Seal: 1. Apply sanding sealer to balsa fins. 2. Sand smooth after drying. CA Glue: 1. Add thin CA glue for strength. 2. Allow thorough drying. Reinforce: 1. Apply fiberglass or carbon fiber cloth. 2. Use epoxy resin to bond. 3. Let it cure. Finish: 1. Sand for smoothness. 2. Optionally, apply a clear coat or paint.