HVLP systems are not designed to spray heavier bodied latex paint. However, with some understanding you can successfully do so.
The viscosity (thickness) of latex paint makes it hard for spray guns to fully atomize the paint, meaning that it’s difficult with a lower pressure turbine unit to break the material up into small enough particles to get an ultra smooth surface.
It is essential that you use a good 4 or 5-stage turbine simply for the added pressure and power. The second thing is to use a larger needle/nozzle. A 1.8mm or larger works best. You will also want to use a pressurized cup. The pressurized cup allows the paint to be pushed to the fluid nozzle because of the added pressure behind the paint. If you look at most professional airless paint sprayers designed for latex paint, they are actually pumps, and use no air. Those systems force the fluid thru a small tip which breaks up the paint, but even then, a glass smooth surface is not going to be obtainable.
I have tried over the years to spray a super smooth latex paint, and have done so to a degree, but latex dries fast and even when adding flow out additives such as Floetrol, that super slick buttery feeling finish isn’t going to happen. The only way I have ever been able to achieve a super smooth finish is to use the latex as simply the coloring agent.
I thin the paint anywhere from 5% to 10%, 15% upon occasion and spray several lighter coats by first increasing the pressure and secondly reducing the fluid volume. This may not make sense, but if you think about it, you can’t allow more fluid than the system can atomize. Reducing the fluid really seems to help and I have also found on some occasions I could drop to a smaller needle/nozzle (1.5mm). If we can push the fluid thru a smaller opening, just like the commercial pump sprayers, we increase atomization, which is the key to a smooth finish.
I get numerous emails, about this, especially for kitchen cabinets. I have not found latex paint to be a suitable finish for furniture or cabinetry, in a stand alone situation. On the other hand if you top coat it with a quality water base finish you’re good to go.
I will usually do one or two light coats, just enough to get decent coverage, but again, not trying to get a heavy build, just color. Then I do a good 320 grit scuff sand to smooth. Then I apply a third coat to insure coverage.
When all the paint has thoroughly dried, so that it will powder when I scuff it, I will give it a gentle wipe with some 320 just to maintain smooth. Then I will apply a clear topcoat. Be aware that scuff sanding will appear to lighten or alter the color, but the top coat will bring it right back. The key is to use as little paint as possible and get a smooth, covered color coat, then clear topcoat.
Usually two top coats are needed to get a really smooth surface.
The viscosity, as well as the flow out of the topcoat is what does the trick. Again latex paint is porous, and thick. It’s made to go on heavy and cover quick and dry quick. Top coats are designed to go on thinner and flow out.
I must also state that even if I buy a pigmented topcoat, I always clear coat. It seems anything that has a pigment added to it, stains and mars easier and just doesn’t have that super smooth finish.
Many would argue that the addition of the clear coat isn’t needed on pigmented topcoats, but I assure you if you try it you will be sold. It’s just super nice, and they wipe clean so much easier.
I am, as we speak, completing some cabinets for my daughter, and they are all clear coated. This makes a world of difference.
BTW: I sprayed them all with the ECO 4-stage, Apollo turbine system.