What does a hardener do in wood oil? When is 2K application worthwhile, and what should you keep in mind?
Wood oil can cure without a hardener, too. So why add one? Because additional cross-linking can make a difference in curing, durability, and water repellency.
The OLI NATURA® Hardener is a reactive hardener additive for selected OLI NATURA® wood oils. It enables additional chemical cross-linking. The result: the oil can cure faster, and the surface becomes usable sooner and more durable.
How does wood oil cure?
Drying vegetable oils such as linseed oil and tung oil react with oxygen in the air. Their molecules bond together to form a solid network. This process is called oxidative cross-linking or oxidative polymerization .
Liquid oil becomes a cross-linked solid. With impregnating oils, this cross-linking takes place in the wood. This fixes the absorbed oil in the wood.
Important to know: Dry does not mean fully cured. Even when an oiled surface already feels dry, cross-linking continues in the wood.
What does an additional hardener do?
In addition to oxidative drying, OLI NATURA® Hardener enables additional chemical cross-linking reactions.
To illustrate: You can think of cross-linking like a woven fabric. The more tightly the threads are connected, the stronger the fabric becomes.
Similarly, additional chemical cross-linking can make the cured oil system more durable.
Four benefits at a glance:
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Ready to use sooner: Curing is accelerated. The surface reaches its full durability sooner.
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Greater durability: The cured oil system becomes more resistant to everyday wear and tear.
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Improved water repellency: Additional cross-linking can significantly improve water resistance.
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Stronger pigment binding: With suitable colored oils, resistance to color abrasion can increase.
Important: The hardener does not replace oxidative drying. It supplements it with additional chemical cross-linking.
1K or 2K - what’s the difference?
1K means: The wood oil cures without an additional hardener.
2K means: A suitable hardener is mixed into the approved wood oil immediately before application.
| 1K - without hardener | 2K - with hardener |
|---|---|
| Oxidative curing | Oxidative curing plus additional cross-linking |
| No hardener added | Hardener in the specified ratio |
| No pot life limit due to hardener | Limited pot life after mixing |
| Sufficient for many applications | Benefits when greater durability and faster curing are required |
More isn’t automatically better. Not every wood surface needs a hardener. The key factors are how it will be used and choosing the right oil system.
When is OLI NATURA® Hardener the right choice?
Ready to use sooner. More durable in everyday use. Better protected against moisture.
That’s exactly where the 2K application comes into its own.
It is especially recommended when faster curing and therefore earlier use, greater durability or improved water repellency are desired.
This is particularly beneficial for heavily used floors, stairs, tabletops and work surfaces, as well as bathroom furniture and vanity tops - provided the oil system used is approved for this application.
More protection against moisture: Additional chemical cross-linking makes the cured oil system more resistant to water. It repels moisture more effectively, so less water penetrates the wood.
With traditional impregnating oil systems, the surface remains breathable. It is not completely sealed. For this reason, standing water should still be avoided.
Does a hardener help with a fine final sanding?
The sanding makes all the difference. That’s because the final grit affects how well wood absorbs oil and color pigments.
Sanding too finely can reduce oil absorption. For approved oil systems, the appropriate hardener can support additional cross-linking and curing of the absorbed oil.
However: A hardener does not replace adequate oil absorption. The recommended final grit is still determined by the specifications for each product.
Which wood oils can be used with OLI NATURA® Hardener?
Not every wood oil is suitable for adding hardener. OLI NATURA® Hardener may only be combined with approved oil systems.
The following mixing ratios by volume apply to the products listed below:
| OLI NATURA wood oil | Oil : hardener |
|---|---|
| HS Professional Oil, clear | 10 : 1 |
| Colour HS Professional Oil | 10 : 1 |
| Worktop-Oil | 5 : 1 |
| Colour-Oil Midnight-Black | 5 : 1 |
In simple terms:
For a 10:1 ratio, mix 1,000 ml of oil with 100 ml of hardener.
For a 5:1 ratio, mix 500 ml of oil with 100 ml of hardener.
Important: Only combine approved products. The current technical data sheets are binding.
For water-based OLI NATURA® Scandic-Oil systems, use the separately designated OLI NATURA® H2O-Hardener.
How should OLI NATURA® Hardener be used correctly?
1. Prepare properly
Sand the wood evenly to the recommended final grit. The surface must be clean, dry, and dust-free.
2. Mix correctly
Thoroughly mix the oil and hardener in the specified ratio immediately before use. Only prepare as much as can be used within the pot life.
3. Observe the pot life
After mixing, the mixture can only be processed for a limited time. This is known as pot life. Once it has elapsed, the mixture must not be used.
4. Work in the oil
Apply the mixture evenly in accordance with the technical data sheet. With suitable high-solid oils, a beige pad helps work the oil into the wood surface.
5. Remove excess
Anything the wood does not absorb must be removed.
After the specified penetration time, remove excess oil with a suitable oil-absorbing cloth. For classic, non-film-forming oils, then polish the surface with a white pad until no residue remains.
The rule of thumb: After buffing, the surface should feel dry to the touch.
6. Allow to cure
Dry ≠ fully cured. Chemical cross-linking continues even when the surface already appears dry.
Protect from water and heavy use until fully cured. Ensure adequate air circulation and observe the product-specific curing times.
What is important for occupational safety?
OLI NATURA® Hardener is a reactive hardener additive based on isocyanate.
Solvent-free does not mean free of hazardous substances.
Avoid skin contact, wear suitable protective gloves, and ensure adequate ventilation.
Also important: Oil-soaked cloths and pads can spontaneously ignite due to heat buildup. After use, store them safely or dispose of them immediately according to the manufacturer's instructions.
In summary: Not always necessary, but a targeted advantage.
The OLI NATURA® Hardener enables additional chemical cross-linking and can thereby accelerate curing, increase durability, and improve water repellency.
With approved colored oils, pigment binding can also benefit.
Not every wood oil needs a hardener. But when requirements increase, additional cross-linking can make all the difference.
The right oil system, correct dosage, and professional application are always essential.
The VOC-free OLI-NATURA HS Hardener accelerates curing, improves resistance, and is added to the oil at the specified mixing ratio.
Shake OLI-NATURA HS Hardener well shortly before use, mix thoroughly with the oil in the specified ratio, and apply at room temperature.
Apply the oil-hardener mixture as directed. Use immediately and do not pour excess material back into the container. Pot life is 2-3 hours, depending on the type of oil.
Expert article by OLI NATURA®
Written by Sylke Schubert-Temmen
Last updated on 04.11.2026
