Many materials that can be applied with a brush need to be thinned down for paint spraying. The thickness of the material is known as the “viscosity” and by adding thinning material such as water or thinners lowers the viscosity enabling the material to be atomised.

First the type of thinning agent must be determined which most manufacturers will include on the material container. In some cases the manufacture will state that no thinning agent is required or will provide the ratio of thinning agent to material. An excellent guideline is to use the same material that is recommended to clean up. For example if the can says clean the brush in water then use water as a thinning agent. If the can suggest the brush is to be cleaned with mineral spirits than use this material as a thinning agent. Using measuring cup and a separate mixing vessel is desirable, as this will allow subsequent mixtures to be almost identical to the initial mixture. Mixing the material in a separate vessel ensures the correct viscosity before being poured into the spray gun pot.


Using too much thinner will cause a number of problems. The material being applied to the surface may run, drip or sag. Even if this does not occur more coats may need to be applied to achieve the desired coverage and finish. Also because the coats will dry much quicker pinprick bubbles may form as the excessive amount of thinners try to escape. On the other hand not enough thinners will result in either a blocked spray gun or a very coarse or lumpy surface. 

When pouring the mixture into the spray pot it is vital that the pot is clean, dry and free from any dust as all these impurities will be transferred onto the spray surface. Paint strainers can also be used to remove any impurities that may have gathered during the mixing process. There are many to choose from, however the most popular and widely available are nylon mesh or paper funnels.