Surfing School - Repairing - Broken Boards
This is probably the toughest repair job there is. You can fix the board, but it will never be as strong or light as it was initially. For best results, you will need two 8" long and 1/4 to 3/8 inch diameter dowels, a hand drill, and a sander. Using the hand drill (the old type) carefully drill two 4 inch deep holes in one end of the break, parallel to and about 1 inch on either side of the stringer. Place the two dowels in these holes, lay the two board halves on top of a table, and carefully align the half pieces together to determine where to drill the holes in the second board half. The holes should match up height wise as well as offset from the stringer.
Use the sander to sand down slightly the glass in a 5 inch ring around each half at the broken end. Be very careful not to sand through the outer glass. Tape off the un-sanded area for two or three inches past the strip.
Put newspaper on the table or flat surface you plan to use (not on the floor). Using laminating resin with a small amount of hardener, place the dowels in first, making sure the tow edges of the board break are exactly even with the board bottom, and straight against the flat surface. Tack the two pieces together by painting a layer of resin set to go off quick (hot) on each broken end, then pushing the two pieces together. The resin used for the dowels, which shouldn't be hard yet, can work by carefully adding a little more hardener. Use a few small wood blocks to adjust the two pieces so the rails align correctly, then tape the two pieces together until they are set. We suggest you make the wood blocks fit first before you try to laminate the board pieces.
The broken board should be glassed in two sessions after tacking, first the deck with the bottom flat and together, and then the bottom. When the tacking resin hardens, apply the top cloth. Squeegee the cloth around the rail to just underneath the rail line, and then trim the excess cloth just when it starts to cure with a razor blade. After curing, the bottom can be laminated in the same manner.
From this point on, the fill coat, sanding, and final gloss is similar to what is identified earlier. We use one layer of 6 oz. cloth on both sides, but some people use 4 oz. If you skip the dowels, we strongly recommend 6 oz. cloth or you run the risk of having the board break in your face when paddling through a larger wave.