I want to protect the gate with linseed oil. How do I make the wood absorb as much as possible? Do I use boiled linseed oil or spice oil? If I stain it, does the fibre still show?

What you will find out

It feels like spring is here. More and more questions are being asked about exterior finishes, gazebos, fences, pergolas or garden furniture. The preference is for linseed oil, but there are many unknowns about how to use it, its properties and resistance. I am glad to discover, however, the desire for information in order to do things as correctly as possible. The idea for the article started with the finishing of a solid wood gate for which I received a very elaborate posting. A series of finishes were proposed, starting from wood burning and covering with linseed oil to various oil-based lazes or water, accompanied by many questions about linseed oil in particular. We have selected the most frequently asked questions in order to give the necessary answers and explanations.

How do I make wood absorb more oil?

Protection with oils comes from the fact that they penetrate into the wood and protect it from the inside against moisture. The advantage of linseed oil is that it has a smaller molecule than other oils (tung oilfor example), making it easier and deeper into the wood. But sometimes it needs a little help. A first way is dilution. Use white spirit, petrosine (kerosene) or, for those who prefer natural and healthy solutions, turpentine - extracted from pine resin - or citrus oil. It is recommended to dilute the first 2 coats, then reduce the amount of thinner added. Another method to decrease the dilution is heating. This makes the oil more fluid without the inconvenience of extra thinner.

A very good way to increase absorption is wood sanding. The surface of the wood is sanded with 150 or 180 grit sandpaper and the fiber is cut, opening several paths of absorption. Sanding can also be done 2-3 times before applying oil coats. Fine sanding paper is not used because it has no power to break the wood fiber and the resulting fine dust can close the fibers, thus blocking absorption.

How do I know the wood has absorbed enough?

The oil is applied in excess, allowed to absorb for 30-45 minutes, then wiped off. Linseed oil does not react with oxygen in the air and does not form a film. Any excess left un wiped off becomes sticky, very unpleasant to the touch and in appearance. When the first coats are applied, the wood will absorb all the excess and it will not be necessary to wipe off the excess. When, after 3-4 coats applied with sanding, the oil remains unabsorbed after the 45 minutes, the wood has reached its maximum. It will absorb again after a period of use when weathering and mechanical action will remove some of the absorbed oil.

Why boil linseed oil?

To dry faster. Natural, unprocessed linseed oil dries very slowly. It can take from a week to a month before the surface of the wood no longer has the appearance and behavior of wet. To speed up the process, linseed oil is boiled. In the past, lead compounds were added to this process to increase the polymerization capacity of the oil, resulting in faster drying. Now lead-based compounds are no longer used because they are dangerous (lead is a heavy metal). The oil is boiled for several hours at very high temperatures and in the absence of oxygen. The result is a natural compound that is more viscous than the original product, darker in color and dries much faster.

What is Sicativated Linseed Oil?

It is an oil whose drying time is reduced by chemical compounds called silicates. Sicatives are generally cobalt compounds. The oil undergoes a thermal process in which these silicates are added to greatly reduce the drying time.

Why is colored linseed oil recommended?

Linseed oil, unlike tung oil, is not resistant to UV radiation. It protects wood against moisture, but cannot protect it against the sun. That's why wood treated with plain, uncolored oil can change color over time, turning a grayish-gray that is typical of wood that has been left unprotected outdoors. A pigment is added to linseed oil to make it resistant to the sun's rays. This is basically the recipe for oil-based outdoor varnishes. The amount is not large - around 5% - so the oil remains transparent, or more precisely semi-transparent. The pigments are meant to deflect the sun's rays so they don't end up damaging the wood.

Can oiled wood be coated with varnish or paint?

Oiled wood can only be coated with oil-based paints or alkyd varnishes and paints. A film-forming product will prolong the life of the finish as it will be an extra water barrier. But the wood can also be left with just oil varnish (lightly colored oil with pigments) provided the refinishing is done more often. The life of protected objects is greatly increased if water does not puddle on the surface and if they are not standing directly in the rain, protected with awnings or eaves.

How resistant is linseed oil on the outside? After how long does re-oiling take and how do I know it's time?

Linseed oil is not very hard-wearing on the outside. Its thin molecule and the fact that it doesn't form a film allows water to wash it off more easily than tung oil, for example. This is why linseed oil is used in outdoor products mixed with other natural or synthetic oils. Its resistance over time depends very much on how much it rains in the area, how well the object is protected, how well the water drains away and how well the natural ventilation that dries the water is done. Linseed oil does not protect the wood against the growth of mold and therefore great care must be taken when standing water.

Sometimes, if the conditions are difficult, re-welding should be done at 6 months. But usually it is done every 1-2 years. The sign that maintenance is needed is the dry appearance of the wood, without that oily sheen that remains immediately after finishing. If it is not re-oiled immediately, the wood begins to turn gray and mildew can appear, blackening it in places.

WARNING! During the drying process, the oil reacts with oxygen in the air, the reaction releasing heat. This can lead to auto-combustion, i.e. ignition of waste and oil-soaked rags used in the application. It is recommended that all such scraps, utensils or rags used should be placed in an empty paint can in which water has been put and the can covered with a lid. The process of ignition is accelerated by the sun's rays (the sun gets on these oil residues).

I hope you find this information helpful. If you have any additions, clarifications or questions, please leave them below in the space provided. I will certainly reply.