To repair a split fingernail, clean it, apply nail glue, buff the nail, and clean the surrounding skin with acetone. The required supplies include acetone, cotton swabs, nail glue, an orange stick and cotton balls.
Dampen a cotton ball with acetone nail polish remover, and rub it over the nail. Brush a small amount of clear nail glue over the crack and the surrounding portion of the nail. Wait 10 seconds, and then use a manicure stick to smooth the glue over the crack. Press the flat portion of the stick tip over the crack, hold it there for one or two minutes, and then release the pressure.
When the nail glue is completely dry, gently buff its surface with a buffing bar. Stop buffing as soon as the surface of the glue is smooth and blends in with the rest of the nail. Dip a cotton swab in nail polish remover, and use it to remove any glue that dripped onto your skin or cuticle.
If it is impossible to repair a split nail immediately, immobilizing the nail prevents the crack from growing. The easiest and most effective way to immobilize the crack is to cover the nail with a small piece of clear tape, according to Black Cat Nails. Adhesive bandages also work, but contain strong adhesives that may tear the nail during removal.