Oakum

Top Definition

OAKUM was once used to seal the cracks between the planks of wooden hulled sailing ships. It is made by impregnating hemp fiber with tar or creosote that binds the hemp together and makes it moisture resistant. Over time, it was adopted to seal air cracks around windows and doors, plug holes that rodents and bats won't chew through and close the openings in walls and floors where cast iron plumbing pipes passes through. Today, it is a relic that is still used for the same purposes but electricians use it to seal holes around electrical piping where the code doesn't require that a firestop be used. When it gets wet, it expands 10 times its dry size. The NUPAK brand uses Bentonite as the impregnating compound. Although not commonly used, it is still stocked in 5lb boxes composed of 2' strands.