Junk and oakum

Junk was the name given to old ropes and cables once used on ships. These were cut up and then finely picked into fibres to create oakum. Oakum was then mixed with tar or grease and used as caulking to fill in the gaps between the wooden planks of ships to make them watertight. This website explains how prisoners and slaves were made to do this work. Note the context of where this work was generally done.