For thinning DiamondFinish Clear, you need a slower evaporating solvent than a traditional paint thinner. When spraying, you can thin DiamondFinish Clear 5-30% with KBS #1 Thinner. If you do not have KBS #1 Thinner and are in a pinch, Xylene can also be used to thin DiamondFinish Clear when spraying.
Please be sure to review the Complete DiamondFinish Clear Directions before starting your project which covers detail instructions for spraying DiamondFinish Clear.