One of the most interesting parts of my job is visiting car manufacturers in different countries. I always enjoy this feeling of an accurate, well-managed producing machine. It gives you a clear vision, a benchmark, of how things must work in a regular bodyshop. A paint shop in OEM plant is a special place. It is very-very clean. Everything is done in order to prevent dust and dirt from coming to the painted surface. However, even in the car plants with all the measures taken, on average, about 4-5 dust nibs are usually revealed during the inspection process. And this happens under conditions close to an operating room in a hospital! Thus, it is not difficult to understand why more than 50% of car defects in a regular bodyshop, are mere dust inclusions in the basecoat/clearcoat film. I think you would agree with me that majority of the body paint shops are anything but neat and tidy.
What is a dust nib?
Actually we call this type of paint defects with different names. Dirt contamination, spikes, grits, nibs, seeds, grains, specks, bits… Yet, no matter how you call them, the meaning is simple; those are foreign particles, which are not supposed to be there. They are projecting from the paint film, undermining your overall job and effort.
Dust nibs could be of a different origin:
– Simple air-borne dust
– Human hair
– Lint from wiping materials
– Abrasive grains
– Cloth fibers
– Dried overspray
– Airline dirt (parts rubber air hose, for example)
– Fibers from the spray booth filters etc
How to prevent dust contaminations?
It is always better and easier to prevent a problem rather than remedy. So, what shall we do in order to avoid the costly and time consuming re-works?
1. The most important way to keep your paint job free from dust inclusions is to preserve the working area and spray booth clean and tidy.
2. Wear anti-static tear-proof working overalls while spraying.
3. Regularly check and maintain air supply system. Worn-out air hose will throw small rubber particles in the compressed air line.
4. Change and clean routinely air filters.
5. Clean thoroughly your spray guns and blowing guns.
6. Protect spray booth walls from overspray by applying booth mask tacky coating or special film. Dried overspray on the walls can easily get into the air circulating in the booth and stick to the wet painted surface.
7. According to the European laws sine 1991, a spray booth must be running at negative pressure, in order to prevent airborne hazardous paint mist escaping the cabin. This means that if we open frequently the doors of spray booth or if wall panels are not properly fit, seams with improper insulation, gaskets worn-off etc, the dust from outside will be attracted inside the spraying area. Inspect systematically your spray booth condition for leakage. I have to add that in practice many paint sprayers tune their spray booths create excess pressure inside to avoid dust to get in.
8. Always wash a vehicle before even starting preparation jobs.
9. Air blow the vehicle before entering a spray booth.
10. Use anti-static wipes on plastic car parts prior paint application. Plastic attracts air-borne dust. Pay attention to bumpers, plastic rims, mirrors etc
11. Use high-quality dedicated, preferably non-woven wipes with degreaser and anti-silicon cleaner.
12. Clean routinely all the surface to be painted with a high quality tack rag.
13. Use only dedicated masking film with corona treatment. This film is designed to hold overspray, avoiding peel-off of dry paint.
14. Use high quality Kraft masking paper. Newspapers or other types of paper are made of recycled raw material. Such masking paper is full of fibers on its edges, which will fly over the place as soon as air from a spray gun will hit the surface of the car.
Usually dust nibs within a clearcoat film can be removed by microabrasives P1500-P2000 and subsequent polishing. However, dust inclusions within basecoat film must be re-sprayed. What is important to remember that removing a dust nib can be done only after the clearcoat is fully cured.