Things You'll Need
Liquid measuring cup
Paint stir stick
When you paint with a roller or paintbrush, over-the-counter paint formulas are usually the right consistency for good coverage. However, if you're painting a large surface, like a home's exterior, you often need to thin the paint before loading it into a spray gun. If you thin paint before using airless sprayers and HVLP sprayers, the spray gun will produce a finer mist for even, professional coverage. If your specific spray gun requires 10-percent dilution, you must mix the right substance into your paint for optimal spraying results.
Pour your paint into a bucket. It's easier to mix the paint if you thin it in a bucket rather than adding the thinning agents directly to a loaded paint sprayer. If you're using the entire gallon, just dump it in. For smaller quantities, measure quantities accurately with liquid measuring cups.
Calculate 10 percent of your total paint volume. To find 10 percent of any measurement, just move the decimal one place to the left. To do the math by hand, consider one gallon of paint. One gallon of paint equals 128 liquid ounces. To find 10 percent, multiply 1/10 by 128. The end result is 12.8 liquid ounces.
Measure and add Penetrol if you're using an oil-based paint. Add calculated Floetrol quantities if you're using latex paint. For one gallon of paint, you'll need to measure out 12.8 liquid ounces of Penetrol or Floetrol. Latex paint is water-based, so distilled water also works if you're not concerned with glossy surface adhesion. For a rough surface, watered down latex paint works fine, but a slick surface requires Floetrol.
Stir the paint gently mixture with a stir stick for at least 10 full minutes to ensure even dilution. Avoid stirring vigorously, as this creates unwanted air bubbles in the paint.
Load your paint spray gun according to the manufacturer's instructions and start using your thinned paint.