Each Sauna comes pre-finished with one coat of Sikkens proluxe cetol srd stain (natural). According to manufacturer, it should not be recoated until water will not bead off the surface. The side of the sauna that sees most sun will need to be recoated more often than the shady side of the sauna. Do not let the finish go too long before recoating. Here is the link to manufacturer recoating process
When adding water to the rocks to create steam, avoid using softened water as it contains salt and will decrease the life of the stove and chimney pipes.
The interior can be cleaned with a combination of warm water and vinegar, dish soap, or chemical free detergent. Scrub on and hose off, then leave the door open to let it air out