What does a hardener do in wood oil? When is 2K application worthwhile, and what should you bear 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.
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, making the surface 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 penetrated 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 further chemical cross-linking reactions.
To put it simply: You can think of cross-linking like a woven fabric. The more closely the threads are connected, the stronger the fabric becomes.
Similarly, additional chemical cross-linking can make the cured oil system more resistant.
Four benefits at a glance:
- Ready to use sooner: Curing is accelerated. The surface reaches its load-bearing capacity sooner.
- Greater durability: The cured oil system becomes more resistant to everyday wear.
- Improved water repellency: Additional cross-linking can significantly improve water resistance.
- Stronger pigment bonding: With suitable colored oils, resistance to color abrasion can increase.
Key point: The hardener does not replace oxidative drying. It complements it with additional chemical cross-linking.
1K or 2K - what is 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 prescribed ratio |
| No pot life limited by hardener | Limited pot life after mixing |
| Sufficient for many applications | Benefits when higher durability and curing performance are required |
More is not automatically better. Not every wood surface needs a hardener. The key factors are the intended use and the right oil system.
When is OLI NATURA® Hardener worthwhile?
Ready to use sooner. More resistant to everyday wear. Better protected against moisture.
That is exactly where 2K application comes into its own.
It is especially recommended when faster curing and therefore earlier usability, 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.
Better moisture protection: Additional chemical cross-linking makes the cured oil system more resistant to water. It repels moisture more effectively, making it less likely to penetrate the wood.
With classic impregnating oil systems, the surface remains open to diffusion. It is not completely sealed. Prolonged exposure to standing moisture should therefore still be avoided.
Does a hardener help with a fine final sanding?
Sanding makes the difference. The final grit affects how well the wood absorbs oil and color pigments.
Sanding too finely can reduce oil absorption. For oil systems approved for this purpose, the appropriate hardener can help further cross-link and cure the absorbed oil.
However: 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 volume-based mixing ratios apply to the products listed below:
| OLI-NATURA wood oil | Oil : hardener |
|---|---|
| HS Professional Oil, colorless | 10 : 1 |
| Colour HS Professional Oil | 10 : 1 |
| Worktop-Oil | 5 : 1 |
| Colour-Oil Midnight-Black | 5 : 1 |
Simple calculation:
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: Combine only 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 applied correctly?
1. Prepare thoroughly
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 application. Prepare only 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 period is called pot life. Once it has elapsed, the mixture must not be used.
4. Work in the oil
Apply the mixture evenly according to the technical data sheet. With suitable high-solid oils, a beige pad helps work it into the wood surface.
5. Remove excess
Whatever the wood does not absorb must be removed.
After the specified dwell time, remove excess oil with a suitable oil-absorbent cloth. For traditional, non-film-forming oils, then buff 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 follow the product-specific curing times.
What is important for workplace safety?
OLI NATURA® Hardener is a reactive hardener additive based on isocyanate.
Solvent-free does not mean hazard-free.
Avoid skin contact, wear suitable protective gloves, and ensure adequate ventilation.
Also important: Oil-soaked cloths and pads can spontaneously combust due to heat buildup. After use, store or dispose of them safely immediately, following the manufacturer's instructions.
Conclusion: 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.
Pigment bonding can also benefit with approved colored oils.
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 important.
Expert article by OLI NATURA®
Written by Sylke Schubert-Temmen
Last updated on
