Textblocks can be split into two parts, exposing the textblock spine lining, deteoriarated or missing spine lining, or cover strip, and sometimes a security strip.

Sometimes sections or pieces of a book come away or detach themselves from the textblock -- exposing the spine lining (sometimes there is no lining). Sometimes you can see pages coming apart as the spine starts to crack in the middle of a book. These all should be sent to the Preservation Unit for repair.