Some fiberglass fillers can be tinted to a variety of colors. If you tint your filler, you can skip painting your repair in many circumstances. Do not run the brush accessory in excess of 15.000 rpm.
Hull blisters are common on boats. With prompt attention they´re not harmful.
Grind out the blister with a 144 high-speed cutter. Recommended speed: 15.000 rpm.
Clean the hole with the 442 carbon steel brush. Wipe away dust with a cloth dipped in paint thinner. Recommended speed: 15.000 rpm.
Finally, fill the hole with fiberglass filler and resin. When dry, scuff the surface before painting.