Once you have determined the optimal film thickness that you would like to use, determine the bar width that you need, depending on the width of the substrate that you will use for the drawdown. So if you have a gap clearance of 6 mils, the theoretical wet film thickness will be approximately 3 mils. As a rule of thumb, the Theoretical Wet Film Thickness of a bar is roughly 50% less than the gap clearance listed for the bar. ASTM D823 contains more information on this subject. Variables such as gap clearance, coating viscosity, percent solids, solvents used, drawdown speed, surface energy and substrate absorptiveness all influence wet film and dry film thickness. Actual wet film thickness can be 40% to 90% less than the gap, and dry film thickness can vary even more.

There are many variables in the drawdown process. It is important to remember that the wet film thickness and dry film thickness of your drawdown will be less than the gap clearance of your applicator. A good tool for this is the Gardco Microm Film Applicator an adjustable thickness applicator that can be used to create varying film thicknesses with very high precision. This can be accomplished by experimenting with various film thicknesses until you determine which film thickness yields the optimal desired product performance. The first step in determining which drawdown bar to use is to determine the optimal film thickness for your application. One of the reasons that high quality and precision Drawdown Bars, (also known as Bird Type Applicators and Doctor Blades) are used in making drawdowns is to ensure that a consistent film thickness is achieved, since most coating properties are thickness dependent.

Color, gloss, opacity, pigment dispersion, wettability, dry weight, drying time, scrub resistance, pigment and dye uniformity, clarity, adhesion, and a host of other properties are measured on the completed drawdowns.

Gardner drawdown bar