Maintaining the wood of your outdoor sauna

Short answer: outdoors, thermowood needs little attention (clean annually, oil only if you want to keep the brown colour) and spruce needs a fixed annual treatment with stain or oil. Indoors, one strict rule applies: never lacquer or paint, only a lightly damp cloth and optionally sauna wax. Below is the complete calendar per wood type and the care of the interior.

Which wood is used where on your sauna

At Qrest, the exterior of the Q-cube and Q-linder is finished in thermowood; on the Quatro it is thermowood or spruce. Thermowood is softwood treated with steam at around 200 °C, without chemicals: as a result it absorbs almost no moisture, barely warps or cracks, and is resistant to rot. Spruce is light and natural in appearance, but absorbs moisture when untreated and therefore requires consistent maintenance. Inside, the finish consists of alder, supplemented with thermowood: alder contains almost no resin, does not splinter and stays pleasant against the skin at 70 to 90 °C.

Exterior maintenance calendar

Method for treatment: use a product suited to the wood type (special oils exist for thermally modified wood), work on clean, dry wood, and never treat in full sun. Greying itself is purely cosmetic: untreated thermowood slowly turns silver-grey under UV light without losing strength. If you want the caramel colour back: sand lightly, remove the dust, let it dry and only then oil it; the colour sits deep in the wood and returns almost completely.

Caring for the interior

1. After every session: let the sauna dry out with the door ajar until the wood feels dry, and wipe off any visible sweat marks on the benches.
2. Periodically: wipe benches and walls with a lightly damp cloth and, if needed, a mild soap solution; rinse thoroughly and let dry.
3. Protection: if desired, treat the benches with special sauna wax or paraffin oil for indoor use. This makes the wood more resistant to sweat and moisture.
4. Never: lacquer, paint or regular wood oil inside the cabin. The wood needs to be able to absorb and release moisture; a sealed coating blocks that, gets hot and can give off fumes.
5. Always sit with a towel: the simplest protection for the benches; see also sauna temperature and loyly.

The full cabin care routine (ventilation, stones, seasonal checks) is in outdoor sauna use and maintenance.

Common mistakes

• "Forgetting" spruce in the first few years: new spruce needs the protective coats the most; a maintenance backlog is difficult to catch up on later.
• Lacquering or painting inside: the most common and most stubborn mistake; removing it means sanding it back completely.
• Treating wet wood or working in the sun: the oil or stain adheres poorly and leaves marks.
• Aggressive cleaning with a pressure washer: a pressure washer damages the wood fibre; water and a soft brush are sufficient.