How to Mix Auto Paint With the Correct Ratio

by Paul Miceli

Mixing auto paints to the correct ratio is a relatively straightforward procedure and can be carried out in two different ways. Modern materials require the use of paint mixing stick to produce diluted quantities by volume. However, some types of auto paint, such as synthetics, still require mixing. Correct mixing allows for easier application and effective paint flow. In turn, this helps paint to atomize correctly to produce a superior finish with minimal "orange peel"-type textures, strong metallic content and excellent levels of adhesion.

Mixing Stick Method

Refer to the technical data sheet supplied with the paint to establish the correct mixing ratio. Most modern two-pack systems and solvent-based metallic colors are mixed at a ratio of 2:1 with a compatible hardener or thinner. Water-based colors are usually mixed at a ratio of 10:1 with a compatible water-based thinner.

Take a clean mixing pot and place a paint mixing stick with the correct ratio markings inside it. The stick should rest upright against the walls of the pot. Stir the paint for several minutes so that it is thoroughly mixed. Establish how much paint will be required. Paint mixing sticks are marked in measurements of one-tenth of a liter so if you require 300ml of material, you will need to pour in enough paint until it reaches the number 3 on the left-hand side of the mixing stick.

Store the paint away and remove the lid from a tin of compatible hardener. The middle section of the paint mixing stick will be marked out with equivalent measurements to those used on the left-hand side of the stick. If you have poured to the number 3 on the left hand side, pour in enough hardener until it reaches the number three on the middle of the paint mixing stick.

Replace the lid on the hardener and take a tin of compatible thinners. The right-hand side of the stick will be marked out with percentage figures in 10% increments. Most modern materials only require 10% of compatible thinners so add enough material until it reaches the appropriate line.

Store the thinners away safely and stir the paint, hardener and thinners together using the same paint mixing stick. The material can now be added to the spray gun and applied to the vehicle.

Viscosity Cup Method

Refer to the technical data sheet and view the recommended viscosity times. A viscosity cup holds a standard measurement of thinned paint and the time represents how long it should take for thinned material to drain through the cup. This is usually presented as range. For example, the viscosity time may be in the range of 15 to 18 seconds.

Activate the paint by adding a quantity of hardener. See the technical data sheet to establish the ratio and use a marked paint mixing stick to help you create a base material before the viscosity check begins. Ensure that you have a stopwatch ready and that the timer is set on zero.

Fully immerse the viscosity cup into the activated paint, ensuring the removable cap on the cup is in place. Wear latex gloves to stop paint getting onto the skin. Lift the viscosity cup out of the paint and allow excess material to drop back into the tin.

Remove the cap on the viscosity cup and, at the same time, activate the stopwatch. You may require a second person to make this easier. Allow all of the material to flow through the hole of the viscosity cup until it is empty. Deactivate the stop watch as the last of the paint falls through.

Read the time on the stopwatch. If it falls within the recommended range, the paint is ready to use. If the time recorded is below the recommended range, the mixed paint is too thin and more base color should be added. If the time is above the recommended range, the paint is too thick and more thinner should be added. Continue to carry out viscosity checks until the correct times are achieved.

Items you will need

About the Author

Based in the United Kingdom, Paul Miceli has been a professional writer since 2006. He has been published online by Ideate Media and Promiga and has a proven track record of producing informational articles and sales copy. Miceli is educated to U.K. "A-level" standard, continues to work as a paint sprayer and has more than 25 years of automotive body repair experience.

Photo Credits

  • photo_camera paint image by Chad McDermott from