If you’re painting outside, consider positioning the boat in a north-south orientation, so you can work on the shaded west side in the morning, and the shaded east side in the afternoon. No matter what application method you use, be sure you have adequate lighting. Also, to minimize dust, dampen the floor or ground before you start painting.

Topside paints can be thinned with solvent to change viscosity and improve consistency, making them flow more easily for spraying. Thinners, or reducers come in several different types: some are better for warmer (slow reducer) or cooler (fast reducer) conditions; some are necessary for either brush/roll or spray application. Due to the extreme toxicity of sprayed two-part polyurethanes containing isocyanates, we do not recommend DIY spray application.

Thin one-part polyurethane according to the manufacturer’s directions using the specified thinner in the amount suggested according to conditions such as air/hull temperature and humidity. The goal is to thin the paint so it can be applied consistently. Typical thinning for spraying polyurethane paint is anywhere from 5-20%, depending on the paint. Be careful not to over-thin the paint or it will sag when sprayed on the hull, and will lessen gloss retention after curing.

Before you begin spraying, ensure that your work area is well-ventilated, and that you’re wearing appropriate, high-quality personal protective gear, such as a paint suit with hood, eye protection, a NIOSH-approved chemical organic vapor cartridge-type respirator or fresh supplied air, and gloves.

Results depend on the type of sprayer, and attention to the paint manufacturer’s recommendations for spray tip type and size, pressure, flow, and angle of spray.

Proper spray technique usually focuses on three things: aiming the spray pattern, your triggering technique, and your overlapping technique.

• Aiming the spray pattern: Hold the gun upright at a consistent distance from the surface while spraying and move your arm while keeping the gun pointed straight at the target surface for a smooth, even finish. If, instead, you keep your arm still and move the gun in a fan pattern from side to side, the finish will be uneven.
• Pressing and releasing the spray trigger: Start moving the gun before you press the trigger, and continue your arm motion after releasing the trigger to avoid creating added thickness at the beginning and end of each stroke.
• Proper overlapping technique: To apply the paint evenly, each time you make a pass to spray, overlap by 50%. Point the spray tip at the bottom edge of the previous spray pass to ensure efficient overlap.

Common problems encountered while spraying include runs and sags, pin-holing, solvent pop, fish eyes, blistering, mottling, and orange peel. Practice your technique on something other than your hull, such as a primed piece of plywood. Sometimes the problem requires nothing more than applying the material in lighter coats, speeding up the gun movement, or holding the gun closer or further from the surface while spraying. Consult the manufacturer of your spray equipment or the paint manufacturer for specific usage and troubleshooting instructions.
 

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