No, Spartan does not require thinning, but adding a maximum of 5-10% (6-12 oz. per gallon) of TotalBoat Special Brushing Thinner 100 for brush/roller application, or up to 10% (12 ounces of thinner per gallon) of TotalBoat Spray Thinner 101 for spray applications, can help create the smoothest possible finish.