Pettit 121 Spraying Thinner Pettit 121 Spraying Thinner is a general purpose thinner for thinning spray enamels for easier application. Many paints when stored for some time before use will increase in viscosity and should be thinned with a good thinner for normal spray application. The thinner flashes out rapidly and allows an applicator to apply a light tack coat followed by a double spray coat. Size - Quart. Recommended Use Thin the paint about 10 to 20 and mix thoroughly. For better calculat