Wood drying starts immediately after cutting, the fibre ends, i.e. the cut area, being the place where the water comes out fastest. This is the area most prone to cracking, which can sometimes lead to significant wood loss. This is why wood splitting is a 'hot' topic of interest to all those who work with solid wood. This is because wood can crack during drying, during cutting, during transport or storage, and sometimes even during the work or use of the resulting objects. Solutions have always been sought to prevent cracking and reduce losses. One of the most commonly used solutions is sealing wood with paraffin. Let's see how it protects the wood and how it should be used for maximum efficiency.
What causes wood to crack
Cracking is caused by stresses that occur in the wood as a result of the drying process. The more water the wood is filled with, the greater the stresses and the greater the likelihood of cracking. Also, the harder the wood, the higher the stresses will be. To avoid very high stresses, trees are felled outside the growing season, the best months being December and January when it is frosty. In February, the new growing season already starts, especially lately when the average monthly temperatures have risen.
The water comes out fastest where it went in. By cutting, the fibres through which the water has entered the wood and circulates inside the tree are severed. It is through these fibre ends that water tends to escape and so they must be closed.
Moisture exchange with the environment continues as before pruning, i.e. at the area of contact with the outside (bark). The drying process starts from the outside and goes inside the log. This is how the difference in humidity between the inside and the outside is created. To restore the balance (a process that occurs naturally) water migrates from the inside to the outside. If the water on the outside of the log is leaving quickly and in large quantities (peeled wood + high outside temperature), the water inside migrates outwards in large quantities to restore the balance. And so other tensions arise.
This is why wood is sprinkled during the drying process in the kilns - so that there are no large differences in moisture content between the outside and inside of the wood to be dried. It is also the reason why natural drying is done without protecting the wood from rain. It is important, however, that it is protected from the sun, which is why the stacks for natural drying are covered at the top.
How to slow down the water outflow from wood
I think it's already clear that in order not to have cracks in the wood we need to slow down the water outflow, thus reducing stresses. That is why it is recommended that:
- the severed area of the trunk (fibre ends) is sealed, i.e. covered with a substance that prevents or reduces the rapid escape of water. The sooner the coating is applied after cutting, the lower the risk of cracking;
- as far as possible not to remove the bark from the trunk. This acts as a protection that reduces water leakage. Unfortunately sometimes this is not possible because of pests (curries, other insects) that may be under the bark and can get into the wood;
- cut the wood as quickly as possible into "slices" of the desired thickness. This reduces stress and the risk of splitting. Take care that the wood shrinks through drying so the planks should be cut thicker.
The water continues to flow until it reaches equilibrium humiditywhich in our geographical area is 8-12% for wood used indoors and 14-18% for wood used outdoors. Throughout this period the risk of cracking persists and the most exposed area is at the ends of planks.
If cracks appear before the fibre ends are treated, it is recommended to first remove that portion and then seal the cut. Once started, the crack will advance even if the area is protected with various solutions. It is the "weak link" that will give way first when stresses develop within the wood.
Using paraffin to prevent wood from cracking
Paraffin, in solid or emulsion form, is the most suitable option for sealing the fibre ends. It is applied both to the ends of logs immediately after cutting and to the ends of planks, even if they have a lower risk of splitting.
Sometimes the trunk slicing option cannot be chosen or the planks have to be cut to a very large thickness. This is the case with wood from which vases, bowls or other such objects are made by turning. Thick wood is needed for these. This wood needs to be protected during drying, and paraffin coating is a very good solution.
Paraffin wax is non-toxic and can be easily removed by washing with soap and water. However, if you are one of those who make items for use in the kitchen, you will need special 'food safe' paraffin wax. This is what fruit and vegetable exporters use to protect goods from dehydration and during transport.
Solid paraffin must be heated before application to become liquid. This is the only way it can act as a fibre plug. Liquid paraffin is applied to the ends of logs or planks with a brush, paintbrush or a tracer. Two coats are recommended for best protection. The second coat should only be applied after the first is completely dry and hardened.
Paraffin emulsion - the simplest and most effective protection solution
Paraffin emulsion is much simpler to use and is very suitable for large pieces, freshly cut logs, large companies dealing with industrial wood cutting and drying. It does not need to be heated before use and can be applied with a brush or spray gun.
Such a protection solution is TISZAWAX,distributed on the Romanian market by Szolvegy from Targu Mures. It is an aqueous paraffin dispersion with a milky appearance that can be coloured at the customer's request. A good solution for the protection of logs and wood blanks, wood to be transported (by sea, by train, in containers or by truck) or wood to be stored for a longer period.
Dispersion advantage TISZAWAX is that it no longer needs to be heated before application, as it is liquid. Another advantage is that it can be applied with a spray gun. This greatly reduces working time and the tiny droplets cover the fibre ends or areas to be protected very well and effectively. Consumption is 0.7 kg/m³.
Wood has several stages of life and knows how to assert itself in each of them. Those who work with solid wood know that it can't be compared to plastic or any other 'good and obedient' material. You have to make friends with wood and slowly convince it of what you want to do. I admire Japanese precisely because of this connection they establish with wood. You won't be able to cut the wood today and work it tomorrow and expect everything to be fine. You have to give it time to get used to its new life and in my opinion this time is the drying time.
I wish you good luck and patience!
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I intend to make some pallets for setting beehives on the hearth and in the pastoral. The system is widely practiced in Canadian beekeeping. I have cut the oak, cut it to size and am going to assemble the components. But the wood is still green although the oak was felled now in December after the oak has come out. Surely there will be tension in the material after assembly, so I'm thinking of letting it dry naturally until spring.Would it help to boil it in paraffin the way hives made of dried fir are boiled? About what paraffin consumption would that be? What approximate moisture content is in oak in my situation? I suspect at least as much paraffin would be consumed as would replace the water in the wood.