This particular instructable will show you how to fix a nasty delamination/split. One of the fins of my new [sic] surfboard must have gotten whacked at some point, since the fiberglass had actually cracked open and had some uberdelamination going on. After five minutes of work and some drying time, it was good as new!
Step 1: What's Wrong?
The other problem is that the fiberglass is delaminating, or separating from the foam core. Even if I were to re-attach the fiberglass, it still wouldn't have much rigidity, since a couple layers of fiberglass alone isn't very strong. You have to glue it to something to really take advantage of the modern marvel that is composite construction
Step 2: Get Da Tools
Next, go to your local surf shop and get yourself some epoxy. I really recommend the surf shop, since some epoxies will tear through foam like crap through a goose, and your local surf experts will know what epoxy is appropriate for you. You'll also need some fiberglass cloth (you can get it at a surf shop or any hardware store), some disposable gloves. a couple C-clamps, some scrap wood and a little tupperware to mix the epoxy in.
Step 3: Fix the Delamination
First off, tear off a bit of sandpaper and slide it under the delamination. Rasp it all around and get rid of any burrs in the foam or the fiberglass.
Next, mix up some of your epoxy. Mix it really well--I usually mix it for a minute straight. Popsicle sticks are great for mixing, or you can do what I do and just use a piece of cardboard. Get a thin piece of cardboard or over thin, stiff material gooped up with epoxy and slide it under the fiberglass. Move it all around in there. If you press on the fiberglass, you should be able to see where the epoxy is through the glass. Keep adding epoxy until you have the entire area covered. Make sure there's no bubbles under there.
Step 4: The Clamps!
Keep it clamped down and let it dry overnight. While you're waiting listen to some Handsome Boy Modeling School. Oh, Nathaniel Merriweather! You rogue!
(you might notice that there's no fin in the picture for this step. I didn't take a picture of fixing this particular delamination, but here I'm fixing another similar delamination on the same surfboard.
Step 5: Eyes Glassing Over
Now, you're gonna put a piece of fiberglass over the crack to patch it up. Take your fiberglass cloth and some scissors you're not too attached to and cut up a patch that'll fit over the crack with maybe an inch of extra on all sides.
Now, either with an electric sander (a palm sander, not a belt sander) or just some good old-fashioned sandpaper and elbow grease, smooth out the area around the crack. Fiberglass sticks really well to really smooth surfaces, and it loses lots of strength any time it loses contact with whatever's under it.
Once you're happy with your sandjob, lay the fiberglass over the crack and mix up some epoxy. Dribble a little bit on top of the fiberglass and then using a piece of cardboard, spread the epoxy out over the fiberglass. When the fiberglass is 'wet', it should be see-through. You don't want to drench the thing in epoxy, but make sure you get the entire piece wet, and then squeejee off any excess.
Cool. Let it dry and come back the next day.
Step 6: Done!