Leonard Brooks Paints

PAINT SPRAYING TECHNIQUES

Gun Distance

Maintain a hand span (approx 8in) between your gun and the surface being painted. HVLP guns need to be set closer (usually around 6/7in) to the work. This avoids paint sags or dry spraying.

Strokes

Always point the gun at right angles to the surface you are painting. Spray in horizontal strokes up to 3ft long, flexing the wrist but keeping your arm fairly stiff and swaying the whole body when necessary.

Speed

Move the gun at a speed which ensures a full wet coat for the area covered by each stroke.

Don't ark

Never allow the gun to arc during strokes - this applies too much paint in the middle of the stroke and too little at each end. Never point the gun up or down when spraying a vehicle surface.

Triggering

The trigger controls the gun's action. Use it at the beginning and end of each stroke to feather the paint applied.Begin the stroke, pull the trigger, then release the trigger just before ending the stroke. This technique avoids the dangers of paint sag due to double coating where strokes overlap.

Overlapping

Every stroke should overlap the previous stroke by approx. 50%. In conjunction with triggering, overlapping blends or feathers each sprayed edge, so that there is no unevenness or striping after drying. Always paint in sections small enough to ensure that your next overlap is with a wet edge. Overlapping with a dry edge creates stripes.

Large Areas

For large areas such as commercial vehicle sides, work in 3ft sections starting at the top. Overlap each section by about 4in using the triggering technique. Never let one area dry off before moving to the next.

Horizontal Surfaces

Start at the edge nearest to you and work away from yourself, taking care to keep gun hoses away from the wet surface. It is OK to angle the gun slightly to prevent overspray falling on the wet surface.

Edges

Spray edges before main surfaces, using a modified banding technique. One stroke along the edge will also put a band along the adjoining horizontal surface. After this, carry on with the normal horizontal method, taking care to avoid hose contact with the wet edge.

Keep the dust down

Since spray painting uses compressed air, a strong draught is created in the direction of the spray. When painting near to ground level, it is a good idea to wet the ground close to your job, to prevent dust blowing up onto the newly painted surface.

Spot Priming

When applying primer to a spot repair, use the triggering technique to avoid spraying beyond the feathered edge, except on the last coat. On this coat overlapping is OK, but not more than 2 or 3 ins. Let each coat flash dry until it's flat before applying the next. Never fan with air to speed up drying - this contaminates the finish with airborne moisture and dirt.

Masking

Always mask off the areas not to be painted and remove external trim components wherever possible.

Paint leaks -

Paint leaking from the gun is a sure indication that something is wrong, even if you have not noticed any problems in your spray patterns. If the paint is leaking from the front of the gun, the fluid needle is not seating properly. This may be caused by a worn or damaged fluid tip or  needle, dirt or dried paint stuck in the fluid tip, incorrect matching of fluid needle and tip, a too tightly screwed up fluid packing needle or a broken fluid needle spring. If the leak is coming from the fluid needle packing nut, it indicates that the nut is too loose or that the packing is in need of lubrication or is worn.

Air leaks -

Air leaking from the gun is usually caused by dirt on, or wear in, the air valve or its seating, a broken air valve spring, a sticking or bent valve stem, a too tightly adjusted air valve packing nut or a damaged air valve gasket.

Spray fog -

Paint which ends up in the air rather than on the panel to be painted is usually caused by an excess of thinners in the paint or too high an air atomisation pressure. It can also be caused by holding the gun too far from, or not keeping it parallel to, the surface to be painted.

Dry spray pattern -

This results from a shortage of paint caused by too high an air pressure, incorrectly thinned paint, or the gun being held too far from the work. Adjusting the gun fluid and spray pattern controls may also help resolve the problem. Holding the gun too far from the surface, using too high an air pressure or a thinner which dries too quickly will result in a thin, coarse finish. If your gun simply refuses to spray, check that the airlines are intact and that air is actually getting to the gun, that the fluid adjusting screw is open, and that the fluid is not too heavy, if using a suction fed gun.

Air Lines and Air Control Equipment

It is important that the galvanised tube or airline taking air from the compressor to the air transformer is as short as possible and of a diameter which allows a sufficient volume of air to arrive at the spray gun with as little drop in pressure as possible. The larger the tube diameter, the less the pressure drops. Power is lost from the air through friction as it travels along the pipe, and this effect is increased where the air has to travel round sharp bends. It is vital that all line couplings are compatible with the pipe size. It is no use having a well designed air supply system with good sized pipes, then strangling it with couplings of inferior design and/or inadequate internal diameter. Leakage should be kept to a minimum, as apart from reduced efficiency, compressed air is not cheap and badly fitted couplings and leaking airlines can cost the bodyshop hundreds of pounds a year in wasted energy.

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