Paint with a Compressed Air Sprayer

Compressed air paint sprayers can save money, offer flexibility, and decrease pollution by using air, rather than aerosol propellants to spray your paint. This technique requires an investment, but for frequent maintenance or shop use, the cost can be well worth it. The unit used in the illustrations is known as a LVLP(low volume, low pressure) sprayer, which applies paint at a lower rate, decreasing airborn paritculates, while applying less paint on each pass.

Steps

 * 1)  [[Image:IMG_1859_635.jpg|thumb|Paint and appropriate thinner.]]Select your paint.  Oil based enamels are most easily used with a compressed air sprayer, but acrylics and latex paints can be sprayed if they are modified with a suitable conditioner.  This will thin the paint so that it will flow through the siphon tube and out the orifice.
 * 2)  [[Image:IMG_1876_429.jpg|thumb|Protect adjacent areas from over spray]]Prepare the area where you will paint.  For "fixed" projects, like the one illustrated here, you will need to protect adjacent surfaces, and make sure you have adequate ventilation.  Protect nearby surfaces from "over spray" with masking or painter's tape and painter's paper or newspapers.
 * 3)  Prepare the surface to be painted.  Grind, brush, or sand off rust and corrosion from metal, removing all oil, dust, or dirt, and make sure it is dry.  Wash the surface: for oil-based paints, use mineral spirits; for latex or acrylic paints, use soap and water, rinsing thoroughly.
 * 4)  Prime the surface, if required.  You can use the sprayer to apply the primer, following the steps below as if it were paint, or it may be applied with a brush or roller, then sanded smooth if needed.
 * 5)  Set your paint and thinner on a suitable surface so that spills will not damage anything.  Place a drop cloth, sheet plastic, scrap lumber, or other material on the ground, floor, or a table for mixing.
 * 6)  Turn on the air compressor.  You will use some air for priming and testing your sprayer, so let it build up pressure while you get your paint ready.  The compressor should have a regulator to allow you to set the pressure for the sprayer correctly, otherwise, fluctuations will occur as the pressure rises and falls while you are spraying.
 * 7)  [[Image:IMG_1877_932.jpg|thumb|Regulator gauges on a small compressor]]Adjust the regulator on the compressor to between 12 and 25 PSI (pounds per square inch), depending on your sprayer.  Attach the air hose coupling to the sprayer.  Make sure it is tight, and you may wrap the threads with Teflon tape to insure an airtight seal.  This does not apply if your sprayer and hose are equipped with quick connect couplings.
 * 8)  Pour a small amount of thinner into the paint cup, (the reservoir attached to the bottom of your spray gun).  Use just enough to submerge the siphon tube in it.
 * 9)  [[Image:IMG_1857_79.jpg|thumb|Upper screw is the air flow, lower is the fluid metering valve.]]Open the metering valve slightly.  This is usually the lower of two screws above the handle (pistol grip) of the sprayer.
 * 10)  Mix enough paint to do your project.  After opening your can of paint, mix it thoroughly, then pour enough of it to do the job into a separate, clean container.  If the paint has been stored for any length of time, it is a good idea to strain it through a paint filter to remove any lumps of hardened paint which may have formed.  These lumps can stop up the siphon tube or the metering valve, causing the flow of paint to stop.
 * 11)  Thin the paint you have poured with a suitable thinner, to allow it to flow freely through the siphon tube, metering valve (fluid) assembly, and out the nozzle.  Different sprayers are calibrated and the orifices are differently sized, but usually the paint should be thinned about 15 to 20% for a good flow.  Notice how thin the paint looks when you use an aerosol spray paint, and it will give you an idea of what you are looking for.
 * 12)  Prime the sprayer.  Aim the nozzle into a waste bucket, and squeeze the trigger.  It usually takes a few seconds for the sprayer system to prime with liquid, so at first, only air will come out of the nozzle.  After a moment, you should get a flow of paint thinner.  If no thinner comes out of the nozzle, you may have to disassemble the sprayer to check for stoppages or loose seals in the siphon tube assembly.
 * 13)  Empty the spray cup of any remaining thinner.  A funnel helps, here, so you can return it to the original container.  Mineral spirits and turpentine (two common thinners) are flammable solvents, and should only be stored in their original containers.
 * 14)  Fill the paint cup about 2/3 full of paint, and lock it on to the sprayer.  Whether the spray cup attaches to the bottom of the sprayer with a clamping assembly and hooks, or is threaded, be sure to attach it securely.  You do not want the spray cup to drop off suddenly while in use.
 * 15)  Hold the sprayer about 5-10 inches from the surface.  Begin moving the spray gun in a side to side, or up and down sweeping motion, parallel to the surface.  If you have never used this type of paint applicator before, practice holding and swinging it for a moment, to get a feel for the balance and weight of it.
 * 16)  [[Image:IMG_1864_798.jpg|thumb|Keep the sprayer moving!]]Squeeze the trigger to spray the paint.  Keep the sprayer moving whenever the trigger is squeezed, to avoid drips and runs caused by over application.
 * 17)  [[Image:IMG_1875_730.jpg|thumb|Spraying paint]]Overlap each pass slightly, so the "feathered" edge at the edge of the spray pattern gets an equal coverage of paint.  Watch for drips and runs, moving fast enough to keep the paint from getting too thick as you spray.
 * 18)  Refill the paint cup as needed, until the project is done.  Do not allow the sprayer to set with paint in it. If you need a break, remove the cup, and spray some thinner through the sprayer before leaving it unused.
 * 19)  Clean the sprayer by pouring out the unused paint.  If you have a significant amount of paint left, you can return it to the original can, but remember the amount you return to the can has already been thinned, so the next time you use it, you may need to adjust the amount of thinner used.  While you have the spray cup removed, rinse it with thinner, along with the siphon tube, and wipe any excess paint off of and out of it.  Next, fill the spray cup about 1/4 full paint thinner, slosh it around in the spray cup to rinse the inside, then spray it through the sprayer until it comes out clear.  If there is too much paint left in the cup or the spray assembly, you may have to repeat this step 2 or more times.
 * 20)  Allow the paint to dry, then re coat if desired. For most paints, a good, even "wet" coat is sufficient, but a second coat may give a more durable finish.  Sanding between coats is recommended for varnishes, polyurethane finishes, and other glossy paints, to improve the bond between the coats.
 * 21)  Remove all masking tape and paper as soon as the final coat is dry.  Leaving the tape on the surface for an extended period will allow the adhesive to "set", making it difficult to remove.

Tips

 * Read the instruction or operator's manual for your sprayer. You should be familiar with the capacity, viscosity, and type of paint your sprayer will apply. The controls on the sprayer used in the photos are fairly typical for this type sprayer.  The upper control valve regulates air volume, the lower one meters the paint flow. The front of the nozzle is held in place with a threaded ring, and the pattern can be changed from vertical to horizontal by turning it.
 * It wouldn't hurt to use an air line filter or a dryer to remove moisture and dirt from the compressed air stream. These accessories can be added for little over $100.
 * Mix enough paint for the complete job, if possible, since any future mixes may differ slightly.
 * Clean the paint sprayer thoroughly after use. For dried-on oil based paints, you may have to use acetone or lacquer thinner to dissolve it.
 * Paint either horizontally or vertically, but try not to do both on one project, as there may be a slight texturing of the surface that may have a different appearance where you change directions.
 * Use a catalytic reducer for automotive finishes. It is especially formulated to speed the drying time and prevent runs, without affecting the finish or color or the paint.
 * Be aware of over spray. In windy, outdoor conditions, airborne paint particles may drift farther than you expect.
 * Using a compressed air sprayer instead of aerosol cans allows you to paint with custom colors, decreases air pollution, and saves money. It does, however, release significant VOCs (volatile organic compounds), which are used as solvents in most paint formulations.
 * Unused paint can be replaced in the original container as long as you remix it before using it again later, and remember that it has been thinned somewhat.

Warnings

 * Some paint products use highly flammable solvents, particularly "dry fall" or laquer based paints. Avoid sparks and open flames, and do not allow fumes to accumulate in confined spaces.
 * Avoid breathing atomized paint or paint thinner fumes.
 * Paint only in a well ventilated area.
 * Wear a respirator for any extended periods of painting.
 * Never disconnect the air hose while the compressor is charged.
 * Paints using a catalyst (two part paints) and epoxy paints can not be returned to the original can they Must be used or disposed of properly once mixed.

Things You'll Need

 * Air compressor with regulator (and a drier, preferably)
 * Air hose and couplings
 * Spray gun
 * Paint and thinner
 * Masking tape and paper
 * Sandpaper
 * Cloth

Related Tips and Steps

 * How to Get Dried Masking Tape off a Painted Surface
 * How to Use an Airless Paint Sprayer
 * How to Use a Paint Roller
 * How to Use a Paint Brush
 * How to Paint Stainless Steel
 * How to Get Spray Paint off of a Car
 * How to Paint a Car