Depends if its into the fiberglass or not, depth and width take into account. I'd say resin over it...but that may not hold up in time, also where is the crack actually at? Ive done fiberglass work..but not on surfboards. You might look into a patch to make sure it doesn't get worse. Someone who does this more often might shed some light on this.
Usually in surfboards it's only the hotcoat/gloss coat, so you can sand them out and re-hotcoat. They happen when the board over flexes, and are found more on boards with too much resin in the hotcoat or multiple hot/gloss coats. Sometimes they don't go all the way through and won't leak for a long time, but sometimes they do, and will turn brown along the cracks.
If fracture is the correct identification( which normally results in penetration to the cloth ) it should be cut out and replaced. If its more of a slight crack then do as LBCrew suggests with the hotcoat. If you post a picture of the issue you can be given better advice on a fix.
Last edited by wave1rider65; May 16, 2012 at 12:17 PM.
Don't worry about cracks unless it's through to the glass. But, if you're gonna fix it do as LBCrew suggests and sand out the fractures and re-hotcoat. Most likely it's a polyester resin glass job if it has flex cracks so use solarez with surfacing wax, brush it on, put it in the sun for 3 minutes to cure, then sand with 100 grit, 150, 220 until you're satisfied with the shine.
~Brian www.greenlightsurfsupply.com Shape Your Surfing Experience