Your job is to apply protective coatings to buildings and other structures. It is necessary that you know how to select the best methods and equipment to do a satisfactory job faster, safer, and the most economical for the military. To avoid duplication, equipment that is used for surface preparation and application is covered in only one of the categories.

3-3.  Paint-Preparation Tools

The basic tools to assist with protective-coating preparations and applications are hand paddles, power mixers and shakers, paint buckets, and paint strainers.

     a.  Hand Paddles. Use hand paddles to keep paint well-mixed while you are painting. Using wood-hand paddles allows you to discard them after their use and saves a cleaning job. More efficient metal hand paddles with holes in the blade are also available. However, if a power mixer is available, it is not economical to mix large paint quantities with a hand paddle.

     b.  Power Mixers and Shakers. These tools were covered in Lesson 2.

     c.  Paint Buckets. Several plastic buckets that hold at least 1 1/2 gallons are very useful for mixing paints and for cleaning brushes after their use. A paint-can extender (splash guard) is also handy when you are stirring paints in the original paint container.

     d.  Paint Strainers. Strain paint that has set all night and strain mixtures of dry pigments and oils before use. Also strain any coating that is used in a spray gun. Some strainers are made of paper or cloth, and they are inexpensive and disposable; however, always dispose of used strainers in a fireproof container. Other strainers are made of fine wire mesh; they are cleaned with the same material used to thin the paint mixture.

     e.  Paint Guide. Use a paint guide (Figure 3-21) to help with painting in tight corners and to keep paint off ceilings and trim. Be careful not to get paint on the back of the paint guide.

Figure 3-21. Paint guide

3-4.  Paintbrushes

It is important for you to select good-quality paintbrushes of the correct size and shape for a particular job. You must also know how to care for paintbrushes, store them properly, and reclaim abused paintbrushes.

     a.  Selection. Besides choosing good-quality paintbrushes, you should also select brushes that are the right size and shape for the job. For example, using a small paintbrush on large surfaces not only wastes energy but also prevents proper paint spreading. Applying paint to a smooth surface requires good-quality paintbrushes. They are well-bristled, and the bristles are springy. The bristles of good-quality paintbrushes are flagged at the ends to hold and help spread paint; where as, poor-quality paintbrushes will neither hold paint well or spread it evenly. Figure 3-22 shows the principal paintbrush parts. Good-quality bristles are made from natural or synthetic bristles or a mixture of these materials (Figure 3-23).

Figure 3-22. Principal paintbrush parts

Figure 3-23. Bristles

     b.  Materials, Sizes, and Shapes.

         (1)  Common materials for paintbrushes are hog bristle, nylon, and horsehair

Hog bristle is suitable for applying enamels or oil-based paints that produce a smooth finish on interior or exterior surfaces. The hog bristle is a tapering, hollow tube that forms natural, flagged ends. The flagged end of each bristle is like a little brush. These ends pick up and carry large amounts of paint and help spread the paint evenly on the surface. Hog bristles wear away and continuously form flagged ends as the tube splits.

Nylon is suitable for applying water- or oil-based paints to interior or exterior surfaces. This synthetic bristle is tapered and possesses the resiliency and toughness required for painting operations. Nylon bristle is similar to hog bristle, except the ends of nylon bristle are sanded to make them flag. After they are once flagged, they will continue to flag naturally as the bristle wears away. Do not use nylon bristles to apply lacquer, since the solvents will ruin the bristles. Cleaners containing strong acid, alcohol, or phenolic solutions will damage synthetic bristles.

Horsehair is a substitute for hog bristle. It is made from a horse's mane and/or tail, and it does not have the elasticity and life found in hog bristle. Horsehair does not retain its stiffness when immersed in oil or paint. It lacks toughness, strength, and wearing qualities; and it paints unsatisfactorily.

         (2)  Paintbrushes are available in various sizes and shapes. They are used for the following special purposes:

Large surfaces. Use paintbrushes that measure from 3 to 6 inches wide to apply paint or stain to large wall surfaces (interior or exterior). Flat wall paintbrushes (Figure 3-24) are 3/4 to 1 1/2 inches thick and have bristles from 2 to 7 inches long. Large-surface paintbrushes are usually square-ended and square-edged, with the natural bend of the bristles bending toward the center.

Sash and trim surfaces. Sash and trim paintbrushes (Figure 3-25) vary in shape and size, but most are 1 to 3 inches wide. To get close to windowpanes, one paintbrush has bristles that are beveled like a cold chisel. An angular-cut sash paintbrush is used by some painters when painting hard-to-reach spots. Another type preferred by some painters is almost oval in shape.

Figure 3-24. Flat wall paintbrush

Figure 3-25. Sash and trim paintbrushes

Clear coatings. Use a paintbrush designed for a varnish (Figure 3-26), shellac, or lacquer finish. The brush is usually chisel-shaped, which contributes to smoother applications and prevents lap marks. Paintbrushes are 2 to 4 inches wide and have extra-fine bristles that are 4 to 6 inches long.

Figure 3-26. Chisel-shaped varnish paintbrush

3-5.  Paintbrush Care, Cleaning, Storage, and Reclamation

A paintbrush's life span and usefulness diminishes with improper care, cleaning, and storage. The following will help you prevent or solve problems with paintbrushes:

     a.  Care.

All paintbrushes contain a few short bristles that are not caught in the brushes' ferrule. Before you use a paintbrush, remove the short bristles by striking the bristles against the spread fingers of your hand. Before you start to paint, dip the paintbrush in paint thinner then shake the thinner out; thinner keeps the paint from hardening on the surface of the bristles and makes cleaning easier.

Never stand paintbrushes, wet or dry, on their bristles. The bristles will set in a curve, and no amount of effort will restore them to their original condition.

Never rub bristles over the edge of a container to remove excess materials, as this procedure tends to wear or break the bristles. Instead, tap the brush lightly against the inside of the container above the paint level.

     b.  Cleaning. Once material has hardened in a brush, it is extremely difficult to restore the paintbrush to its original pliability, so you should clean paintbrushes immediately after their use. The best paintbrush cleaners are the solvents used to thin coating materials. To clean a paintbrush that was used in oil-based paint, you will need rubber gloves, eye protection (safety glasses or goggles), cotton rags, a wire brush, at least a gallon of paint thinner, and a paintbrush spinner (optional) (Figure 3-27).

Figure 3-27. Oil-based paint cleaning materials

         (1)  Wear rubber gloves to protect your hands from chemicals. Use a rag to wipe off as much paint as you can from the paintbrush's ferrule (Figure 3-28).

         (2)  Proceed with the directions at paragraph 3-5b(3) below if you poured the paint directly into paint trays. Pour several inches of thinner into a used paint bucket. If you did not pour the paint directly into the paint trays, then wipe any paint off the bucket sides and bottom (Figure 3-29) with the paintbrush that you used for the paint job. This not only cleans the bucket, but it also begins the paintbrush-cleaning process. When the bucket is clean, pour the used thinner into any paint trays that you plan to clean, and pour fresh thinner into the clean bucket.

Figure 3-28. Removing paint off
the furrule with a rag

Figure 3-29. Cleaning the bucket sides
with a paintbrush

         (3)  Pour fresh thinner into a clean paint bucket, and soak the paintbrush in the fresh thinner for a few minutes. Then use a wire brush to "comb" (Figure 3-30) the flat sides and edges of the paintbrush from the ferrule toward the end of the bristles, forcing out the paint. Repeat this process for paint that is trapped inside the bristles near the ferrule.

         (4)  Hold the paintbrush upside down, and bend the bristles back and forth, forcing thinner into the brush's heel (Figure 3-31). Repeat this several times while pouring clean thinner into the bristles. Continue until clear thinner runs out of the paintbrush.

Figure 3-30. Using wire brush to get paint
out of the brushes heel

Figure 3-31. Using your hands to squeeze the bristles
and force cleaner into the heel

         (5)  Use a spinner, if available, to get the last dregs of paint and thinner out of the brush. To do this, place the brush handle into the tangs of the spinner (Figure 3-32). Hold the spinner in the paint bucket or a trash can and pump the spinner until the brush is dry. If you do not have a spinner, spin the brush with your hands inside the paint bucket or a trash can.

Figure 3-32. Spinning the paintbrush

NOTE: Do not pour oil-based paints or thinners down the drain. Thinners and solvents in paints are hazardous materials, and dumping them down a drain ensures that they will end up in the water supply. Check your local regulations for handling hazardous materials.

     c.  Storage. How you store your paintbrushes depends on their future use. Use the following procedures when storing paintbrushes for long periods or overnight:

         (1)  Long periods. When paintbrushes are not to be used for a length of time, clean the bristles with a wire comb then reshape the bristles. When the bristles are straight and parallel, wrap the cleaned paintbrush (Figure 3-33) in its original wrapper or butcher paper. Wrapping keeps the bristles from losing their shape as the paintbrush dries. Store paintbrushes flat, with no weight on the bristles.

Figure 3-33. Wrapping a paintbrush for long storage

         (2)  Overnight. Paintbrushes that are used daily should be kept overnight in a paintbrush keeper (Figure 3-34). Immersing cleaned paintbrush bristles in the proper oil solvent ensures that the bristles will remain soft and pliable. For paintbrushes used in oil-based paint or varnish, use linseed oil in the keeper; for paintbrushes used in lacquer, use lacquer thinner; and for paintbrushes used in shellac, use alcohol. Use enough solvent material to cover the bristles of paintbrushes in the keeper, and remember that brushes in the keeper should not touch the bottom of the keeper or each other.

Figure 3-34. Placing a paintbrush in a
paintbrush keeper for overnight storage

     d.  Reclamation. To reclaim a paint-hardened paintbrush, soak it in a commercial cleaner or a paint remover. A mixture of equal quantities of alcohol, acetone, and benzol is also used to soften a paint-hardened paintbrush (other than nylon). Leave the paintbrush in the solution until the bristles are soft and pliable. If the bristles are badly bent, soak the paintbrush in machine oil and lay the paintbrush on a heated piece of metal until the oil in the bristles sizzles. While the paintbrush is still hot, reshape and bind the bristles with metal wire strips. After the paintbrush has cooled, wash it in mineral spirits and rinse it with benzol or acetone. Wrap the paintbrush in paper to complete the process.

3-6.  Paint Rollers

A paint roller consists of a cylindrical sleeve or cover which slips on to a rotatable cage that is attached to a handle. The most common roller types and sizes are shown in Figure 3-35.

Figure 3-35. Paint rollers

     a.  Cover Materials. The most commonly used cover materials are lamb's wool, mohair, stippler, and high pile:

     b.  Cover Care. Most rollers are constructed with covers that can be removed from the holder for cleaning. The cleaning materials for covers are determined by the type of paints used. For water-based paint, use soap and warm water; for enamel, use mineral spirits or turpentine followed by soap and warm water; and for shellac, use denatured alcohol, followed by soap and warm water. Dry the roller cover thoroughly before storing. When the cover becomes worn or unusable, replace it with a new one.

     c.  Sizes. The size roller you use will depend on where you are painting. Common sizes of rollers are small and industrial:

     d.  Paint Roller Trays. A roller tray (Figure 3-36) is usually a shallow, rectangular container made of metal. The tray is used to apply paint to the roller, and the tray size is determined by the roller's width. To control the amount of paint that stays on the roller, pull the roller over the ridges in the bottom of the tray. Clean the roller first, then clean the tray with the same materials you used to clean the roller.

Figure 3-36. Paint roller and tray

3-7.  Paint Spray Guns

There are many paint spray gun variations: the internal or external mixing, the suction or pressure fed, the bleeder or nonbleeder, and the attached or separate container. Each spray gun may be a combination of any of the variations listed.

     a.  Internal Mixing. This spray gun mixes paint and air inside the gun and spray cap. It is shown on the left side of Figure 3-37. The cap requires less air pressure than the external-mixing spray gun. The cap is popular on small spray guns. The main fault of the internal mixing feature is the tendency for fast-drying materials, which are atomized inside the cap, to collect inside and around the outlet. Pressure fed-spray guns are usually of the internal mixing type.

Figure 3-37. Nozzles of internal- and
external-mixing spray guns

     b.  External Mixing. This spray gun mixes the paint and air outside the gun and spray can. It is shown on the right side of Figure 3-37.

     c.  Bleeder. This spray gun is constructed in such a way that air passes through it at all times. This feature prevents excessive pressure buildups in the compressor. Use this type if the spray gun is to be connected directly to a small compressor.

     d.  Nonbleeder. This spray gun is used in conjunction with a compressor that automatically shuts off when pressure reaches the desired setting. When the trigger on the gun is released, air passing through the gun is stopped.

     e.  Suction Fed. This spray gun is one in which pressurized air passes over the tip of a fluid tube, sucks the fluid from the tube, and sprays the fluid into the airstream. This spray gun is identified by the presence of an air vent in the paint-cup cover. This spray gun is ideal for spraying small areas with lacquer, varnish, or other light materials. However, avoid using this gun when spraying heavy paints, since it will not pull heavy materials up to the nozzle.

     f.  Pressure Fed. This spray gun is made with an airtight container. The pressurized air directed into the container places the fluid under pressure, force the fluid up the fluid tube, and sprays the fluid. This spray gun will spray heavy paints or materials when supplied with a low air volume. It is considered one of the best general-purpose guns for use with regular paints. Pressure fed and suction fed spray-guns are the same, and both types can use internal or external mixing of fluid and air. Since no siphoning effect is necessary for pressure application, it is the best tool for volume painting.

     g.  Attached Container. This spray gun (Figure 3-38) is usually referred to as a cup type since the paint is held in a cup that is attached to the bottom of the gun. Cup-type spray guns, which require only an air hose, are used extensively in military painting.

Figure 3-38. Attached-container spray gun

     h.  Separate Container. This spray gun (Figure 3-39) does not have a paint container or cup attached to the lower portion of the gun. The gun receives paint materials through a fluid hose, which is connected to a separate container called a material pressure-fed paint tank.

Figure 3-39. Separate-container spray gun

     i.  Pressure-Fed Paint Tank.

         (1)  A pressure-fed paint tank (Figure 3-40) is a large metal container that provides paint material at a constant flow and at uniform pressure to the spray gun. The spray gun is connected to the tank with two hoses, one for air and the other for paint material. The tanks range in size from a 2 to 60 gallons. The basic tank consists of a container with a clamp-on lid, an air-pressure regulator, and connections for fluid and air.

Figure 3-40. Pressure-fed paint tank

         (2)  In actual operation, air pressure from a compressor or some other air supply is forced into the paint tank. This air pressure causes the paint to flow out of the tank, through a fluid hose, to the spray gun. When the paint reaches the gun head, it comes in contact with air that is passing through the spray gun, then the paint is atomized and sprayed.

3-8.  Spray-Gun and Paint-Tank Cleaning

Thoroughly clean the paint spray gun and the paint tank after each use. Remove the gun cap, wash and wipe out the tank or the spray-gun cap. Pour a small amount of solvent or thinner into the tank or cup, reassemble and apply air pressure until the solvent or thinner has been blown through the hose and gun. Finish by wiping off the units with a cloth that is moistened with solvent or thinner.

When air or paint passages become clogged with paint, it is necessary to dissemble the units and soak all metal parts in thinner or a paint-remover solution. After the solution has softened the paint in the air or paint passages, take an appropriate-sized soft wire and work it back and forth through the passages until they are open and clean.

NOTE: Do not use lye or any other caustic-alkali solution to clean paint-spraying equipment.

3-9.  Spray-Gun and Paint-Tank Storage

Coat the surfaces of moving parts with a thin oil film whenever a gun or tank is stored for an indefinite time. Lubricate the spray gun air valve daily with light oil. Keep all spray-gun packings, such as the fluid needle packing, soft and pliant by occasional applying oil.

3-10.  Hoses

There are two types of hosesóair and fluid:

     a.  Air. Air hoses are generally lightweight, flexible, kink-free, and will withstand pressures as recommended by the manufacturer. For proper spray-gun equipment operation, the gun must receive an adequate supply of compressed air. Ensure that the required amount of air is applied by using air hoses of the proper size.

     b.  Fluid. Fluid hoses are usually made of synthetic rubber and are used with all types of painting materials, solvents, and oils. Fluid hoses are cleaned at the same time as the gun when thinner or solvent is forced through them by air pressure.

3-11.  Air Compressors

     a.  Air compressors are mechanical units designed to continuously supply compressed air at a specific pressure and volume. Compressors have an electric motor or a gasoline engine. The Army painter is primarily concerned with two types of air compressorsólow pressure and high pressure.

         (1)  Low Pressure. The low-pressure air compressor shown in Figure 3-41, weighs approximately 50 pounds. The overall weight of this unit includes the air-pressure pump, the air-pressure tank, and the driving unit. Since the spray unit is designed to operate on pressures from 20 to 40 pounds per square inch, you should exercise caution against applying higher pressures. Because this gun operates at low pressures, it is not recommended for spraying quick-drying paints, lacquers, or enamels.

Figure 3-41. Low-pressure air compressor (electric motor)

         (2)  High Pressure. Use this compressor for large jobs where heavy-duty spray equipment is required. A high-pressure air compressor is shown in Figure 3-42. Cleaning the air filters and servicing the crankcase are the only maintenance services needed on an air compressor. Some compressors may require additional lubrication in the oil cups, grease cups, or grease-gun fittings. If electricity is available, electric motors are more satisfactory than gasoline engines for driving compressors because electric motors require very little maintenance.

Figure 3-42. High-pressure air compressor (gasoline engine)

     b.  Where electric power is not available, a gasoline engine-driven unit must be used. The preventive maintenance services for a gasoline engine are similar to those for any gasoline engine. The lubricating oil in the crankcase must be kept at the proper level. If it is low, add enough oil to bring the level up to the full mark. In addition, the oil in the crankcase must be changed; and if the engine has an oil filter, the filter cartridge is changed when the oil is renewed. You should also clean the air filter as recommended by the manufacturer. Be sure to check the manufacturer's handbook or the applicable TO for operating instructions and maintenance of the particular type of equipment that you have.

3-12.  Airless Spray Systems

     a.  In an airless spray system (Figure 3-43), the spray is created by forcing paint through a restricted orifice at very high pressure. Paint atomization occurs without the use of air jets, thus the name airless spray. Liquid pressures from 1,900 to 2,600 pounds per square inch are developed in special air-operated, high-pressure pumps and delivered to the gun through a single hose line.

Figure 3-43. Airless spray system

     b.  The system provides a very rapid means of covering large surfaces with a wide-angle spray without producing overspray mist or rebound. The single, small-diameter hose makes gun handling easy. The spray produced has a full wet pattern for quick film buildup. However, the system requires extra care when lapping and stroking to avoid excessive coverage that would result in runs, sags, or wrinkles.

An airless unit with a self-contained heater (Figure 3-44) is also available. The advantage of the hot sprayer is that it uses heat rather than thinner as the viscosity-reducing agent. As a result, the hot sprayer is very compatible with VOC regulations.

Figure 3-44. Airless hot spray system

     c.  The system shown in Figure 3-43, is operated by compressed air; however, some airless models and the hot sprayer are electrically operated. The generation of static electricity and proper daily maintenance are two primary concerns when airless-spray systems are used.

         (1)  Static electricity. It is possible for sparking to occur between a gun and the object being sprayed; this is due to a static-electrical potential that is generated by the high pressure necessary for airless spraying. Sparking can result in explosion and/or fire. To prevent sparking, ensure that both the object being sprayed and the airless equipment are grounded. Do this by attaching a static wire to ground. If the hose does not contain a static-electrical conductor, a static wire must be attached from the spray gun to a ground rod.

         (2)  Daily maintenance. Under no circumstances should paint be permitted to set up, settle out, or dry within the pump. Perform routine maintenance and cleaning daily by using the following steps:

         Step 1. Lubricate the motor when the pump is operating and there are signs of moisture condensing on the cylinder wall during compression action. However, if an airline lubricator is installed, the motor should cause no trouble as long as the amount of oil used can be controlled.

         Step 2. Wipe the inside of the container with a lacquer solvent-soaked rag. Coat the container with clear lacquer to inhibit rust. Solvent that is not compatible with lacquer may cause congealing.

         Step 3. Shut off the air supply to the pump by turning the adjusting knob on the regulator counterclockwise until no spring pressure is felt. Remove pressure from the system by pulling the trigger on the gun, or remove pressure by opening the pressure-release valve on the fluid-strainer assembly and turning the valve clockwise.

         Step 4. Detach the main air-supply hose from the stem at the regulator and attach the hose to the stem on the lift assembly. This lifts the pump assembly from the fluid container.

         Step 5. Remove the fluid container, clean and fill it with approximately 1 gallon of clean solvent, and replace the pump assembly.

         Step 6. Remove the spray cap and strainer assembly from the spray gun, and clean them with solvent.

         Step 7. Detach the main air-supply hose from the stem on the lift assembly, and reattach the base to the stem at the regulator. The pump will lower back into the container.

         Step 8. Close the pressure-release valve, if it was opened, to relieve the system pressure.

         Step 9. Turn the adjusting knob on the regulator clockwise, just far enough so that the pump will operate slowly when the gun trigger is pulled.

         Step 10. Aim the gun nozzle against waste material and hold the trigger back until the fluid in the pump, hose, and gun has been replaced by solvent.

         Step 11. Aim the gun nozzle back into the solvent container, pull the trigger, and circulate the solvent in this manner until the fluid remaining in the system is suspended in solvent. The cleaning action will be better if the system pressure is increased at this point. Lift the inspection cap on the container-cover assembly and aim the nozzle into the container.

         Step 12. Remove pressure from the system by pulling the trigger on the gun or remove pressure by opening the pressure-release valve on the fluid-strainer assembly and turning the valve clockwise.

         Step 13. Turn the handle on the filter cartridge one full turn. Do not turn the handle while the filter is pressurized, or distortion of the unit cartridge will result. If the handle turns hard, it should not be forced but the unit cartridge should be removed for thorough cleaning.

         Step 14. Repeat steps 4, 5, 7, 8, and 9.

         Step 15. Open the pressure-release valve and allow the solvent to circulate for a few seconds.

         Step 16. Repeat steps 3 and 4.

         Step 17. Empty the fluid container and clean the exterior of the pump and container with a solvent-soaked rag.

         Step 18. Wipe off the entire unit with a dry rag.

         Step 19. Detach the hose connection from the stem on the lift assembly and allow the pump assembly to settle into the empty container.

         Step 20. Turn off the air supply.

3-13.  Stationary Compressor Unit

When compressed air is furnished by a large stationary compressor, incline the main air-line leading to the spray guns. Inclining the main line permits the condensed moisture from the compressed air to flow back into the air-pressure tank. Figure 3-45 shows the installation of a stationary compressor unit with the main line sloping toward the air compressor. In this manner, the water is drained by a drain cock which is located at the base of the air-pressure tank.

Figure 3-45. Stationary compressor unit

3-14.  Air Transformer

Supply spray guns with clean, moisture-free, regulated air by installing an air transformer (Figure 3-46) in the main air-line. The air transformer separates oil, dirt, and water from the compressed air before it enters a spray gun; reduces the pressure on the main air-line to the desired working pressure; and provides convenient hose connections for one or more spray guns. The transformer has gauges which indicate the working pressures at the outlets.

Figure 3-46. Air transformer

Whenever an air transformer has only one working-pressure regulator, all attached spray guns will have the same working pressure. However, if the transformer has two working-pressure regulators, as shown in Figure 3-46, the attached spray guns are regulated by different working pressures. Use an air transformer in all finishing paint shops where a supply of clean, moisture-free, regulated air is required. When a regulated supply of air is available, a condenser is used to separate oil and moisture from the air. Conventional spray systems have basic similarities. There must be an adequate source of compressed air, a paint supply, and a spray gun for controlling the combination of air and paint in an atomized cloud against the surface to be coated.

3-15.  Spray Booth

A permanent spray-paint shop requires a well-ventilated and well-illuminated spray booth. Figure 3-47, shows a portable spray booth that is ventilated by the deflector plate shown in the back. It is illuminated by floodlights recessed in the walls of the booth. Portable floodlights should also be available for the spray booth to provide good, direct light on the area being painted. All lights must be of the vaporproof type.

Figure 3-47. Portable spray booth

3-16.  Wiping Rags and Drop Cloths

Carry wiping rags at all times to wipe up spills and splatters before they dry on unprotected surfaces. Drop cloths are used to protect furniture and floors and are available in canvas, rubberized fabrics, plastic, and impregnated paper. Plastic drop cloths are the most popular because they are inexpensive and can be discarded when they become soiled.