The wooden tables and chairs on the family terrace are given a coat of oil in early spring and another one in autumn, which is a regular routine for many families. The oil brush is dipped generously, and after a few rounds, the wood becomes shiny and smooth, with water droplets unable to stay on its surface, rolling into individual beads, which is pleasing to the eye. The wooden doors and windows in my hometown are also treated in this way every few years. Over time, many people have gained confidence that applying a coat of oil can effectively prevent wood from decaying.
This method really works on the terrace. The tables and chairs are placed under the eaves of the house, so they won't get drenched in heavy rain. The oil applied forms a layer of film on the surface of the wood, protecting the outermost layer. The oil can't be stored in the grain of the wood, so even if you apply it ten times, it only soaks the outermost grain. By applying it twice a year, the wood can be kept clean and white. Even if you are lazy and don't apply it one year, and the film fades, it's still not too late to sand it down again and apply oil. Anyway, the wood can be moved, and people can stay nearby to reapply oil whenever the film becomes thin.
However, there is an unavoidable premise for this trick: the wood must be movable. The task of applying oil is just about the surface layer. The brush goes back and forth a few times, and the oil stops at the shallow layer of the wood. It can't penetrate further. The wood looks solid, but in fact, it is very hollow inside, filled with tiny pores that are invisible to the naked eye, like a bundle of thin straws tied together. The oil goes a little way along these fine cracks and then runs out of steam. When the oiled wood is cut open, the outer ring is dark in color, but the inside remains the original appearance of the wood.
The patio tables and chairs are not afraid of this. They can be moved and repaired every year. If the oil is thin, just brush it twice more. The repair is a matter of diligence. The sleepers do not have this treatment. Once they are laid, the oiling must be done ahead of time. A sleeper is laid on the road and doesn't move for decades. No one takes it down to brush oil. The track patrolmen walk over it and don't worry about it lacking oil one day. The oil on it must be applied in one go before laying.
The process in the factory is different from painting at home. The wood doesn't go through a brush, but rather through a tank. The wood that enters the tank is already dry, leaving space in its pores. Once the tank door is closed, air is first pumped out to clear the air from the wood's pores, leaving room for the oil. Then, oil is added and pressurized, pushing the entire tank of oil into the wood. Efforts are made from all directions, ensuring that every thin straw gets its turn. The oil follows the pores deep into the wood, reaching places that the brush could never reach in a lifetime. Once the pressure is removed, the oil remains, becoming a part of the wood. The wood coming out of the tank is heavy, and one can tell by feeling it that it has been fully saturated.
The difference between this and applying oil is, to put it bluntly, the difference between permeation and pushing. Permeation is the wood's own absorption, and how deeply it absorbs depends on fate. Pushing, on the other hand, is different. It's about applying force from the outside, and where the oil goes, that's where it's effective. The same piece of pine wood, with oil floating on the surface, and oil settling inside, are two different things. This kind of strength can't be given by a brush.
In daily life, we can actually observe this difference. When we nourish our kitchen cutting boards with oil, the oil disappears after being wiped on for a while. We have to feed it over and over again, hoping that the oil will slowly penetrate into the board. However, if we soak the cutting board in warm oil, the oil disappears much faster. This is already a step towards "pushing", just not as far as the jar.
Where wood stands guard outdoors for a long time, the path taken is always the one of oiling. Along the railway, sleepers are lined up one after another for miles. In mining tracks, ore cars roll over the sleepers repeatedly. Once these woods are laid, there's no such thing as "moving them back for repairs". The oil must be infused into the wood in advance, and it stays there for decades. The annual oiling of patio tables and chairs relies on diligence. The sleepers are fully oiled at once, relying on that oil can. No one is superior to others; it's just a matter of whether you can move them or not.
To prevent wood from decaying, we need to use brushes on the terrace and cans on the railway. The sleeper is too long to reach with a brush.
