DIY Spray-painting using a Spray Gun

Spray Gun Tips


Many, if not most of us, make use of spray paints using canned spray very much like the aerosols. However a spray gun, though expensive, is a handy tool to have if you do a lot of work.

They are available in a range of sizes. There are small airbrush versions that are ideal for craft work. Others are far bigger, some requiring the use of a compressor, which provides the high-pressure air that some spray guns use to produce the paint spray, and others that use a rapidly reciprocating piston to pressurise the paint at the nozzle.


So, let’s spray for the day…

  • As with any paint job, unless the surface has been properly prepared, you will not get the result you want. So to start off by preparing your surface.
    • A glazed ceramic surface needs to be roughened a little with fine grade sandpaper – 320 grit. This is to ‘key’ it so that the paint can ‘grip’ to the surface.
    • Fabric and vinyl needs to be washed and be thoroughly dry before the paint is applied. It is also good to check that the fabric has not had any UV or other protection applied during the manufacturing process that might prevent proper adhesion (this is more likely to have been applied in the case of fabrics or vinyl manufactured for outdoor use).
    • Glass is best painted if the surface has been etched beforehand, again to provide a ‘key’ to which the paint can adhere.
    • Metal must be cleaned of any rust, oil, grease or grit deposits before being painted.
    • Plastic or PVC needs to be cleaned before application. New plastics can be cleaned with a paint thinner while you can use an ammonia-base cleaner on older plastics. In either case, you can also scrub the surface with a good detergent and scouring powder, which is then thoroughly rinsed off in clean water and left to dry. It’s a good idea to ‘key’ the surface by giving it a light, fine sanding with fine grit sandpaper – 320 grit or thereabout. The object is just to roughen the surface ever so slightly so that the paint has something to ‘grip’. Ensure that you give the surface a wipe-down with a clean dry cloth afterwards to remove any sanding debris.
    • As with all surfaces, wood must also be clean and sanded smooth. If you are spraying a somewhat patchy previously painted surface. It is best to remove all the old paint (otherwise you can get the old paint showing through and/or giving you an uneven surface). Apply and sand down an undercoat as you would if applying the paint with a brush or roller.

Tools:

  • Can of spray paint of the required colour or spray gun (some versions require a compressor; others use a mechanical piston or other means to produce the paint jet.

Method:

  1. There is a range of very efficient and portable spray units on the market these days – just read the instructions first, before use.


  2. Spray Painting Tips 1

  3. Never do this: Apply spray without a suitable backdrop protection. And in this case, note that the sprayer is designed for use only with paints with a non-flammable base.


  4. Spray Painting Tips 2

  5. Aerosol-type spray paint is excellent for touch-up jobs in and around the home but sometimes paint dries and blocks the nozzle, so you either try to unblock it – which can affect the way the spray mist lands on the surface, find another nozzle, or dump the can and buy a new one. The solution is to turn the can upside-down and spray for a split second, clearing the nozzle of paint. Do not do this for more than a split second however: the moment you see no paint is being ejected, stop – otherwise you will waste the pressurisation agent and can still end up having to buy a new can while the present one is still quite full.


  6. Spray Painting Tips 3

  7. For touch-ups, in this case, the corner of a car bonnet needs a little TLC.


  8. Spray Painting Tips 4

  9. So, mask it off, and rather do too much than too little.


  10. Spray Painting Tips 5

  11. Now, if you apply masking tape directly to the surface to mask off the area to be touched up, you will get a sharp, unsightly edge. The solution is to fold a piece of paper or cardboard to form a bridge with the bridge part being about 10mm above the surface.


  12. Spray Painting Tips 6

  13. Now spray as normal. The bridge will still mask off the area you do not want to paint, but where it will allow the paint mist to settle diffusely so you don’t get a sharp edge.


  14. Spray Painting Tips 7

  15. The completed job – can you spot where the new paint ends? Nope, nor can we.


  16. Spray Painting Tips 8

  17. On the left, spraying straight on 90°. On the right, spraying at an acute angle and more paint lands where it needs to.


  18. Spray Painting Angle Diagram

      Project Guide:

      Time: Depends on size of project/touch-up
      Cost: Depends on size of project/touch-up
      Skill: 1
      Assistant: No

      These materials are available at selected Mica Stores. To find out which Mica is nearest to you and whether or not they stock the items required, please go to www.mica.co.za, find your store and call them. If your local Mica does not stock exactly what you need, they will be able to order it for you or suggest an alternative product or a reputable source.


      DIY spray-painting tips:

      • Read the instructions. Too many of us do not, but it pays to read the manufacturer’s instructions carefully. They will provide information as to spraying distance, hints and tips on how to achieve the desired result, paint viscosity, what paints can be used or not (solvent-based or water-based) and other information that will help you get achieve the desired result.
      • Do your spray painting in a well-ventilated area.
      • Place the work-piece on a large drop-cloth or ensure that whatever is not to be sprayed is well protected with taped down newspaper or other cover.
      • Spray on a calm day if outdoors to avoid paint going everywhere.
      • To safeguard your lungs, wear a facemask and ensure you also protect your clothes. You can use a large black plastic refuse bag with three holes cut for head and arms to avoid damaging your clothes.
      • When spraying small items, placing them in a cardboard box will keep the spray confined.
      • Before spraying, do a test or tests on a scrap item with the same surface as the work piece and adjust your spraying distance, movement of the spray and so on until you achieve the right result.
      • Never stop the spray moving – that’s when it deposits a lot of paint and you get runoff.
      • Rather apply a number of thin coats than one thicker one – again, less risk of runoff.
      • For an even coat, sweep the can or spray gun vertically and horizontally past the object and beyond it on all sides as you spray. If you don’t go beyond the work piece, for the split second that it takes for the nozzle to start back in the opposition direction, extra paint will be deposited on the work piece; going beyond it will confine the overspray to the drop cloth.
      • Alternatively, spray in short bursts while keeping the nozzle on the move at a steady pace.
      • If spraying a mesh (cooling fan mesh guards sometimes rust and need a touch-up), apply the spray at a very acute angle, rather than from straight ahead… the same applies when spraying a number of burglar bars, for example. (see illustration) by spraying at an acute angle of 15-20° to the surface rather than 90°, paint that misses on bar, for example, will land on those adjacent to it. To put it another way, if you spray bars with a 10mmØ and they are 50mm apart, and your spray pattern is 100mm wide, 80% of the spray will miss the bars. Think of looking through a diamond mesh fence… straight on, you can see clearly, put your eye close to it and look down its length, and it blocks your view.
      • When applying multiple coats, ensure you allow sufficient time for each coat to dry before applying the next – follow the manufacturer’s guidelines – but bear in mind that paint generally takes longer to dry completely in cool or wet weather.
      • If you do a lot of spray painting, making up a rotating platform like a Lazy Susan allows you to rotate the work piece to apply an even coat, without you have to move around it yourself, and because you are spraying from one direction only, shielding whatever is behind the work piece is much simpler.