Oiling Thermowood: Is It Actually Necessary?

Many customers assume thermowood will deteriorate like natural wood if it isn't oiled. In reality, thermowood is engineered from the start to resist moisture and rot, so oiling is a choice, not a structural necessity.

What is thermowood, and why is its color so dark?

During a controlled high-temperature heating process, the wood's cellular structure changes: the natural sugars that feed fungi and insects break down, which is what gives thermowood its dark brown color and its inherent resistance to moisture and decay. For a full comparison with ordinary natural wood and where each one fits, read Thermowood vs. Natural Wood.

Oiling is optional, not mandatory

Left untreated, outdoor thermowood gradually fades to a silvery grey — the same thing that happens to any wood under the sun. This greying is purely cosmetic and doesn't affect the wood's resistance to moisture or rot. Oil simply preserves the original brown color and adds extra protection against UV rays.

• Exterior facades and terrace decking: if keeping the original warm color matters, oiling is recommended
• Interior sauna or steam room walls: no oil needed — no sun exposure and no one cares about the color there
• High-traffic terrace flooring: an anti-wear oil extends the floor's visual lifespan

Thermowood turning grey isn't a sign of damage — it's a sign the wood is doing its job under the sun.

How often to oil, and the right way to do it

The surface must be completely clean and dry before oiling, using an oil made specifically for exterior wood with UV protection — not any ordinary indoor wood oil. Surfaces exposed directly to strong summer sun usually need a fresh coat every year; shadier or less sun-exposed surfaces can go up to two years between coats. If you've left it too long and the color has gone fully grey, a light wash or gentle sanding is needed before oiling.

Floors need different care than walls and facades

Terrace flooring takes direct foot traffic and contact, so it needs an anti-wear oil — details are in Thermowood for Terrace Flooring. Interior walls and decorative panels usually just need the standard UV oil, and far less often, since they're not exposed to direct rain or foot traffic.