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.
Rebar spacer
Concrete spacers and bar supports are made of the same material as the poured concrete, so thermal expansion and contraction are equal. And because they are the same material, the concrete and spacers will bond. No gaps!
Concrete spacers and bar supports help maintain material integrity and uniformity of the concrete, and provide a cover over the reinforcement that protects against corrosion.