caulk, to

caulk, to, to drive, with a caulking iron, oakum or rope fibre into the seams of a ship's wooden deck or sides in order to render them impervious to water. After the oakum was driven in hard, the gap between the planks was filled with hot pitch or some other composition to prevent the oakum from rotting through contact with water. On yachts and small boats caulking cotton would be used.

The Chinese used quite different, but equally efficient, materials. The 13th-century explorer Marco Polo noted that Chinese junks were caulked inside and out with ‘lime, and hemp chopped small, and they pound it all together, mixed with an oil from a tree’. The result was sticky and when smeared onto the hulls held like birdlime. Other travellers reported that a putty-like composition of sifted lime and tung oil was used, and in some places the ashes of oyster shells replaced the lime. In Cambodia during the same era a mixture of fish oil and lime was used; in the Persian Gulf fish oil mixed with oakum; on the Somali coast whale oil and lime; while the ocean-going canoes of the Pacific islanders were caulked with coconut fibre and adhesive breadfruit sap. See also chinse.