Pickguards sometimes break away from the top of guitars.  This is caused by the material itself shrinking over time.  If your lucky it doesn’t split the top when it shrinks.  The pictures on this page are of a guitar that has been cracked by the dreaded lifting pickguard.

The crack is glued (preferably with hide glue) and cleats are also glued on the inside of the guitar.  This prevents the crack from opening or spreading any further.

 

Next the pickguard is cut out using a slightly larger template. This enables

the new one to overlap the original footprint and the crack.  On some guitars (older Martins)  the original pickguard was lacquered after it was installed so I like to spray a few coats on the pickguard before gluing it to the guitar.