Wood putty lids can often become damaged after they have been opened and closed a few times. This allows air to enter the can and dry out the contents. To help prevent some of the damage caused by hammering the lid back in place try pressing the lid on by hand and then turning the can over and hitting the top on a flat surface such as a workbench or concrete floor. The lid should snap in place with one motion. Painters use a variation of this technique by pressing the lid onto the paint can and then stomping it in place with their shoe.