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.
Bituminous waterproofing
Roofing felt (similar to tar paper) is the base material used to make roof shingles and roll roofing. Used for decades as waterproof coverings in residential and commercial roofs, these bitumen compositional membranes incorporate two layers. The first underside polymer membrane is used as a solid background, often reinforced with glass fibers. Mineral granules make up the self-protective top layer, with a final bituminous mixture encapsulating them both. Typical uses of felt paper are as an underlay(ment) (sarking) beneath other building materials, particularly roofing and siding materials, and is one type of membrane used in asphalt built up roofing (BUR) systems. The purposes are to "...separate the roof covering from the roof deck...shed water...[and] provide secondary weather protection..." Also, the rapid application of roofing underlay protects the roof deck during construction until the roofing material is applied and is required for roofs required to meet Underwriters Laboratory (UL) fire ratings. The separation of the roof covering from the roof deck protects the roof covering from resins in some sheathing materials and cushions unevenness and old nails and splinters in re-roofing applications. The underlayment also sheds water, which penetrates the roof covering from an ordinary leak, a leak from wind-driven rain or snow, wind damage to the roof covering, or ice dams. However, the application of underlays may increase the roof temperature, which is the leading cause of ageing of asphalt shingles and felt paper wrinkles when it gets wet, which (rarely) shows through asphalt shingles. Not installing an underlay may void the roof covering warranty.