By Don Casey
Revised by BoatUS editors in April 2012
If the surface of your boat looks like a cracked eggshell, the gelcoat is suffering from crazing (sometimes called alligatoring). The easiest repair method is to sand the surface heavily and roll on two coats of epoxy primer followed by two coats of two-part linear polyurethane. The epoxy fills and seals the cracks, and the polyurethane restores the color and gloss.
If you don't want to use paint, you can grind away most of the crazed gelcoat and replace it with a fresh application of color-matching gelcoat paste. What won't work is to "paint" over the crazing with new gelcoat. The gelcoat will bridge the cracks rather than filling them, and the crazing will soon return.
By the way, localized crazing (as opposed to all over the boat) is almost always due to flexing of the underlying laminate. In this case, you must stiffen the affected area before you can successfully repair the crazing.