Why is tar used to seal cracks?
Oakum
Oakum can be used to seal cast iron pipe drains. After setting the pipes together, workers pack oakum into the joints, then pour molten lead into the joint to create a permanent seal. The oakum swells and seals the joint, the "tar" in the oakum prevents rot, and the lead keeps the joint physically tight. Today, modern methods, such as rubber seals (for example, gaskets or o-rings) are more common.[5]
Grafting wax
Grafting wax is a composition of rosin, beeswax, tallow, and similar materials, used in gluing and sealing the wounds of newly grafted trees or shrubs to protect them from infection. The current formulation typically used in the northwestern portion of the United States for fruit trees, is based on a mixture created by Albert Sak, a German-from-Russia immigrant. The exact original composition is a closely guarded family secret.