oakum

thumb|Oakum and tools for caulking thumb|Hemp thumb|Prisoners picking oakum at Coldbath Fields Prison in London

Oakum is a preparation of tarred fibers used to seal gaps. Its traditional application was in shipbuilding for caulking or packing the joints of timbers in wooden vessels and the deck planking of iron and steel ships. Oakum was also used in plumbing for sealing joints in cast iron pipe, and in log cabins for chinking. In shipbuilding it was forced into the seams using a hammer and a caulking iron, then sealed into place with hot pitch.