Tar, what it is and how it is made?
"Stockholm tar", pine tar that is, has been made for thousands of years. The name Stockholm Tar has a centuries old history. Tar was mainly made in Finland (which was a part of Sweden those days) but as it was all sold through Stockholm, the name came and stayed. The poor Swedes had burned most of their forests with their iron industry they came over to the periphery (Finland) and bought our forests in form of tar.
Tar and pine turpentine both come from the pine tree, but in these days they come from totally different process. Pine turpentine comes out as a by-product for paper industry and tar is burned in a tar pit. In the old times it was a different story.
Originally tar was made by damaging the trees over 2-3 years. The lowest part of a pine was barked and only a hand's width of bark was left to keep the tree alive. The tree created a large amount of pitch, but most of it is inside the wood so just collecting the pitch wouldn't have been too productive. After several years of maltreating the tree it was felled. Also the stump was used, since it is the pitchiest part of the tree. Today the damaging is usually not done; they just get less tar for a certain amount of wood. And the forests are full of pitchy stumps to be used for tar after the trees have been harvested.
The wood was chopped to smaller bits and stacked to a tar pit. A tar pit is originally a cone dug out in the ground and covered with watertight (actually tartight) bottom with a hole in the lowest part to collect the tar. A big tar pit could have been 20 meters in diameter (22 yards). I found a site with original pictures about building a tar pit at http://www.paltamo.fi/koulut/kontio/terva/tervahau.htm. The pit was covered with peat and earth and set on fire so that it would burn with the minimum amount of air. If there was too much air all the tar would burn away, with less air it's like distilling solid firewood. Today usually a metal "tar pit" is used, since the airflow is easier to control. A big pit from the old ages could burn for two weeks and produce 5-10000 gallons of tar and large amounts of charcoal, nowdays the amounts are much smaller.
The first fraction coming out of the tar pit is called "tar piss". It contains mostly water and is useless. Next fractions are called "black tar piss" and it's generally "old-fashioned" turpentine, it's just darker as the industrial product today. After that you get tar and finally 'pitch', tar of a consistency of road bitumen.
So tar is in fact liquid smoke, if you think of that. Pitch and turpentine is what keeps a growing tree from rotting alive, so tar is just the "natural rot preservatives" distilled out of the tree. It works brilliantly with pine, which is not an extremely rot resistant tree by its nature.
A fresh product
Tar is a sort of a fresh product. I use about a gallon and a half every year for regular maintenance of three small boats and occasional projects. If it's stored in a plastic container, the lightest fractions go straight through the plastic and your tar can looks like a raisin in the springtime.
The difference on fresh and old tar really can be seen on light wood: fresh tar brings an light amber colour after a few applications and several years old tar would make the surface very dark with the same finish.
Tar can be used old, but it's not the same. My boat was tarred for years with tar that was dug out of 10-year-old tar pit. The tar was full of sand and consistency was closer to pitch but it protected the surface anyway. Ugly it was, but the wood was safe.
Old tar can be thinned down a bit with pine turpentine (some prefer ethanol as a thinner) and linseed oil to get it soak to the wood as fresh tar. And tar is always applied hot, regardless of whether you have thinned it or not.
Always apply it hot
Tar should be applied hot to allow it to soak into wood better. It's fairly thick as is and at least here the weather is still pretty cold when it's time to tar the boats. If you apply it cold, it'll just form a useless surface on the wood. You want to get it inside the wood, or at least the majority of it. Adding linseed oil helps on soaking in and as a bonus the tar doesn't get soft and sticky in the sun. On the other hand too much oil will destroy the best feature of tar: self-repairability. As tar softens in the sun it melts and fixes any cracks or small dents in the coating.
How to heat tar safely? Never leave the tar boiling unattended. If you take it from the stove in time, before it's too hot you are safe. If you allow it to go on a hard, rolling boil, you can get a four feet fire from the kettle and that's a handful to extinguish.
Tar has to come only to a very slight boil. When light brown bubbles start to form on the surface boil it still a few minutes but not more. When it starts to smoke it's a bit too hot. Start applying and when the brush starts feeling sticky against the boat, get back to your stove.
I've used open fire collected from the driftwood on the shore, gas cooker, paraffine cooker (which looked like a giant 2-flame oil lamp), kerosene blowtorch, even a disposable barbeque grill. They all worked although the open fire was a bit too much trouble because the high flames tended to light the tar a bit too often. With other methods I haven't had more than occassional problems.
Where to find tar?
In Finland that's hardly a problem, any hardware store will do. At the Suomenlinna shipyard it is bought by the barrel for the old Baltic Traders. But around the world it's a totally different story. Classic boat mail-order houses have it in ridiculous 1-liter jars with a sad price tag on top. Some people suggested a horse chandlery, since tar is used for treating hoofs.
Hard to tell where they make the tar these days. I have seen tar, which was made with some sort of pyrolysis, not by burning the wood itself. It was horrid stuff, and it smelled like old burnt newspapers. There are not that many places where they are willing to see all the trouble for making proper tar.
As an addition to the "odds and curiosities" list I just had a dish of tar ice cream at the local restaurant. We Finns still have a funny yen for tar, we have tar candies, different kind of tar-flavoured liquors, tar shampoo, and I've even eaten tar-marinated herring. And tarring my boat on the boatyard seems to bring dozens of people there, just smelling the air and smiling.
© Pekka Huhta