Critical Concrete

Linseed & Tung Oil Mix for Wood Protection

Applying a bio-based oil mixture to protect our wood structures is still essential for our work. Our original recipe included coconut oil and needed to be heated in order to combine the various other oils. Therefore we started to experiment with removing the coconut oil which has shown good results on wood. However, the process of heating the oils together with turpentine is time consuming and potentially harmful to the health of the person producing it. Therefore we invested some more time to do research on improving our formula of a wood protection oil-mixture. Our parameters for Critical Concrete are: a simple recipe, a harmless production method as well as cheap, accessible, renewable and raw ingredients to be able to use it for large scale projects.

Research    

DRYING OILS

The most important feature of a coating is that it creates a durable, binding film on the wood. Drying oils such as linseed and tung oil contain a small percentage of saturated acids and a bigger percentage of (tri-)unsaturated acids (table 4) which will help with the polymerization.[1]  During this process the oil reacts with the oxygen in the air where molecules form a polymer chain.[2]  In the end it is a plastic-like coat covering the wood, which reduces the water uptake but still lets the wood be able to breathe.

LINSEED OIL AND TUNG OIL

This table shows that linseed and tung oil therefore have the most appropriate properties, whereas coconut oil as a non-drying oil is not suitable. Linseed oil doesn’t dry as fast as tung oil, but it is still very common in Europe to use linseed oil for wood coatings. It is derived from the flax seeds of the plant linum usitatissimum that grows here naturally. Even though tung oil performs even better it is used less since it’s produced from the seeds of the tree vernica fordii which is originated in China[3] and more expensive. 

Treating wood with linseed and tung oil will slow down biological decay. The coat not only provides a hydrophobic layer which will keep the the percentage of moisture in the wood low and therefore the chance of degradation by fungi[4]  but also protects it against termites. Studies show that tung oil significantly improves protection of wood against termites.[5] 

Thermal or chemical  treatment of the oils will intensify the process of polymerisation which fastens the drying time and increases the water repellency due to higher viscosity.[6]  To make heat-polymerised oils or so called stand oils they are heated to approximately 300°C in an oxygen-free environment. Boiled oils are modified with chemicals such as hydrocarbon solvents and metallic dryers.[7] 

The drying properties of raw tung oil is very good even without a drier, whereas raw linseed oil takes too long to dry after applying. Nevertheless a study shows that mixing both oils in its pure state will provide a  high viscosity to create a hydrophobic layer even without a drying agent.[8] 

Pure tung oil is fairly thick with dark amber yellow aesthetics and a mild smell. It is suggested to thin pure tung oil with at least 30% turpentine for an easy application and deep penetration. This will require multiple layers but will intensify the protective function.[9] There is natural turpentine, an organic solvent, derived from pine resin which is collected by tapping pine trees. It is biodegradable and non-toxic to health if used correctly.[10]  It should not be inhaled, drunk, touched or splashed in the eyes.

THE RECIPE

As mentioned at the beginning we aim for a simple recipe, a harmless production method as well as cheap, accessible, renewable and raw ingredients. That’s why first of all we exclude a chemical-based treatment. The main ingredient for our oil mixture will still be raw linseed oil since it is easily accessible in Europe and relatively cheap in comparison to tung oil. To improve the mixtures characteristics we add a minimum of raw tung oil. Given the fact that we don’t have the resources to heat the oil to 300°C in the absence of oxygen in a non-dangerous atmosphere we won’t modify the oil thermically. The research justifies that both oils can be mixed in its pure form, which will be easier for our preparations when used for bigger projects as well as better for health, safety and environment. Nevertheless we’ll also take advantage of thinning the oil with turpentine which will help the oil to soak deeper into the wood. The combination of both untreated oils and turpentine forms a perfect mixture which is environmentally-friendly, cheap and effective in protecting the wood from water, UV radiation but also termites, fungi and mold.[11] 
Basically we maintain the ingredients and the proportions of the oils since they have been proven to be suitable but we change the amount of turpentine as well as the production method. We choose to use an approximate proportion of 70% oil and 30% turpentine.

Ingredients :

Material RatioGramDensity (gr/l)Milliliter Volume ratio %For 20 litre/ 1 barrel
linseed oil 4.545093048054.510.9L
tung oil110090011012.52.51L
turpentine2.5250860290336.57L

Production method and application

No cooking. Only mixing. Done.

1.Combine both oils and stir until mixed well.
2.Add turpentine, mix well again.
3.Apply one layer per day on clean and sanded wood, repeat 2-3 times.

Note: After every application let it set for 8-12h in the shade. It should also be protected from rain and wind. While preparing the mix, wear a mask – or work in a ventilated environment, gloves and goggles to protect yourself from excessive turpentine exposure (you don’t want a splash of that in the eyes, or the turpentine to excessively dry out your hands) for the whole process to protect yourself. Once the mix is ready, apply in a ventilated space with gloves.

According to Teacă et al [12]“The performance of a coating on a wooden surface in outdoor applications is influenced by the same environmental factors, as well as by the type and intensity of exposure, species, and quality of wood, design and processing of the wood structures, properties of the coating (e.g. glass transition temperature of the coating, thickness, permeability, addition of pigments, dyes or UV absorbers), and its corresponding processing and maintenance, etc. All these factors are acting synergistically on coatings, yielding in weathering which can cause photochemical degradation, cracking, flaking, and erosion of the coating, delamination, as well as color changes with occurrence of discoloration, followed by the wood degradation.”

Finding a critical solution for wood that involves creating a high-performance coating, meeting sustainability requirements, offering weather resistance, and preserving aesthetic appearance is a challenging task. This task cannot be accomplished through a single concept or idea due to the intricate interplay of various interconnected factors that impact coatings in outdoor applications. With this solution we offer one approach that has worked for us, in our conditions, but we encourage potential users to also experiment before applying on a full scale project. We welcome any results or feedback you might have – Feel free to reach out! 

References

1.Bulian, Franco; Graystone, Jon A.: Wood Coatings. Theory and practice, 2009, p. 58-60

2. https://www.nationalgallery.org.uk/paintings/glossary/polymerisation (30.09.2022)

3. https://www.sciencedirect.com/science/article/pii/S0300944020305245 (26.09.2022)

4. http://jultika.oulu.fi/files/isbn9789514287237.pdf (30.09.2022)

5. https://ojs.bilpublishing.com/index.php/jbr/article/download/4793/3833 (26.09.2022)

6.Bulian, Franco; Graystone, Jon A.: Wood Coatings. Theory and practice, 2009, p. 60

7. http://langridgecolours.com/stand-oil/ (26.09.2022) and https://en.wikipedia.org/wiki/Tung_oil (26.09.2022)

8. https://www.sciencedirect.com/science/article/pii/S0300944020305245#bib0075 (03.10.2022)

9. http://www.restaurarconservar.com/Pure-Tung-Oil (26.09.2022)

10.https://webwiser.nlm.nih.gov/substance?substanceId=353&identifier=Turpentine&identifierType=name&menuItemId=75&catId=112

11.Teacă et al. (2019)

12. Ibidem p. 4890

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