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Tar Based Boat Finish

Various tar and oil based mixtures have been used to protect the wood and rope of ships. This BOAT SOUP is still in use for reproduction vessels and for small dinghies. Some Scandinavian boats are still being protected this way.

If you are making a reproduction ship, it is highly likely that the original was finished with at least some tar and oil. If you visit a wooden boat and see a dark stain on the ropes and decks, you are looking at a tar finish.

The tar finish is a penetrating coating and will sometimes go quite deep. Most modern varnishes are top coats only and if damaged allow water in.

Even though the finish is not absolutely waterproof in thinner layers it allows the wood to dry easily if it's exposed to water. This helps prevent pockets of moisture building up. Modern varnishes are more waterproof because they form a solid film barrier but if water gets under the finish it does not dry so easily and pockets of rot can develop.

Tar has antibacterial and anti fungal properties that protects the wood or fibre it coats.

Where was the tar finish used

tarred linesstandig rigging

Various lines and ropes were tarred. In fact the fibers were coated even before being spun into rope so there was some protection when it was made. Standing Rigging which did not have to bend or move was heavily tarred. Other lines which needed to go through blocks or needed to be coiled were more lightly protected.

These impressive lines are from the Sorlandet. Because they don't need to move or go around any block, they are very thoroughly and thickly tarred.

tar kilnboat deck

Any wooden part of a ship was a candidate for tarring and the hull and decks received regular and generous coatings of boat soup.

Decks were a good candidate for tarring and made the wood much darker. It also gave the boat it's distinctive smell. This was the first thing I noticed when I went near the Viking reproduction ship, the Draken Harald Harfagre

Viking ship stern Viking ship standing

Tar was used in the making of the Draken Harald Harfagre. It helped glue and waterproof the various seams of the hull planks which were riveted together, it also coated the inside and outside of the hull.

British sailors were called "TARS" or "JACK TAR" because one of their constant jobs was to apply the protective coating on their ship. They carried the pungent smell of tar and no doubt many stains from the coating. It is said that they put it on their hair to keep it out of trouble and not get caught in the rigging. This is hearsay, I have not found a good reference for the hair. Tar coating was also used to waterproof protective clothing including overcoats.

Tarps were often tarred to protect them and make them waterproof.

Tar finishes were also used to protect against tropical wood borer worms. For example the Endeavour (of Captain Cook fame) had a layer of tarred felt nailed to its hull to protect the wood. Later ships would be covered with copper and then brass to protect them.

Oakum, tarred hemp fiber, has long been in use to caulk between hull boards to make the hulls water tight. Oakum was made from old ropes that had to be laboriously taken apart and untangled. This was a job often done by prisoners and work house inmates. Any sailor could also be set to picking oakum in his spare time.

Because of its anti-bacterial and anti-fungal properties, it's been used for years for various skin and scalp ailments and for helping horse hooves and feet heal from infection. I've seen farmers use a tar dressing on animal wounds. It also has the advantage of keeping flies away from a wound. The tar coating helps discourage other animals from biting the area. Pigs will bite a wounded pig and tar coating takes away the blood smell.

If you have an old house with cast iron plumbing you might have oakum in the joints of the pipe. It was hammered in the joint and lead was poured over the joint to help make it water tight.

What is tar?

Like all terms which were coined a long time ago the definition is not exact.

tar kilnImage compliments of By Svenboatbuilder via Wikimedia Commons

Tar is the result of destructive distillation (pyrolysis) of various resinous woods and roots. The tar contains various organic materials possibly including turpentine and various resins. A favoured wood was Pine varieties. In early days the wood was processed in specially constructed kilns. Later tar was made from heated steel retorts.

Stockholm tar is the preferred material for marine use and is generally made by the more laborious kiln method.

In more modern times, tar is a by product of the making of charcoal. It is also distilled from petroleum products. It can be produced from many materials as well.

There are many grades of tar available and characteristics vary depending on the method of manufacturing and the other components present. Tar can be very light coloured or almost golden and quite runny. It can also be almost black and thick. The dark colour is caused by carbon being incorporated during the distillation/burning process. Darker tar provides better UV protection but stains everything.

Wikipedia link to rope tarring.

Tarring Recipes

Tar is usually not applied alone. Rather it is mixed with at least oil and often a dryer to make it flow on better and dry faster.

Link to "The real stuff" tar as well as other products for traditional boats

Unless you use specifically light stockholm tar you will be making anything you paint quite dark. Tar does stain and sort of softens if it's really hot.

Most recipes suggest similar amounts of tar, boiled linseed oil and turpentine. Several like to add some leftover varnish. Many like to have a bit of japan drier to help the mixture set faster.

Typical Recipes

Japan drier needs to be fresh. It is less effective if it is too old. If you add more pine tar, it will take longer to dry and be darker.

Although linseed oil is the usual oil suggested, any drying oil can be used, or a mixture.

Drying oils are oils that will eventually dry, cure, and harden when exposed to air.

There are a great number of oils which can, and have been used, such as linseed oil, tung oil, fish oils, and walnut oil.

Because materials differ quite a lot I would make a test batch and test it before using it on a critical surface.

Canadian supplier for stockholm tar

Small Print

I got interested in tar finishes after visiting tall ships and Viking reproduction ship. This web page is the result of notes I took while researching tar finishes. I don't claim to be an expert in anything. Many coatings and paints are toxic or dangerous if used improperly. Many finishes have flammable solvents and components. As they dry, paints and varnishes often give off heat so any rag should be disposed of carefully and not left where the accumulation of heat can occur. Before using any product READ the label and take the warnings seriously.

email me if you find mistakes, I'll fix them and we'll all benefit: Christine