## Wednesday, April 5, 2017

### The Math of Mixing Car Paint.

If you ever had your car repainted or needed touching up, the painter has had to mix paint for the car.  According to a chart produced by Sherwin-Williams automotive finishes, most paint follow certain ratios of thinner to paint.

Mixing ratios are often given in parts or percentages.  If given in parts, the basic measurement has to be used consistently throughout the mixing process.  For instance, if using a 4:2:1 ratio, it means 4 parts of the base product, 2 parts thinner and 1 part hardener.  It might be 4cups, 2 cups, and 1 cup or 4 tbsp, 2tbsp, and 1 tbsp.

If its expressed in percentages such as 25%, the percentage needs to be changed to a fractional equivalent.  25% is 1/4 which is the ratio needed to mix paint.  1/4 means 1 part thinner or reducer to 4 parts paint base.

In addition, the type of paint often determines the ratios used.  For instance, if it is a single stage paint which is glossy and durable and you only need to put on a few layers to be done.  The usual ratio is 8/1/1, or 8 parts paint, 1 part reducer/thinner, and 1 part hardener.

On the other hand if you use a two stage paint which starts with a base coat paint with a ratio of  1 to 1 or 1 part paint to 1 part reducer.  For a clear coat, the ratio is either 4/1 or 2/1 with say 4 parts clear coat to one part hardener.

Furthermore, the type of paint used will determine if you only mix paint and thinner, or whether hardener is needed.  For instance, the solvent based metal paints is thinned down using a 2 to 1 ratio of paint to thinner.  No hardener is needed  while the two pack acrylic requires a 2:1:10  the 10 being a 10 percent mix of hardener.

So much real math using ratios in a real life setting.  It wouldn't be hard to create an exercise requiring students to plan to repaint their own car.

Let me know what you think.