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Best Conditions for Applying Antifouling Bottom Paint

Longer-lasting, more effective paint jobs come to those who wait

For the right time to paint, that is. The right time of year is when you haul the boat out at the end of the season. And the right day is when the temperature, dew point, and relative humidity are at acceptable levels. For best results, a little planning and patience are needed since there's nothing you can do about the weather, especially when painting outside.

The timing of bottom painting also depends on the type of antifouling paint because some paints allow you to wait longer between painting and splashing the boat. Paint at the end of the season, then you don't have to repaint or scuff the surface before splashing.

SPC (self-polishing copolymer) ablative paints such as TotalBoat Argo and TotalBoat Spartan are water-activated and can be painted up to 18 months prior to launch. If launched within this generous window, the paint requires no scuffing to activate the self-polishing properties before splashing the boat.

Other ablative antifouling paints must be launched within a two-week window after bottom painting. If this window is exceeded, you need to scuff the bottom lightly with a Scotch-Brite pad to reactivate the antifouling properties before splashing the boat. The same applies if you remove the boat from the water during the season, and keep the boat out of the water longer than two weeks.

So when can I paint?

Before applying antifouling paint, always check the paint manufacturer's temperature/relative humidity (RH) specifications on the label or technical data sheet for best results. In general, ideal conditions for applying bottom paint include the following:

  • Temperature Ideal temperature of the surface (substrate), air, and coating material should be between 50-90°F.

  • Dew Point and Relative Humidity (RH) The dew point is the temperature at which water vapor condenses. The relative humidity value is how much water vapor is actually in the air compared to how much water vapor the air can maximally hold at any given temperature. When the RH decreases, the dew point decreases, and vice versa.

    It's important to wait until all the dew is gone before you begin applying antifouling paint.

Time of Day is Important Start painting in the morning after the chance for dew formation has passed. Also, avoid painting in direct sunlight because the surface temperature and the air temperature will be too hot and the paint will dry too quickly and will be too hard to apply.

Consider the surface temperature if you're painting outside and the sun will be on one side of your boat in the morning, and on the opposite side in the afternoon. Avoid painting in the late afternoon because of dew formation at dusk.

Allow Time for Drying, Overcoating and Sanding Finally, when you're checking the weather to decide the best time for painting, be sure you have favorable temperature, RH, and dew point conditions to allow sufficient time for drying, overcoating, and sanding. Sanding too soon will clog the sandpaper and overcoating too soon will ruin the effectiveness of the finish. Always check whether the previous coat is adequately dry before sanding or overcoating.

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