Treating the wood and what to avoid
The wood does not need chemical treatment. Optional sauna-safe oil for exterior cosmetic upkeep. Never apply varnish, polyurethane, sealant, or any film-forming finish.
The wood in your sauna does not need any chemical treatment for normal use. Nordic Spruce is thermally modified, which provides built-in rot resistance. Canadian Red Cedar is naturally rot-resistant from its thujaplicin oils.
What you can do (optional)
- For exterior wood that you want to maintain in its original color, periodic application of a sauna-safe wood oil (specifically labeled for sauna use) can preserve the look. This is purely cosmetic. Untreated wood weathers to a soft silver-grey, which many owners prefer aesthetically.
- For interior wood, do not apply any treatment. The interior wood needs to breathe and absorb moisture.
What never to do
- Do not apply varnish, polyurethane, sealant, or any film-forming finish to any wood surface inside or outside the sauna. These products release fumes when heated and can fail under thermal cycling.
- Do not use deck stain or general-purpose wood treatments. These are not formulated for sauna use.
- Do not pressure-treat or chemically treat any replacement wood components.