Guide to Working with Plastics: A Wealth of Fillers and Paints--Spraying the Professional Way

The versatility and adaptability of plastic- base paints and sealers suits them to the fastest of all application techniques: spray-painting. With a portable spray gun, it’s possible to apply a uniform, mirror- smooth coating more quickly than with a brush or a roller, or by any other manual method.

Virtually any large surface, from fine wood to coarse cinder block, can be spray-painted. Even small surfaces and trim can be sprayed with careful masking, although for very small areas the time needed for masking may exceed the time saved by spraying.

Equipment for spray painting ranges in complexity from disposable, albeit ex pensive, aerosol cans, which deliver a fine coating mist for small finishing projects, to high-capacity compressor-driven spray guns that can be rented from tool-supply stores. Between these extremes lies a tool that can perform almost all of the jobs handled by conventional compressor-powered units, and with a real savings in paint: the lightweight air less sprayer. Conventional sprayers use compressed air to create a misty mixture of paint and air. The airless guns employ a small but powerful electric pump to propel only droplets of paint through their nozzles, yielding more precise application and far less overspray than the compressor-driven sprayers.

Before painting with any airless sprayer, familiarize yourself thoroughly with its operation. Because models differ from manufacturer to manufacturer, read the manual supplied with your sprayer—and note the safety precautions in the box at right. Then, if you have never spray- painted before, fill the spray gun with water and get the feel of using it by spraying newspapers hung vertically.

Although virtually any plastic-base coating can be sprayed, it generally must be diluted before use. Most sprayers require paint about 25 percent thinner than brushing consistency. The paint must also be free of impurities. If you notice any floating skin or dirt, filter the paint through twice-folded cheese cloth. Remember, too, that careful surface preparation is just as important for spraying as for any other method of application

In addition, spray painting calls for extra caution in preparing the surfaces that you don’t wish to paint. Because atomized paint can get picked up by air cur rents and drift a considerable distance— especially outdoors—protect the nearby surfaces with dropcloths and newspapers held down with masking tape.

Finally, whenever you finish using a spray gun, clean its mechanism by flushing it with a solvent compatible with the paint that was sprayed.

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--The airless sprayer. The motive force for an airless spray gun comes from a powerful electro magnetic motor. Turned on and off by a trigger switch—and regulated in velocity by a control knob on the rear of its insulated housing—the motor drives a spring-loaded piston back and forth. The moving piston sucks paint from the container, through a mesh filter and suction tube, to the cylindrical paint chamber, and then forces the paint from the chamber, past the spring-loaded spray valve and out through the nozzle, whose tiny orifice directs minute droplets of paint toward the surface being coated.

For large painting jobs, the small paint container may be removed and an extended exhaust suction tube (not shown) fitted directly to the nipples on the bottom of the paint chamber. The long tube, fitted with a clip and a filter, is then immersed directly in a large bucket of paint.

== The Safe Use of Hazardous Equipment ==

Airless sprayers must be treated with the utmost respect. Typical models spray at pressures as high as 1,500 pounds per square inch, enough to actually force paint through your skin. When operating a spray gun, never point it at yourself or anyone else. And never put your hand near the nozzle of an operating gun, not even for a moment.

Should you accidentally inject paint under your skin, get medical help immediately. Note the resin and solvents of the paint you were using, so that the physician can check with the National Poison Center, by telephone, for proper treatment.

To prevent accidental fires, don’t smoke in a room where you are spraying solvent-thinned paints or paints whose base resins are flammable; these include polyurethanes, epoxies and vinyls. Extinguish any gas pilot lights in the room. To guard against electric sparks, make sure that any ex tension cord you use has a grounding wire and is plugged into a three-wire grounded receptacle. Before painting, don a charcoal-cartridge respirator and, when painting indoors, provide for adequate ventilation. Keep a fire extinguisher on hand.

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--Readying paint and sprayer. Dip a viscosity measuring cup, which commonly comes with an airless sprayer, into the paint. Lift the cup, and lime how long it takes for the paint to drain out through the hole in the bottom; compare this time with the time the sprayer manufacturer recommends. If necessary, mix in a small amount of the proper solvent, then test the consistency again. Continue thinning and testing until the paint runs out the hole within the time recommended for your sprayer.

Filter the paint through cheesecloth if necessary, and pour it into the paint container of the sprayer, filling the container. Aim the gun at newspapers taped to a wall, and adjust the control knob until the paint sprays out in a uniform wedge-shaped pattern. Spattering paint indicates that the velocity is set too low; paint running down the paper indicates too high a setting.

--A proper indoor spraying setup. To guarantee a safe and neat job, small surfaces you don’t wish to coat should be covered with strips of masking tape. Shield larger areas with drop- cloths. Wear a charcoal cartridge respirator when spraying, and install a fan in the nearest window to draw away fumes. If you are far from a window, carry fumes to it by rigging plastic dryer duct from the fan to the work area. Keep a fire extinguisher—either a carbon-dioxide or a dry-chemical one—handy in case of fire.

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--Spraying walls. For large jobs, supply paint to the sprayer through an extension tube rigged to a large paint container. Hold the gun horizontal to the wall surface and, while spraying, move your entire arm up and down or left and right, keeping the nozzle about 8 inches from the wall (inset); don’t swing your arm in an arc, which would vary the distance of the nozzle from the wall, bringing it closer at the center of each sweep, farther at the ends. Large, smooth walls are best covered with a crosshatch pattern, the paint applied first with vertical passes, then horizontal ones. For walls that are divided horizontally by moldings or clapboards, use overlap- ping horizontal passes only.

--Coating horizontal surfaces. To paint ceilings or floors, replace the regular nozzle with a flexible extension nozzle. The extension—available for most airless sprayers—is made of soft copper tubing that you can bend with your fingers, thus aiming the spray up or down at horizontal surfaces without making it necessary for you to tip the gun or aim it directly overhead.