Oakum is a fibrous material traditionally made from tarred hemp, jute, or other plant fibers that have been untwisted and loosened from old rope. It is primarily used as a sealing and caulking material in shipbuilding, plumbing, and construction.
Composition and Production
- Historically, oakum was produced by "picking" old rope, a process in which the rope was manually separated into its constituent fibers and then saturated with tar or pitch.
- Modern oakum may incorporate synthetic fibers and adhesives, though natural fiber variants remain in use for heritage restoration projects.
Historical Applications
- Shipbuilding: Oakum was driven into the seams between timber planks of wooden ships using a caulking iron and mallet, then sealed with hot pitch to create a watertight hull.
- Plumbing: In the 19th and early 20th centuries, oakum was packed around pipe joints, especially cast‑iron and lead, before the advent of modern gasket materials.
- Construction: It was employed as a filler in masonry joints and for insulating pipework.
Modern Usage
- While synthetic sealants have largely supplanted oakum in commercial shipbuilding and plumbing, oakum is still used by historic preservationists for the repair of vintage vessels and period‑accurate restorations.
- It also finds niche applications in theatrical set construction and as a fire‑resistant filler in certain specialized engineering contexts.
Etymology
The term “oakum” derives from the Middle English okum or oakum, related to the Old English āc meaning “oak” and cumm meaning “coming together,” reflecting the material’s origin from bundled fibers. Some linguistic analyses suggest a possible connection to the Dutch oekum, but the precise derivation remains uncertain.
Related Materials
- Pitch: A viscous tar-like substance used in conjunction with oakum for sealing.
- Caulking iron: A tool for driving oakum into seams.
- Fiberboard: A modern synthetic alternative to oakum in many sealing applications.
