How to Fix a broken Surfboard Fin
If the fin is not completely broken out of the board, it will need to be cut out.
A small angle grinder or coarse sanding pad can be used to grind away the broken glass and rovings.
Keeping the sanding disc level in the bottom of the board, undercut the fin.
Cut away broken glass and rovings until fin breaks free.
Try not to cut the fin and alter its shape and height.
Sand the glass around the fin area slowly. Try not to get the glass too hot as this will cause it to delaminate.
If water has seeped into the area, it will need to be completely dried out before proceeding.
Sand the glass around the fin so it feathers out about 3 inches.
Take the fin and sand each side to it’s original shape.
If there is foam missing or broken leaving a hole.
Make a Qcell slurry and fill the hole. When hard sand smooth and flat for the fin to stick to.
Fin position may need to be remarked. If centre fin, measure where it was before removing. If it is a side fin, match the angle layout and tow in to the opposite fin . Tow in is where the front edge of the fin is pointing to the nose. E.g. 2” either side of the stringer at the tip.
Sand broken and excess glass from the fin to bring it back to original shape.
To stick the fin in position use a large alligator clip to steady it in position and paint a fillet of catalyzed resin around the base.
Alternatively I use masking tape. A piece of tape about as long as your arm. Stick to rail then top tip of fin and to other rail. Straighten fin by lifting and resticking tape until lined up. Eye from the nose, if the stringer and the fin look in one straight line or the angles are the same that’s lined up.
When the resin around the fin is hard and the fin is stuck on, gently remove tape or clamp. If you bump the fin at this stage it may break off.
Rovings: are continuous strands of fiberglass which form a rope like cord. We use rovings to form a larger fillet joining the base of the fin to the board. They usually come in a large roll that seems to last forever. However you can by shorter cut lengths from a material supplier who has cut them into a kit form.
Alternatively you can make your own by pulling individual strands from a square of fiberglass cloth. Cut a square of cloth a couple of inches bigger than the base of the fin. Pull each strand out and lay side by side to form a cord about the thickness of a average little finger. This should give you enough rovings for one side of the fin. Repeat for the other side.
Hold rovings together and trim the ends neatly to the correct length. Aprox 1” either side of front and rear of fin.
Place the rovings neatly on the board away from the area to be laminated. Cut four more pieces of glass, 2 for each side of the fin. The bottom layer slightly larger than the top to allow the feathering out.
These pieces should be large enough to laminate halfway up the fin and aproximately3”-4” out from the base on the board.
Place these pieces neatly aside so they are easy to pick up when required.
In a container make a slow mix of laminating resin. Approximately 1 cup. Catalyze at 1%
With a 1” brush paint the resin around and up the fin where the glass will lay. Picking up the rovings place them each side of the fin base. It is easier to pick them up if you keep at least one hand free of sticky resin. Dip the brush in the resin and paint one end of the rovings so they wet out and stick to the board. Put the brush on the end of the rovings once until that end has stuck to board . then lift the brush off. This will help in stopping them from moving and ending up in a mess. Then wet out the rest of the rovings until the whiteness disappears. Work the rovings over to make a fillet at the base of the fin. Put the brush down and use your fingers to squeeze out air bubbles. Shape the fillet into the corner of the fin base. Repeat other side of fin. Pick up the pieces of cloth you have cut to lay-up the sides. Place them in position and carefully paint resin on and up the fin. Just wet the cloth out , don’t drown it. The cloth should extend past the ends of the rovings front and back and half way up the fin and 3-4” out from base on board.
Put the container and brush down and use your thumb and fingers to squeeze out bubbles and excess resin. Smooth the resin out so that the glass is not floating and there are no pools of resin.
The neater you laminate the easier to sand smooth.
Allow to gel then trim any excess over hang front and back of fin with a sharp blade. If it hardens before you get a chance to trim it then you just have to sand a bit more.
Mix filler resin , catalyze and paint another coat over the laminated cloth. This resin makes it wax up and harden so it will sand. Laminating resin stays sticky and won’t sand.
Leave the filler coat to harden say 4 hours or next day. Then sand around the base of the fin and smooth and flatten the area so it blends into the original surface of the board. If you have stands that you can put the board up on a rail it makes it easier to sand up the fin. Be very careful when sanding the fin. You have to hold the sander so as not to catch the sharp back edge of the fin. But you must foil the glass into the shape of the fin without removing it completely. This is a delicate job and takes some skill. An orbital sander is safer but takes a bit longer. When smooth and finished sanded you can now either gloss coat and polish or in the case of most modern short boards spray clear finish or just wet rub into the rest of board.
How to fix a Fin Plug broken out or cracked
To remove old plug I use a diamond hole saw and drill.
I have a clamp guide the same size as the plug and hole saw.
Clamping over the plug I hole saw down slowly to the depth of the base of the plug. The plug may break free but if not remove the hole saw. Then with a screw driver or tab of the fin twist the plug until it breaks free. Clean and dry the plug hole and trim any broken cloth away. Check hole for depth by placing a new plug into it . The lugs on the plug should be flush with the board.
Take the new plug and place on a fin or setting jig. Cut a piece of cloth 1’ x 2” This will lay in the hole for strength.
Mix up filler resin , enough to fill the hole. Add some white pigment and catalyze slow. If you don’t have white pigment white acrylic paint will do. Don’t use to much paint as it will stop the mix going hard.
Three quarters fill the hole with resin. Lay the piece of cloth over the hole and push the fin with plug attached into the hole. When there is only one plug being replaced the other fin plug will line the fin up automatically. If you are replacing both plugs you will have to tape the fin in position and line up as in fin replacement chapter. When the plug is set and hardened it can be sanded flat to the board surface. Screw the Allen screws in before sanding.