Can I use boiled linseed oil on wood during the rainy season?
Will it dry? Also: can it be used as it is, without solvents? If the MSDS of a product does not mention drying agents, can I be sure it doesn't contain any?
Using pure, boiled linseed oil is one of the most ecological options for refinishing your deck.
- You can use the oil pure, but there are caveats -- the most important one is a very long drying time, during which the oiled wood must be protected from water.
- Also, the oil can only be applied when the wood is dry. If you apply it over wet wood, or if the wood gets wet before the linseed oil has dried, the bond between oil and wood will be severely compromised and white spots may occur.
- The drying time will vary depending on the wood, the ambient temperature and humidity; expect it to take about four weeks.
Another problem with applying pure linseed oil is that you need to make sure all of the applied oil soaks into the wood, rather than creating an oily film on the surface. Be diligent in wiping off any excess oil about twenty or thirty minutes after application.
Commercial products add a variety of ingredients to improve penetration and drying, and can be used in a wider variety of circumstances.
How successfully the linseed oil penetrates the wood if you do not use solvents depends largely on the wood species; the penetration improvement when using solvents is much more noticeable in hard, dense woods than in soft woods.
Adding a solvent
If you do want to add a chemical solvent, you can add a natural VOC such as natural turpentine.
- While no VOC, natural or artificial, is healthy for you, natural turpentine at least has a very strong smell which alerts you to the offgassing.
- It has also been argued that natural VOCs may be less harmful to humans because the human organism has thousands of years of experience in dealing with the toxin, since you are exposed to low levels of it when walking through a pine forest.
Most commercial products add synthetic solvents in relatively large amounts. Several smaller manufacturers, including the ones mentioned below, also offer high solid or pure solid hard oils or hard wax oils. These contain either little or no solvents, and the higher cost is often offset by a higher yield.
All commercial products contain drying agents.
- Since most manufacturers do not disclose the ingredients, it is unknown which drying agents are employed.
- Bioshield and Unearthed both use the same lead-free drying agents (Zircon Octoat and Cobalt Octoat), which reduces the drying time to one to two days.
The loophole in MSDSs
Manufacturers are not required to list all ingredients in their MSDS.
- Ingredients that make up less than 1%, carcinogens that make up less than 0.1%, or proprietary ingredients/mixtures in any amount do not need to be disclosed.
- The big loophole here is the third one -- manufacturers can blend two toxic ingredients and claim the result is proprietary, relieving them from the requirement to disclose it.
- This severely limits the usefulness of MSDS sheets.
- Also, only ingredients that are known hazards need to be disclosed.
By looking at the maximum percentage listing of an MSDS, and adding up the figures, it is usually apparent that the company is not disclosing all of the ingredients in their product.
I co-own a natural paint and wood finishes company, Unearthed Paints. Besides using the cleanest and most natural recipes available, we disclose all our ingredients, with no exceptions, on the front of every package.
Other small companies do this too, namely Bioshield, and we launched a campaign asking more companies, especially large manufacturers, to follow suit.
Full disclosure is the only way consumers can make informed choices about which products to use.
For more information:
Read our backgrounder "Selecting Healthy and Environmentally Sound Clear Wood Finishes".