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What is caulking?

Caulking is the process of making joints and seals watertight. The name given to a person doing this is a caulker. There are two types of caulker; a wood caulker who caulks joints in wood and an iron caulker who caulks metal joints.

Caulking seat with caulking irons
Caulking seat with caulking irons (PRDHT)

Wood Caulking

In the days of wooden ships and the sailing navy wood caulkers were an important trade and they were also one of the highest paid because they kept the ship afloat.

Wood caulkers caulking a ship ensure the joins between all the planks of wood inside and out are watertight. On a wooden ship caulkers use oakum to seal the joins between the planks. The material to make oakum comes from old hemp ropes. At the start of the twentieth century, prison and workhouse inmates picked apart old hemp ropes to create oakum. Caulkers force oakum between the planks using an iron and special caulking mallet. They then pour pitch along the seam to seal it using a pitch ladle.

Caulker's Ladle
Caulker's Ladle (PRDHT)

Iron Caulkers

The work of the iron caulker was essentially the same as the wood caulker ' namely they made joints and seals watertight. Iron caulkers worked on riveted and later welded ships.

Caulker at Work
Caulker at Work (BDFL)

On riveted ships iron caulkers use a pneumatic gun similar to riveters. The chisel on the end of the gun creates a cutting tool that cuts through steel plate. Caulkers caulked plate edges on ships to make them watertight. To do this caulkers would cut one plate into the other. Chargemen tested their work to ensure that there were no faults in the join. Listen to the oral history extract to find out about testing.

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"Once we caulked it and we finished a job, the charge men then come round with a needle in the end of a pencil, take the lead out and put it and used to run that along the edge of your caulking edge. And if it slid straight along, it was tight, if it jumped up you had to do that bit again because there was a potential leak there. And then after we done all of that, if you're in a tank, you fill the tank with water, and test it, whatever pressure was required, 5, 10, 20 lb per square inch. Once you got the pressure up you went round all again to see if there were any leaks. If there was leaks, you caulked it in until there wasn't."

World War Two

There is an assumption that wood caulking finished when metal ships were introduced. But this is not the case. During the Second World War the Royal Navy arguably had more wooden boats than steel boats. They built motor torpedo boats, motor gun boats and motor mine sweepers. The Dockyards were building masses of these wooden boats which all needed caulking. The wooden decks of frigates continued to need caulking even after the Second World War.


Caulkers together with divers also have an important role maintaining caissons. Caissons seal the entrance to a dock; a watertight seal is essential to keep the dock dry. Caulkers worked on the wooden decks of these caissons. At the beginning of the twentieth century ash was collected from the coal fires which were used for heat, riveters and steam power. It would be set-aside and then when there was a leak on the caissons it would be put into handcarts and the caulkers, or the divers, would then wheel it out to the caisson and pour it down between the caisson and the water. The ash was so light it would sink, and the water would suck in into where the leak was and eventually stop it.

Caisson in number 3 dock
Caisson in number 3 dock (PRDHT)