Builder Bog is designed to have a very long shelf life and should normally still be usable after even 3 years of storage.

However the components of Builders Bog can separate from heat and vibration, so there is a chance that an older can might have the lightweight dry components floated to the surface with the heavy resinous liquids settled tot eh bottom.

If you bog appears dry and not like a smooth dough consistency try digging to the bottom of the can and if there are liquids there a vigorous stir of the entire contents should get it back to the right consistency and allow it to cure and harden to a wood like result again.