O-Gee Paint

Spraying with a cup gun used to be limited to solvent base coatings such as alkyds and lacquers and these are still the easiest to apply. But people are moving away from solvent based finishes and waterbase products are becoming more and more prevalent. Latex finishes can be sprayed from a conventional cup gun with a few adjustments to the gun and technique.
Cup guns come in two generic types: HVLP and Conventional. The primary difference is the working pressure at the air cap. HVLP uses six to ten psi whereas conventional guns use anywhere from 25 to 50 psi. Because of the lower pressure, HVLP guns require the fluid to be forced up to the fluid to the nozzle rather than relying on the siphon effect of the moving air. HVLP further breaks down into turbine or compressor air delivery systems. If you are planning on purchasing a n HVLP turbine and gun, look for units with more stages. CapSpray’s 5-stage CS9900 turbine is the most powerful on the market at this time. More stages give higher pressure so you’ll be able to spray a wider range of viscosities. Because a turbine provides air in the compression phase, they create warm air blowing through the gun. This can be a good thing to help dry evaporate moisture out of the paint as it is being sprayed but can also lead to tip clogging so keep a damp rag around to wipe the nozzle as build up occurs.
It is important to select the right paints. Many paints have a heavy consistency that makes them difficult to thin and therefore difficult to atomize. These will come out bumpy with a texture like an orange peel. Select paints with a fairly thin consistency to begin with and you’ll be one step ahead. Thinner finishes like Moore’s Waterborne Satin Impervo or Insl-x’s Silathane II and Cabinet Coat have a loose feel to them and spray very well unthinned with 4 stage turbines systems.
If you have a professional spray gun chances are you can get different size needle nozzle sets for it. These are generally numbered from two to six or seven. Different guns use different orifice diameters even though they may have the same number. Larger diameter nozzles allow for faster production. Production speed is often a subjective issue, with latex paints you’ll want at least a number five needle nozzle kit. If you can’t change the fluid set and are stuck with a small diameter nozzle, you may need to slow your movement over the surface quite a bit to allow enough paint to fully wet the surface. Also, if you’re using an air compressor system, you’ll probably need to turn up the pressure higher than you would with an alkyd type finish.
Be sure to strain the paint before it goes into the cup. There always seems to be a little bit of junk in my paint that clogs the nozzle or splats on an otherwise nice finish. Apply enough paint during your passes over the surface so it makes a nice wet finish. If the finish is not wet enough it will not flow properly and will look bumpy. Then the only way to smooth it will be sanding later. Water base paints set up quickly and thin mist coats generally will not re-wet and flow like alkyds will. Latex is bug free pretty quick but takes longer to get truly hard enough to sand between coats compared to an alkyd. Once again, paint selection makes a difference.
Some paints still require thinning and my experience is that thinning with water is not good. Water can cause the paint to lose body too quickly. I have also found that it doesn’t evaporate away quick enough in Miami and seems to squeeze out of the coating and form droplets on the paint film. My best results are had when thinning with a clear finish product like a thin water base varnish. My current favorite product to reduce viscosity is Seal-Krete’s Wet Look. I have tried a number of different varnishes in the past with results that were always better than working with water alone. The clear finishes blend in with the paint and reduce its viscosity while retaining its ability to lay out without the paint separating or water condensing. Flood’s Floetrol is too heavy for my liking and doesn’t really thin out the paint at all. The Wet Look is really thin and blows out like water. It also makes a nice clear overcoat if you like shiny finishes. The truly hard part of spraying latex paints
Recently, I have been shooting Modern Masters metallic finishes, Bruning (now Insl-x) Silathane II, and some Seal-Krete “Wet Look” with my compressor gun. Latex paints are a bit harder to work with but with a few modifications can be quite successful.

Dec052007

Tags: air, conventional, latex, paint, spray, sprayers, h.v.l.p.

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