Oakum is a tarred fiber that has a long and distinguished history for use in shipbuilding and the repair of various sea-going vessels. Essentially, it is a blend of fibers that are coated with tar and can be used to fill in small cracks in various types of structures. In centuries past, tarred oakum was often prepared by persons serving time in prisons, as well as people who were forced to labor in workhouses in order to work off outstanding debts.
There is more than one form of oakum available for use. In addition to the tarred version that is made by using the jute or hemp fibers of old ropes, there is also white oakum. This is created with the use of hemp fibers that have not been woven into ropes and is not impregnated with the pine tar that was used in many instances to make the fibers resistant to water and the elements.
In usage, oakum was extremely helpful around the shipyard. The substance served as an ideal packing material that could be used as a means of caulking or sealing the small spaces between the joints of ships made completely of wood. As ships that were primarily constructed of metal became more common, oakum was still used as a means to provide caulking and stability to the wooden deck planking that often was used to outfit the metal body of the ship.
Over time, oakum also found use in various projects on land as well. Before the advent of plastics, it was often used to provide caulking and sealing around the joints on drainpipes and other forms of piping in the home. With a relatively low cost, it was possible to use the material for patching drainpipes over time, thus delaying the need to replace the entire length of pipe. This was usually accomplished by packing the joint with the oakum, then applying a small amount of molten lead to the area. The lead would cause the fibers to swell and create an effective seal around the joint.
While the use of oakum is rare today, the material is still utilized by shipbuilders who seek to create a vessel that is a replica of the sailing vessels of years gone by. However, it normally serves more of a decorative use today rather than a practical one.