Untreated wood in a sauna is not merely an aesthetic issue. As we like to say: untreated sauna wood means an unfinished sauna.
Why?
The pores of untreated wood are not protected or sealed. They act like a sponge, absorbing moisture, perspiration and dirt. As a result, dark stains, residue and unpleasant odours may develop on the benches and walls. Over time, these can become very difficult — or even impossible — to remove completely.
This is especially relevant in saunas where birch whisks, herbs, scrubs, clay, honey or other body-care products are used.
Is it safe to treat sauna wood?
Some people choose to leave the wood untreated because they are concerned that protective products may release unwanted substances when heated. These concerns are understandable, which is why ordinary furniture oil, varnish or outdoor wood treatment products should never be used inside a sauna. Our selection includes only tested, specialised sauna wood treatment products from the Finnish manufacturer Tikkurila.
Waxes and oils designed for sauna use are developed specifically for high temperatures and humid conditions. For example, Tikkurila Supi Saunavaha is a water-based product containing natural wax. It penetrates the wood and helps protect it against water and dirt. Some professional sauna waxes also carry the M1 low-emission classification.
Natural linseed oil is not the only, nor automatically the best, solution. It can have a strong smell, require a long drying time and significantly alter the colour of the wood. The most important question is therefore not simply whether a product is “natural”, but whether it is suitable for the specific sauna surface and intended for use in high temperatures.
What do sauna wood protection products do?
Protective products designed for saunas penetrate the wood and create a protective layer that reduces the absorption of moisture and dirt.
A treated wooden surface:
- retains its fresh and well-maintained appearance for longer;
- is easier to clean;
- absorbs less moisture, perspiration and dirt;
- is better suited to intensive sauna use;
- lasts longer.
Treatment does not make the wood completely resistant to dirt, but it makes everyday maintenance significantly easier and helps prevent permanent staining.
Oil or wax?
Both oil and wax help protect sauna wood, but their properties differ slightly.
Supi Laudesuoja oil penetrates the wood and helps repel moisture and dirt. It preserves a natural surface feel, although the protective layer usually needs to be renewed more frequently. Oil is often chosen for sauna benches and other surfaces that regularly come into contact with the body and water.
Supi Saunavaha wax also penetrates the wood, while creating a more noticeable protective layer. The surface becomes smoother, silkier and easier to maintain. Wax protection generally lasts longer and can be used on benches, walls and ceilings.
Does a protective product change the colour of the wood?
Yes, protective products may slightly alter the appearance of the wood. In most cases, the colour becomes richer and the natural grain more pronounced. In the samples below, the wood has been treated with one coat: aspen with transparent wax and thermowood with oil.
The final colour change depends on the wood species, the chosen treatment product and the number of coats applied. We therefore recommend testing the product on a small, less visible area before treating the entire surface.
Immediately after treatment, the colour may appear stronger and more saturated. The final result should only be assessed once the surface has dried completely. After several sauna sessions, the tone usually becomes softer and more natural.
Typical colour changes in different wood species:
- Aspen becomes slightly more yellow;
- black alder develops a more noticeable pinkish tone;
- thermowood becomes darker and its grain appears more pronounced.
Which sauna surfaces should be treated?
The greatest attention should be given to sauna benches, backrests and other surfaces that come into contact with the body.
Depending on the chosen product, it may also be suitable for:
- walls and ceilings;
- wooden floors;
- steps;
- armrests;
- other wooden details inside the sauna.
In a new sauna, apply the protective product to a clean, dry and untreated surface. Use a brush, sponge or cloth, depending on the product instructions.
If the benches have already been used, they should first be cleaned thoroughly:
- Warm the sauna slightly so that the wood becomes more receptive to cleaning.
- Wash the surfaces with a Tikkurila cleaning product designed for sauna use.
- Rinse with clean water.
- Allow the wood to dry completely.
- Apply the oil or wax evenly, following the manufacturer’s instructions.
If the benches are heavily soiled and the stains can no longer be removed completely, lightly sand the surface to remove the damaged top layer. Then repeat steps 2–5.
How should a sauna be maintained day to day?
Even treated wooden surfaces require regular care to keep the sauna benches looking clean and well maintained for longer.
After each sauna session, we recommend:
- rinsing away any visible dirt;
- allowing the sauna to dry properly using the residual heat;
- opening the ceiling ventilation;
- ventilating the surrounding rooms once the sauna itself has dried.
A common mistake is to open the sauna door wide immediately after use. This allows heat and moisture to escape into the adjacent rooms, while the sauna loses the residual heat that would otherwise help dry the wooden surfaces.
Once the sauna has dried, clean the benches with ONNI sauna cleaning spray. The surfactants in the product help lift perspiration, grease and everyday dirt from the benches, while the alcohol supports effective cleaning and faster drying. After cleaning, always rinse the benches with clean water and allow them to dry completely.
Our collection also includes other ONNI everyday cleaning products designed for quick and effective maintenance of wooden surfaces, glass, bathrooms and WC areas. The products feature fresh Nordic-inspired scents such as eucalyptus, pine, verbena and cedar. They help keep the space clean while leaving behind a pleasant, fresh fragrance.
ONNI products are intended for regular everyday maintenance, helping prevent dirt from penetrating the surfaces. Once or twice a year, we also recommend carrying out a more thorough sauna clean using Tikkurila Supi Saunapesu.
Keep your sauna looking beautiful for longer
Treating sauna wood is not simply a matter of appearance. It is a practical part of completing the sauna, helping wooden surfaces remain clean, well maintained and easier to care for.
Protecting new wood from the start is far easier than trying to remove deeply absorbed perspiration, water marks or stains from sauna rituals later on.
Our recommendation is simple: before you begin using your new sauna regularly, treat the wooden surfaces with a protective product designed specifically for sauna use. It is a small task at the beginning that will make maintenance much easier and help your sauna retain its beautiful appearance for years to come.