Guitars can take a lot of abuse. But when they crack or split, you need to fix it before it goes any further. Cracks are not uncommon on guitars. Most guitars are made from numerous pieces of wood glued together. Guitar strings are stretched tight, creating an incredible amount of stress on the guitar. If you drop your guitar, or if it has been exposed to a high-moisture environment, the body can crack or split. Repair it with some glue and clamps.
Tape around the crack with masking tape. Place a strip of tape beside the crack on both sides as close as possible without covering it.
Insert the tip of a sharp knife into the crack if possible. Push down on the knife to open the crack as much as possible without making the crack worse.
Place the tip of a glue bottle on the crack. Squeeze the glue bottle hard to inject glue along the length of the crack.
Force the glue deeper into the crack with the tip of your finger. Place clamps on either side of the guitar where needed to get pressure on the crack. Tighten until glue oozes out the crack. Wait 24 hours for the glue to dry.
Remove the clamps and peel off the tape. Use a cloth dampened with furniture polish to remove any residual glue. If there is a fine-white line where the crack was, colour it with a stain-matching coloured marker.
Electric guitars are easy to repair. If your acoustic guitar cracks or splits, there's nothing much you can do about it. Fortunately, acoustic guitars still sound fine with a certain amount of damage.
You can repair almost any crack anywhere on a guitar. But if your neck begins to separate from the body, take it to an experienced luthier or guitar shop for repairs.