What prevents a wet sauna from eventually getting mouldy?
—Edward Hanley, via e-mail
The proper ventilation. “Direct cross-ventilation is a must after each sauna,” says David Salmela, an architect and sauna designer in Duluth, Minn. Without ventilation—at minimum, enough to create a cross-draft in a stand-alone sauna building—you won’t be able to get rid of the humidity post-session. Plus, if it’s too airtight, the people inside won’t get enough oxygen. (The sauna is for relaxation, not nausea and blackouts.) If the sauna is indoors—in the basement, with no opportunity for exterior windows—you need an exhaust fan.
So, assuming your sauna was properly designed and you air it out after use, there’s no reason it should get mouldy. “I haven’t ever really seen mould in a sauna,” Salmela says. “The air is dry from the heat, so the steam dissipates.”
According to Eija Pyykkonen, who operates Finntastic Sauna in Thunder Bay with her husband, David, “it’s really no more moisture than would be generated during a long, hot shower.”
Proper sauna care will help too. It’s a good idea to clean the surfaces inside (if your benches are removable, dry them in
the sun periodically). Pyykkonen suggests using a mild wood cleaner such as Murphy Oil Soap diluted with water. And for the love of all that is hygienic—ask sauna users to sit on towels and wipe down the benches and backrests after every session. As Pyykkonen points out, “you don’t really want to sit in someone else’s sweat.”