O-Gee Paint

When I’m spraying latex paints through my cup gun I find I often need to reduce the viscosity. Using water isn’t good because the paint usually begins to lose integrity just as it achieves the flow I desire. Instead I add small amounts of a thin water-base liquid such as clear varnish or masonry water-proofer like Seal-Krete. This allows the paint to be thinned without losing the ability to hold itself together. Yes, it changes the sheen and the ratios have to be monitored to keep from having a variety of gloss levels but my projects are typically small enough that this doesn’t bother me and the ease of spraying is worth the effort. I use a compressor gun and compressor guns shoot expanding. and therefore cool, air. This is not true with turbine HVLP sprayers.

HVLP sprayers blow warm, sometimes hot, air. I saw a situation this past month where a painter had used his CAPSpray CS9100 to spray Insl-x Silathane II Acrylic Semi-Gloss on doors and frames in an office redo. His problem, as he related it to me was that it had an uneven sheen. Of all the paints we sell, Silathane II is one of my absolute favorites, mostly because it is hard enough that things do not stick to the dry film. This is immensely important on doors and shelves where contact is constantly being made.

At any rate, he’s spraying these doors and its flashing so when the door is open the sheen looks as uneven as can be. Turns out that the heat of the sprayer and warmth of the room caused the paint to dry too quickly. The atomized paint was drying in the air and the paint on the door had begun to set to the point where they would not flow and meld together. The flashing was simply dust-like paint attached to the door.

The only way to control this effect would be to use an extender that would slow the drying of the paint. Extenders are usually a kind of slow drying solvent along with a minor amount of resin to hold it all together. When mixed with water-based paint it slows down evaporation and allows a longer period of time for coalescence. This is becoming more important with the faster drying finishes that are being developed. Benjamin Moore’s waterborne paints dry so quickly that they sometimes need an extender. For use with their AURA and Regal lines of paints, Ben Moore has an extender to make it more workable. Outside on a hot windy day, or even inside an apartment with a breeze blowing through, waterborne paints can dry too fast and the roller create a stipple to the surface that can be visible.

Faux finishers have used extenders and scumbles for years. Open time is important to them because if the paints they apply dry too quickly then they may be unable to create the desired effect. These may or may not be suitable for spraying with cup gun systems due to the stiff consistency of some of the products.

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.