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Traditional Maritime Skills :: Caulking 2

Caulking

Introduction

The barque schooner ‘Tres Hombres’ is a sail cargo ship with a wooden hull and superstructure. The ‘Tres Hombres’ is kept in service as a sail cargo ship by three captains and their crew, who aim to demonstrate with this ship that sustainable cargo transport by sea is possible without using fossil fuels.

The barque schooner was built in 1942 as an outpost ship (navy cutter) and has since been adapted into a sea-worthy sail cargo ship. The ship was officially certified as a sail cargo ship without engine in 2009. The ship is regularly maintained, which is generally undertaken by the crew and the passengers during the voyage and during maritime events or when in dock.

At the Meerman Yard in Arnemuiden students are taught on a practice board how to caulk. This board resembles a section of a ship’s hull, with joints between the strakes. Historische Scheepswerf C.A. Meerman in Arnemuiden is the oldest yard in Zeeland and one of the oldest shipyards still in operation in Europe. The ships that are maintained here belong to the Stichting Behoud Hoogaars, an organisation dedicated to retaining sail-powered fishing boats from Zeeland as part of our sailing heritage.

Both the practice board in Arnemuiden and the maintenance being undertaken on the Tres Hombres are shown in the training photographs for this skill.

Use

Caulking – also spelled calking – is the process of sealing the joints between timber planks, for example those on the hull or decks. The purpose of caulking is to make the timber surface watertight.

Materials and Tools

Hemp
Originating from the cannabis plant, is used because of the long structure of its fibres. Hemp is supplied in large coils. For caulking above water and for narrow joints caulking cotton is also used because cotton is thinner and is easier to work.

Pitch
Is used to fill up the sealed joints and for smoothing. These days Tixopal is mainly used rather than pitch. Tixopal is a synthetic sealant which can be applied using a sealant gun.

Caulking mallet
Is a wooden mallet with sound boxes. The mallet has a head on both sides of the handle and is designed in such a way that you can apply a great deal of force on the point that you hit, without having to hit very hard or having to use a very heavy hammer. The purpose of the sound boxes is to allow you to hear whether the hemp has been knocked sufficiently hard into the joint.

Raking iron
Is a piece of steel with a curved point which is used to scrape the joint clean before hemp is inserted.

Caulking iron
Is a steel chisel which is used for hammering the hemp into the joints between the wooden planks. There are various thicknesses and widths of caulking irons, and there are straight and curved caulking irons for accessing difficult corners.

Procedure

Caulking is undertaken when building, maintaining and repairing wooden ships or on ships with a wooden deck. Caulking step-by-step:

  • Using the raking iron scrape out (as necessary) the part of the joint that is to be re-caulked.

  • Take a 1 to 2 metre length of hemp from the coil. Roll the strand of fibres tighter together on a flat surface by rolling up one side of the strand each time and winding the strand around your hand.

  • Push one end of the strand into the joint at the location at which you want to start and push the other end loosely into the joint quite a bit further along (if the strand hangs down loose it will unroll again).

  • Using the caulking mallet and a narrow caulking iron hammer the first end securely into the joint. Now make a loop in the strand varying from a few centimetres to a decimetre. Using the caulking mallet and the caulking iron hammer the strand beyond the loop securely into the joint next to the first length, make another loop, after the second loop hammer the strand again into the joint, right next to the hammered-in length, and so on. This creates a joint with loops that protrude outside of the joint. Continue doing this until the full length of the joint has been filled.

  • Return to the start of the joint and now hammer the loops securely into the joint. To do this, place all of the loops on one side and hammer all of the material into the joint using the caulking mallet and a narrow caulking iron.

  • Once all of the hemp is on the joint, continue hammering with the caulking mallet and using increasing widths of caulking irons until you hear from the sound from the caulking mallet sound box that the hemp has been hammered in so tight that it approximates the hardness of wood. (It is now also very difficult to remove the hemp from the joint.)

  • In the past pitch was used to finish off the hemp-filled joint. These days the joints are usually finished off smooth using Tixopal, which is available in a sealant tube. This is applied evenly using a sealant gun. The excess is removed using a filler knife with a flowing movement. Pick up any excess using a piece of kitchen roll for example, because the sealant is extremely sticky.

  • After this finishing operation the wood can be varnished, painted or tarred.
 
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Tools Required

  • Caulking mallet
  • Raking iron
  • Caulking iron

Materials Required

  • Hemp
  • Pitch

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