or resin paint. A zinc-dust and zinc-oxide paint is manufactured to prime zinc surfaces. You may also use the paint for body and final coats. There are several types of this zinc primer. One type is an air-drying paint that has a linseed-oil vehicle. Another type, an enamel, has a glycerol-phthalate vehicle that causes the paint to dry faster. This enamel can be baked dry if necessary. Still another type, an enamel containing phenolic resin, is recommended for priming the inside surfaces of steel water tanks because the primer is nonpoisonous. Before using zinc primer on new surfaces, you must clean the surfaces with turpentine, mineral spirits, or another approved cleaner to ensure good adherence of the primer coat.

         (4)  Olive-drab oil-based paint. This exterior paint is suitable for use on wood, metal, and masonry that is exposed to the elements. It is a semigloss paint that has good color retention, and it is used for body and final coats.

         (5)  International-orange oil-based paint. This paint consists of two different types of paint, and it comes in two colors-chrome orange (color of a ripe tomato) and orange red. The most durable type of international-orange paint is chrome-orange-pigmented, linseed-oil paint. It is a slow-drying paint used for body and final coats on exterior surfaces of large buildings. A small amount of spar varnish is included in the paint to retain color; however, the color still has a tendency to fade due to exposure.

International-orange enamel is the other type of international-orange paint and is similar in color to the above paint. It is not as durable; however, it holds its color much better and dries faster. The vehicle in the enamel is glycerol-phthalate synthetic enamel. The enamel is a vivid orange red, and it is very durable. The color is fast, and it looks best when applied over body coats of the same color. The enamel dries enough overnight to allow sanding and application of another coat. The enamel is recommended for body and final coats on small, metal surfaces.

         (6)  Chrome-yellow oil-based paint. This exterior paint is a durable, bright yellow paint that is applied as a final coat on wood, metal, and masonry. Use it primarily for painting towers and traffic signs. Significant names applied to tints of this paint are Highway-Marking Yellow, Army-Navy Aircraft Yellow, and War-Department Yellow.

         (7)  Rust-inhibiting, solvent-resistant drum enamel. This exterior enamel is used for coating metal drums and is an olive-drab, semigloss enamel. It is a one-coat enamel that contains glycerol-phthalate resin, and it dries fast.

         (8)  Aluminum-paint mixing varnish. A mixing varnish is contained in aluminum paint that is used for priming exterior wood and for general purposes. You may also use it for final coats on metal. Tung-oil varnish is used as the vehicle in aluminum paint for general use. Tung-oil varnish is one of two types of mixing varnish. If it is necessary to spray paint, 1 gallon of aluminum paint containing mixing varnish may be thinned with 1 pint of turpentine. In order to bring paint to the proper consistency, add aluminum paste when using mixing varnish of high viscosity and add aluminum powder when using mixing varnish of low viscosity.

         (9)  Asphalt varnish. This varnish is a general-purpose varnish that is used when covering water pipes, gas pipes, and so on. It is composed of asphalt mixed with drying oils, solvents, and driers. When dry, asphalt varnish has a smooth, glossy finish that is similar to glossy, black enamel.

         (10)  Water-resisting spar varnish. This is a durable covering for interior or exterior use. When dried, it has a softer film and less luster than some of the other oil-type varnishes.

         (11)  Clear and pigmented spraying lacquer. A spraying lacquer is either clear or pigmented. It is used over suitably primed metal and wood interior and exterior surfaces. For repaint jobs, apply a sealer or bleeder coat before the lacquer is sprayed over a color. Ordinarily, the spraying lacquer does not require thinning.

         (12)  Cold-water white paint powder and liquid. Exterior cold-water paint powder makes an inexpensive paint that dries to a porous film. It is breathing paint that is used on masonry surfaces where permeability and durability are important. The paint is also available in colors. You may often mix linseed oil and spar varnish with water to form the vehicle for exterior cold-water paint and to make the paint more durable; however, special water-dispersible oils are on the market which effect better dispersal of the oil throughout the water. The paints resulting from either vehicle are equal in quality. Cold-water paint is applied to clean, masonry surfaces, such as concrete, brick, wet walls, and so forth. Masonry surfaces should be uniformly dampened (not wet) before the paint is applied. You may also use the paint on clean, primed wood or metal surfaces.

         (13)  Black oil-based paint. This paint is a glossy, slow-drying paint that is used for final coats on the surfaces of exterior wood, masonry, and structural steel. It is durable and has excellent hiding qualities when used on structural steel that has been primed and body-coated with two coats of rust-resistant paint.

         (14)  Black-graphite oil-based paint. This paint is used as body and final coats to cover primed surfaces of ferrous metals. The graphite in the paint has leafing properties that account for its durability. There are two types of graphite paint. One type is a steel-gray paint that has a metallic luster. Lampblack or carbon black is mixed with natural flake graphite, as well as other types of natural and artificial graphites, and is dark in color. Light-colored graphite paint is intended for body coats, and dark-colored graphite paint is designed for final coats.

         (15)  Iron-oxide red and brown oil-based paint. Exterior iron-oxide paint is manufactured in different colors of red and brown. It is an economical paint, and it is durable. Spar varnish and zinc oxide in the paint increase its color retention and decrease the paint's tendency to mildew. Iron-oxide paint is intended for use on roofs, barns, freight cars, and so forth. It may be used for body and final coats on metal, wood, and masonry. You can use this paint as a primer on structural steel, although it is not as satisfactory as a rust-resistant agent for ferrous metals.

         (16)  Aluminum. Aluminum paint is probably used for more jobs than any other paint. It is a desirable coating for battleships and large bridges, since the dried film weighs less than half as much as the film of any other common paint. It is used to cover and protect steel structures and buildings, because it is durable and light-colored. It reflects light and heat more than any other paint and has a desirable decorative finish. It is commonly used as a body and final application over a red iron-oxide, zinc-oxide, or linseed-oil priming coat.

Aluminum paint provides excellent service when applied in two or three coats, without priming paint, to clean and rust-free surfaces. When you paint steel, the importance of clean surfaces cannot be overemphasized. Aluminum paint is also used successfully for painting galvanized iron. Without a primer, the paint will bond satisfactorily with the galvanization if the metal has been exposed to the weather for at least 6 months. Aluminum paint possesses excellent durability when used as a priming coat for wood construction. It will cover soft, pitchy, and resinous spots very effectively. It also prevents the bleeding of wood stains. You may apply final coats of light-colored paint when the correct aluminum paint is used as an undercoat.

         (17)  Cement-based paint. This paint comes in powder form and is used on porous interior and exterior masonry surfaces (except gypsum plaster). There are two types of powder. One type has 80 percent portland cement and 10 percent hydrated lime. The second type has more hydrated lime and less portland cement than the first. Use the first type for painting inside surfaces of swimming pools, water tanks, and so forth. Both types contain small percentages of titanium dioxide, zinc sulfate, water repellents, and calcium or aluminum stearate.

         (18)  Plastic paint. Plastic paint is another type of protective coating available on the market in recent years. The word plastic, as applied to paints, is an abused term. The fact that this word or some variation of it appears in a trade name does not necessarily mean the product has extraordinary properties. Any synthetic resin paint might be called plastic paint because the phenolic, vinyl, and other synthetic resins commonly used in paints are varieties of plastic, compounded with special grades of solution-type resins. True plastic coatings are now available, and some of the common ones are discussed below. These are tough, flexible coatings that are highly resistant to the natural elements and many chemicals. They are especially suitable on surfaces where most other coatings have been ineffective. With increased use and improved application methods, costs of plastic coatings are expected to decrease.

              (a)  Vinyl-resin plastics. Vinyl-resin plastics are being used as protective coatings. They include plastisols, organosols, and dry (generally powdered) vinyl resins. Plastisols are vinyl resins that are dissolved in liquid plasticizers, which remain chemically unchanged until heat-treated. Organosols are similar to plastisols, except small amounts of volatile solvents are added to improve the application properties. Both have a high solid content; and the plastisols are essentially 100 percent solids. The fusion of resins and plasticizers to form plastic film is caused by raising the temperature of the film between 300 and 360F. These plastics are used to manufacture such items as dishwasher racks, dish drainers, plating tanks and racks, piping and vinyl-on-metal laminates for luggage, instrument cabinets, and furniture. Other plastics, such as cellulosic, acrylonitrile, and acrylic are being used as protective coatings. These are generally applied by heat processes when the dry resin is fused onto the surface to be protected. They are applied as temporary coatings to gears, shafts, screws, and other machine parts during shipment and storage.

              (b)  Plastic tapes. Plastic tapes are being used to protect steel pipe. Self-adhering plastic tapes and those requiring a primer are available. Polyethylene and polyvinyl-chloride tapes are the most common ones and are available in 10-, 12-, and 20-mil thickness (20 mils is 20 thousandths of an inch). You will generally use a wire brush to clean the surface, and a primer may be needed before you apply the tape.

         (19)  Floor and deck enamel. A paint with a varnish vehicle is, in reality, an enamel. It is intended for body and final coats on primed wood and concrete surfaces. It is an excellent, fast-drying, tough covering that is flexible enough to withstand wear and weather. To make self-primer for

         (20)  Bituminous (coal tar) or asphalt coating. This coating is used extensively as waterproofing, as roofing, and for protection of submerged and buried metal pipes and devices. It is applied at reasonable cost and makes a substantial barrier against attack by moisture and oxygen. Asphalt coating is available as an enamel, a cold-applied paint, and an emulsion. It is considered more resistant to the elements than coal tar.

         (21)  Waterproofing paint. Masonry is porous and soaks up water, causing damp interior walls, cracked plaster, and peeling wallpaper and paints. Silicone water-repellent paint will usually prevent this problem. With a single application (spray or brush), you will be able to provide an invisible water-repellent surface that will preserve the finish for 5 to 10 years. Oil-based and cement-based paints can be applied over the application. Oil-based paints will destroy the breathing characteristics of the masonry.

         (22)  Swimming-pool paint. Rubber-based paint is popular for painting swimming pools and other water-holding structures; however, water-mix cement-based and enamel paints with a water-resisting varnish vehicle of synthetic resin are popular. Recent developments have led to the use of epoxies, polyesters, and urethanes that have better resistance to water, chemicals, and abrasion than conventional coatings; but they are more expensive.

         (23)  Fungicidal paint. Fungicidal paint is used to preserve wood and fabrics by preventing rot. These paints are popular for foundation timbers, sills, fence posts, and farm buildings.

         (24)  Fire-retardant paint. Fire-retardant paint retards the spread of fire by a chemical action of the contents that tends to smother the fire.

         (25)  Camouflage paint. Camouflage paint has a dull finish, does not fade, is easily applied, is inexpensive, and covers in one coat. Camouflage paint is available in nine colors: light green, dark green, sand, field drab, earth brown, earth yellow, loam, earth red, and olive drab.

         (26)  Traffic paint. A ready-mixed traffic paint is known as centerline, zone-marking, and road-marking paint. It is available in white and yellow, and it is intended for application at a wide range of temperatures to bituminous and concrete highways bearing heavy traffic. Another type of traffic paint is one in which glass spheres are added when the paint is applied to the road surface. This semipaste form of paint, available in various colors, is called a pigmented binder. The glass beads serve as reflectors when automobile lights strike them at night.

         (27)  Whitewash. Whitewash is a lime paste mixed with water. The paint is inexpensive and used for covering interior and exterior wood or masonry surfaces. You primarily use it on brick, concrete, road or roadside obstructions (sidewalks, parking curbs, light posts), sheds, telephone poles, and so forth Make lime paste by slaking quicklime in enough water to make a stiff paste and allowing it to cure for several months. The mixing ratios for two good lime pastes are: 20 pounds of quicklime to 10 gallons of water, and 50 pounds of hydrated lime to 6 gallons of water.

Two formulas for compounding whitewash are shown in Table 2-4. Notice that both formulas start out with the same weight of lime paste; however, the remaining materials and weights are different.

Table 2-4. Whitewash formulas

Material Formula Number 1 Formula Number 2
Casein 5 pounds  
Trisodium phosphate 3 pounds  
Line paste 8 gallons 8 gallons
Water 6 gallons 4 gallons
Common salt   12 gallons
Powdered alum   6 ounces
Molasses   1 quart

C. Recommended Exterior Coatings.

Table 2-5, is a guide showing the type of coating recommended for various exterior surfaces. This chart is designed for general applications, and many times, variations must be made. The color selected for exterior surfaces should blend with other structures in the area. Color selection at an installation is often made by personnel other than protective-coating specialists.

Table 2-5. Recommended exterior coatings

Surfaces House Paint
(Alkyd)
Transparent
Sealer
Cement-Based
Paint
Aluminum
Paint
Wood
Stain
Roof
Coating
Roof
Cement
Asphalt
Emulsion
Trim and Trellis Paint Awning Emulsion Spar Varnish Porch and Deck Paint Primer or Under-coating Metal
Primer
Latex Paint
Clapboard siding                      
Bricks                  
Cement and cinder blocks                  
Asbestos cements                        
Stuccos                  
Natural wood siding and trims                          
Metal siding                    
Wood-frame windows                    
Steel windows                    
Aluminum windows                    
Shutters and other trims                      
Canvas awning                            
Wood-shingle roofs                            
Metal roofs                        
Coal-tar felt roofs                        
Wood porch floors                            
Cement porch floors                          
Copper surfaces                            
Galvanized surfaces                  
Iron surfaces                    
 

Legend:

= A primer or sealer is unnecessary before before the finishing coat is applied.
= A primer or sealer may be necessary before the finishing coat is applied (unless the surface has been previously finished.)

2-11.  Interior Protective Coatings

There are many types of interior coatings available. These coatings are decorative and designed for use on certain types of surfaces.

     a.  Types of Surfaces.

         (1)  Wood. Alkyd paints for interior wood surfaces comes in flat, semigloss, and gloss paint finishes. Some paints come in tints as well as white. Alkyd enamels have a good hiding quality and flow smoothly. They offer durable to heavy-duty protection for wood, metal, drywall, and plaster. Latex paint is washable, and the finish may be gloss, semigloss, or flat. Some latex paints come in tints as well as white, and the tinted paints have a low-luster finish.

For interior woodwork that is to have a natural finish, you should prime and seal it with a ready-mixed varnish or spraying lacquer that is diluted with the recommended thinner. The varnish or lacquer is applied after the drying oil and filler have been put on and are dry enough to receive the primer-sealer. When interior woodwork is stained, shellac varnish is used as a primer-sealer to avoid the bleeding of aniline (synthetic organic dye) stains. You may use varnish or lacquer as a primer-sealer on other types of stains.

         (2)  Metal. When you paint interior metal surfaces, you should use a primer, at least one body coat, and a final coat. If more coats are applied, the additional coats are called body coats.

         (3)  Masonry. Interior masonry surfaces may be body-coated and final-coated with alkyd enamel or polyurethane paint that is used on wood or metal surfaces. Final coats are selected based on the color and the type of finish desired. For high-traffic areas, latex-based paints that will give a flat or an eggshell finish are available. When you desire a gloss or semigloss finish, you will generally resort to other alkyd enamels or latex paints.

     b.  Types of Coatings. Several of the most commonly used coatings for interior surfaces are listed below. Notice that some are used on exterior surfaces and interior surfaces. New paints are being developed all the time, and you should read current publications that deal with protective coatings.

         (1)  Interior cold-water white paint. This white paint comes in powdered form and is mixed with cold water. The paint is available in white and tints. This paint is primarily intended to cover primed, wet (damp) walls and other masonry surfaces. It is not satisfactory for surfaces that are continually damp because of its susceptibility to mildew. When repainting surfaces, you must remove calcimine and loose or powdering oil-paint coatings.

         (2)  Primer-sealer floor lacquer. This lacquer is intended for sealing clean, wooden floors that have been sanded. By sealing a newly sanded, close-grained or open-grained floor, you help fill the wood pores and provide a good foundation (priming coat). The primer-sealer reduces the tendency of the finished surface to mar, integrates the filler and the wood, and smoothes the surface.

         (3)  Fume- and heat-resistant white enamel. This enamel is used in chemical laboratories, dairies, refrigerator rooms, sewage-disposal plants, and areas subjected to temperature or fumes. To avoid discoloration, the paint must be free from lead and iron. This enamel consists mostly of light-proof lithopone, titanium, zinc oxide, or a mixture of these pigments. The vehicle must exclude any metallic-compound driers but should include linseed, tung, soya, or other drying oils, along with damar, resin, and turpentine or mineral spirits. Use a softener, such as pine oil, to plasticize the paint. Fume- and heat-resistant white enamel will stand some tinting, particularly light gray, without discoloring under adverse conditions. The enamel is not as flexible as other white enamels and is less water-resistant than some of the quick-drying enamels.

         (4)  Flat white alkyd or latex enamel. This interior enamel is odorless and comes in tints as well as white. Latex flat wall paint is washable and may be applied to prepared walls and ceilings, wood trim, wallboard, primed plaster, brick, and masonry. Latex flat paint comes in white and eggshell.

         (5)  Semigloss white alkyd or latex enamel. This interior enamel may be used when a tough, durable, washable finish is needed (without the shine of gloss). The enamel also comes in a variety of tints.

         (6)  Gloss white alkyd or latex enamel. This enamel paint may be used on almost any interior wood, metal, drywall, or plaster surface.

         (7)  Polyurethane enamel white paint base. This interior paint base comes in white or tinted enamel. Polyurethane enamel is a water-based formula intended for making paints to be used on interior wet or dry walls, woodwork, trim, house and deck furniture, cabinets, and crafts. Polyurethane enamel is lead-free, solvent-free, nonflammable, has low odor, and dries to touch in 30 minutes. Use the paint on suitably primed wood and metal surfaces. The object to be body- and final-coated with resin-emulsion paint must be clean; and in case of a repaint job, the old paint must be firm or be removed from the surface. The paint is an oil-in-water emulsion product. Although you can apply it by any convenient painting method, it can be thinned only with water. The paint dries sufficiently hard overnight to be recoated. Directions for mixing with water are often placed on the container, and you should follow them.

         (8)  Concrete-floor, rubber-based paint. A rubber-based paint is made for use on interior concrete floors that are subjected to dampness and not exposed to sunlight. When used as a primer coat, you should mix 1 pint of mineral spirits and 1 pint of toluol (commercial grade) with 1 gallon of paint. You apply body and final coats as furnished in the container.

         (9)  Cold-water white paint. This interior paint comes in tints as well as white. It is intended primarily for covering primed wet wall and other masonry surfaces. It is not satisfactory for surfaces that are continually damp because of its susceptibility to mildew. You must remove calcimine and loose or powdering oil-paint coatings from surfaces being repainted.

         (10)  Heat-resistant black enamel. This enamel is manufactured for use on steam pipes and boiler fronts where temperatures of 400F or higher are common. The objects you paint should be cooled below 140F before paint is applied, and they should be held at this temperature for at least 48 hours before being subjected to a higher temperature. Painting with enamel indoors is dangerous, so paint in well-ventilated areas and away from lights or flames. There are two types of heat-resistant black enamel for metal. One type has a bituminous base that is otherwise unpigmented. The other type has a resin base and is pigmented; it is also gasoline- and water-resistant.

         (11)  Luminous paint. Luminous paint is used to make areas glow with a brilliance. In dangerous areas throughout a building, it will act as a safety guide and show danger areas even after the lights are out. It is similar to the dial and hands on a luminous watch.

         (12)  Wax. Wax is available in paste, emulsion, and liquid. It is an important part of the finishing process, especially on furniture and floors. Wax is normally applied over varnish or shellac to protect the coated surface. You often apply it directly over sealer to provide a waterproof coating.

         (13)  Linseed oil. Linseed oil, as previously explained in this lesson, may also be used as a finish for wood surfaces. You ordinarily apply it by rubbing.

         (14)  Spirit varnish. Spirit varnish is a substitute for shellac varnish and may be used on interior wood, metal, paper, and fabric surfaces. You may substitute it for oil varnishes where rapid drying is more important than durability. This varnish is almost equivalent to shellac varnish, and you can brush or spray it on. It cannot be satisfactorily mixed with oil-based paints, oil varnishes, lacquers, turpentine, or mineral spirits.

         (15)  Shellac varnish. Shellac varnish is used primarily as a sealer and primer for interior wood and masonry surfaces. Although it is not as durable in some ways as oil varnishes, some painters use it for body and final coats. Occasionally, you will use it on exterior wood surfaces that are not directly exposed to the weather.

Shellac varnish is either white (bleached) or orange and is available in light-, medium-, and heavy-bodied consistencies. Shellac varnish comes in two grades. One grade is light in color and is practically free of resin and suspended matter. The other grade is dark in color and contains some insoluble matter; therefore, this shellac varnish is used where darker color and some resin are not objectionable. One thinner for shellac varnish consists of 5 parts methyl alcohol to 100 parts ethyl alcohol. Another thinner consists of 1 part aviation gasoline, 5 parts denatured ethyl acetate, and 100 parts denatured alcohol.

         (16)  Orange shellac. Orange shellac is used to make shellac varnish. Several grades of orange shellac are on the open market. The highest grades are known as superfine and other names. The second highest grade is resin-free and darker than the higher grades. The lowest commercial grade contains some resin. This grade is darker in color than the two highest grades.

         (17)  Damar varnish. Damar varnish is a spirit made to use as a final coat on interior surfaces. It is also used by manufacturers as a vehicle for some white and tinted enamels used for covering interior metal surfaces, such as radiators, that are exposed to high temperatures. It is not satisfactory for surfaces exposed to moisture and abrasion.

         (18)  Primer-sealer floor varnish. This varnish is used for treating wood and cork floors. It furnishes a good foundation for wax and other coats of varnish, and it helps fill open-grained wood. There are two classes of this varnish. One class is made for use on close-grained woods, and the other is made for use on open-grained, filled woods. Primer-sealer floor varnish is actually spar varnish that is thinned with turpentine or mineral spirits. When cut with thinner equal to one-half its volume, the mixture is similar to the class of primer-sealer varnish made for open-grained wood. When cut with equal amounts of thinner, the mixture is about the same consistency as the primer-sealer varnish made for close-grained woods.

         (19)  Interior varnish. Interior varnish is manufactured to use on inside woodwork and floors, except where the varnish is required to have rubbing qualities.

         (20)  Interior cabinet rubbing varnish. This varnish is intended for use on interior wood surfaces where a rubbed finish is desired. It is not a baking varnish for metal, nor is it a suitable varnish for floors.

     c.  Recommended Interior Coatings.

Table 2-6, is a guide showing the type of coating recommended for various interior surfaces. This chart is designed for general applications, and many times, variations must be made. It is always wise to read the label on the container to ensure that the coating is compatible with the surface and primer being used.

Table 2-6. Recommended interior coatings