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How to Thin Waterbased Automotive Paint

Updated July 20, 2017

Growing environmental concerns have got everyone looking for more environmentally friendly ways of doing things. The way we paint our cars is no exception. The heavy solvent-based paints that have dominated the automotive refinishing world are now being replaced with earth-friendly water-based varieties. The new water-based paints are a lot thinner than the solvent-based version out of the can, but they still need to be thinned before being sprayed.

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  1. Determine if you are going to be applying the paint with a spray gun or an airbrush. The mixing ratios are different for the two applications.

  2. Pour a mixture of nine parts paint to one part reducer in the mixing cup for use with a spray gun or a mixture of three parts paint to one part reducer for use with an airbrush.

  3. Stir the liquid with the paint stick until it has been thoroughly mixed. At this point, the paint has been successfully thinned and is ready to be sprayed.

  4. Tip

    While the general guidelines are the same for most water-based paints, make sure that you check the manufacture's instructions for the paint that you are using prior to mixing.


    Always wear a breathing respirator that is approved for the use with automotive paint while working with paint.

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Things You'll Need

  • Water-based automotive paint
  • Water-based reducer compatible with the paint
  • Plastic mixing cup with 1:10 and 1:4 ratio graduations
  • Paint stick
  • Breathing respirator

About the Author

Based in Wisconsin, Scott Furniss has been writing professionally since 1997. While finding a home as a technical writer in the pharmaceutical industry, he has earned a place on the Manpower Hall of Fame and is a recipient of the Tiffany Award of Excellence. Furniss is pursuing a Bachelor of Science in business from the University of Wisconsin-Parkside.

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