The short answer
A VOC figure is a number of grams of solvent per litre of product. In Great Britain the law caps it at 400 or 500 grams per litre for the subcategories a hardwax oil sits in, and that cap has to be printed on the tin next to the actual content. Several of the best known hardwax oils are at or near the cap. Oslek LED Hardwax Oil contains 6.4 grams per litre, because it hardens under light rather than by evaporating.
Almost every finish on the market now says low VOC somewhere on the tin. The phrase is not regulated, so on its own it tells you nothing. The number next to it does.
What a VOC actually is
A volatile organic compound is a carbon-based substance that evaporates at room temperature. In a wood finish it is the solvent: the part that makes the oil thin enough to spread and to soak into the timber, and that then leaves.
It is worth being clear that the solvent is not an impurity somebody forgot to take out. In an air-cured oil it is the mechanism. The finish hardens because the solvent goes. That is why the smell is strongest while the floor is drying, why the room needs ventilating, and why a finish that has stopped smelling has usually stopped curing as well.
Why light-cured oils are different
An LED-cured oil does not harden by losing anything. A 395nm LED lamp triggers the molecules in the coating to link to each other, and the film goes from liquid to solid in the time it takes to pass the lamp over it. Nothing has to evaporate for that to happen, so the formulation does not need to carry a solvent load in the first place.
That is the whole reason the figure is 6.4 rather than 500. It is not a cleaner version of the same chemistry. It is a different way of getting hard.
What the law allows
Great Britain caps the VOC content of decorative coatings. The limits sit in Schedule 2 of the Volatile Organic Compounds in Paints, Varnishes and Vehicle Refinishing Products Regulations 2012, and they are set per subcategory of product, for the coating as it is ready to use.
Three of those subcategories could apply to a hardwax oil, depending on how the maker classifies it. Osmo quote a maximum of 500 grams per litre, which tells you they are working to the one-pack performance coating line.
This is the context that makes a number mean something. A finish quoting 500 grams per litre is not breaking any rules. It is sitting on the legal ceiling. Roughly half the weight of that tin is designed to end up in the air of the room you are standing in.
And this is also why the phrase low VOC is close to useless on its own. It is not defined anywhere in the regulations. A product at 390 grams per litre can call itself low VOC and be within the law in doing so, because it is lower than the 400 ceiling that applies to it.
The number is already in your hand
Here is the part most people do not know. Regulation 5(1) requires the label to state three things: the subcategory of the product, the limit value for that subcategory in grams per litre, and the maximum VOC content of the product in its ready to use condition.
So you do not have to take anyone’s word for any of this, including ours. The number is on the tin by law.
The trap is that the limit and the content sit next to each other, and the limit is the larger, rounder, more official looking number. It is not the one you want. The limit is what the law allows. The content is what is in the tin.
Where the finishes actually sit
Every figure below is published by the maker. We have put the legal ceiling on the same chart so the scale is honest.
Two things worth saying about this chart rather than leaving you to notice them.
Rubio Monocoat beat us. They publish zero grams per litre against our 6.4. On this one measure they win outright, and we have written that up properly on the Rubio comparison.
Osmo and Fiddes publish a maximum, not a measurement. Up to 500 grams per litre is a ceiling the product sits under, somewhere. Treatex publish 492, which reads like a measured figure. We would rather compare measured numbers with measured numbers, and where a maker only gives a maximum we say so instead of pretending otherwise.
The four product comparison pages work through each of these finishes properly, because VOC is one measure among several and cure time, coat count and coverage all move the answer.
What this number does not tell you
We would rather say this than have you find out afterwards
- Content is not the same as emissions. A VOC content figure describes the wet product in the tin. What a finished floor gives off into a room over days and weeks is a different measurement, taken in a test chamber to EN 16516 and reported in micrograms per cubic metre. The two are related, but they are not interchangeable, and a content figure cannot be converted into an emissions figure.
- We have not had chamber emissions testing done. So we quote the content figure, because that is the test that exists. If you are specifying to a scheme that asks for chamber data, ask us and we will tell you plainly that we do not have it yet rather than send you something that looks close enough.
- A low VOC finish is not automatically the right finish. It still has to be hard enough, look right, and be repairable. The comparison pages cover where other products are the better buy, and on the Rubio page that is the headline.
- VOC content says nothing about what the cured film contains. That is a separate question with a separate test, and we have covered it on is hardwax oil safe for children and pets.
Frequently asked questions
What does 6.4 g/L actually mean?
It means that one litre of Oslek LED Hardwax Oil, ready to use, contains 6.4 grams of volatile organic compounds. It is the same figure as 99.4 percent VOC free, stated the other way round. For comparison, the legal ceiling in Great Britain for a solvent-borne one-pack performance coating is 500 grams per litre, and several well-known hardwax oils sit at or near it.
Is there a legal limit on VOC in wood finishes in the UK?
Yes. The Volatile Organic Compounds in Paints, Varnishes and Vehicle Refinishing Products Regulations 2012 set a maximum VOC content for each subcategory of coating. For the subcategories a hardwax oil could sit in, the solvent-borne maximum is 400 or 500 grams per litre and the water-borne maximum is 130 or 140. Those are ceilings, not targets, and a product can be fully legal and still be most of the way to the ceiling.
Does the tin have to tell me the VOC content?
Yes. Regulation 5(1) requires the label to state the subcategory, the limit value for that subcategory in grams per litre, and the maximum VOC content of the product in its ready to use condition. So the number is already in your hand. The thing to watch is that the limit and the content sit next to each other on the label, and it is the content you want.
Why do hardwax oils have VOC in them at all?
Because most of them dry by evaporation. The solvent makes the oil thin enough to spread and to penetrate, then leaves, and what it leaves behind hardens. The solvent is not a contaminant, it is the mechanism. That is why removing it is not a matter of reformulating slightly, and why a genuinely low figure usually means the curing mechanism itself is different.
Why is a light-cured oil different?
An LED-cured oil hardens because the LED light triggers the molecules in it to link together, not because something evaporates away. The hardening does not depend on anything leaving the film, so there is no reason for the formulation to carry a solvent load in the first place. That is where the 6.4 comes from.
Is low VOC the same as low emissions?
No, and anyone telling you it is has skipped a step. VOC content is a figure for the wet product in the tin. Emissions are what a finished surface releases into a room over time, which is measured in a test chamber to EN 16516 and reported in micrograms per cubic metre. The two are related but they are not the same measurement. We publish the content figure because that is the test that has been done.
The easiest way to judge a finish is to cure one yourself.
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