Wood is a noble and living material that continues to react to different external agents once it is cut from the tree. For example, excess moisture can lead to yellowish-brown stains appearing on the surface caused by the tannins in the wood. In this post you will learn what are wood tannins and how to solve their effects.
The tannins are the cause of these unsightly dark spots that can appear on wooden floors and furniture. As in other aspects of daily life, knowing your enemy will help you fight it.
What are wood tannins?
Tannins are polyphenolic compounds produced by plants, especially woody ones. Its main function is to protect plants against the wounds they suffer and from external attacks since their ingestion can be toxic for microorganisms and herbivores.
The woods richest in tannins are usually cedar, mahogany and fir, although it can also be produced in the knots of some types of pine. Tannins are drawn to the surface of the wood by moisture (wood is also said to bleed or “bleed”), leaving an unsightly brown stain that can seep through layers of paint (most noticeable when have used light colors). Sometimes tannin stains can appear in woods that do not contain this type of substance, since they can be transmitted by contact from one wood to another.
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According to their typology, wood can be classified into:
- Coniferous, resinous or soft: its structure is porous and the most common species are Scots pine, Oregon pine and fir. They are rich in resins, essential oils and tannins. This type of wood is usually used to make interior furniture.
- Leafy, woody or hard: their structure is more complex than that of the woody ones and they are not very porous. The most common species are oak, chestnut, eucalyptus, cedar, beech and walnut, with oak, chestnut and cedar being the richest in tannins. Normally this type of wood is used in construction, as well as for furniture and interior flooring.
- tropical: their internal structure is similar to that of the woody ones although they are normally darker than these, they are also not very porous. The most common species are iroko, rosewood, teak or ipe. They are very sensitive to the sun’s rays, they are not impregnable, very resistant and rich in tannins. This type of wood is usually used in facades, pool decks, terraces and gardens.
Main causes of the appearance of wood tannins
The main cause of tannins bleeding to the outside is humidity and this can occur due to:
- The wood has been treated when it contained a humidity level higher than 15%.
- The wood has not been sanded and sealed properly.
- Areas in permanent contact with moisture have not been protected.
In addition, the stains produced by the tannins of the wood can also appear due to:
- Protective anti-tannin products have not been applied.
- Some fittings can favor the appearance of tannins, it is better to use them made of stainless steel.
Image via Dezeen
How to solve the effects of tannins on wood?
Although the best way to prevent these unsightly spots from occurring is prevention, there are also solutions when they do appear.
First of all, it will be necessary locate where the excess moisture is coming from and correct it, repairing any cracks or knots you let through. In addition, if the humidity is produced by condensation, the installation of ventilation grills, extractors or dehumidifiers must be considered.
In the event that the stain has penetrated the paint or is visible under the protector or varnish, it will have to be stripped and removed before repainting or protecting the wood. For this it is used oxalic acid and then the wood is cleaned with pressurized water, allowing at least 48 hours to pass for it to dry completely before applying any treatment.
For stop the bleeding or exudation of tannins from the wood It will be necessary to use specialized products that block moisture and prevent damage and cracks that can occur in it. It is also very important that the wood is completely protected, since if spaces are left untreated, it can leak.
In the event that the wood is going to be painted, it is recommended to apply one or two layers of previous primer, It is very important that the drying times between coats are respected.. It is also advisable not to use water-based paint on wood that has already suffered the appearance of tannins or is more exposed to its effects.
Finally, we must bear in mind that when choosing the most suitable product to protect or paint wood, we must be guided by the climate, the hardness and type of wood and the tone of the finish, never by the price.
Summarizing…
In short, wood, like all living beings (even after being felled), defends itself against external aggression. In cases of humidity, it sends its battalion of tannins so that they can defend it from the action of fungi and microorganisms.
The best way for wood not to feel threatened is to protect it properly and avoid risky situations, as well as “injuries” that may occur on its surface.
If the tannins have entered into action causing the unsightly dark spots, it will be necessary to strip to leave the wood bare, remove the stains with oxalic acid and clean with a pressurized water. All this work is useless if the wood is not properly protected to prevent it from feeling threatened again.
Finally, the tannins of the wood can pass into the wine, providing it with particular characteristics of flavor and aroma, which is why oak barrels and other woods are used for aging.
Did you know that they are wood tannins? Have you ever suffered its effects? If so, it has a solution, and now you also know the keys so that the wood of your platform or furniture is not affected by the stains caused by tannins.
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