There are many reasons why glue might not work as it's supposed to: The surfaces you are trying to glue are dirty or greasy, thus preventing the glue from properly bonding to the surfaces. Make sure the items are clean from visible dirt and debris. PVA and solvent glues work by sinking into the surfaces of the articles being glued and forming a physical bond to lock the pieces together. You might be using the wrong glue for the surfaces you are gluing; check the glue label to see what surfaces it's formulated to adhere to. The glue might need to be applied differently. Make sure to read all instructions before using.