Famous Case #2: Caulking HMS Victory

Modern sealants are convenient to use but are no match for traditional techniques when it comes to historical ships.

HMS Victory, Nelson's flag ship during the battle of Trafalgar on 21 October 1805, is on permanent display in Portsmouth, UK.
Needless to say, not only it had to be extensively repaired after the battle and its successive uses before retirement, but the 251-year old ship must undergo regular repairs to withstand rain, dry rot, death watch beetle and visitor's feet.
For the last fifteen years, modern marine caulking sealants were used on the deck, but it was subsequently found that they could not withstand the natural movement of wood, and soon water leaks appeared.

The gaps between the deck planks that must be made water tight are about 6mm wide.

In a recent renovation campaign, the modern sealant was removed manually and replaced by oakum and pitch. Oakum is a loose hemp or jute fiber.Previously, oakum used to be made in workhouses, prisons, and by children from old ropes and cordages. Nowadays, a machine is used for that purpose. The caulking is done by pressing the oakum in the gaps and pouring hot tar pitch derived from pine sap or from petroleum residues. A tool called a caulking iron is used to manually pack the caulk. The operation can be viewed at https://vimeo.com/47098266.

Pine tar pitch is made by carbonizing pine wood or bark in anoxic conditions, allowing the low-boiling components to volatilize. Process is similar to Birch Tar Glue.