Sauna stones: good steam, and knowing when to replace them

Most heaters arrive with rounded stones, and they work. We use irregular ones in our own saunas because we prefer the steam off them. It is a preference, not a rule, but if you are replacing a set anyway, it's worth trying irregular.

• Wait until the stones are hot. Pour a little and watch. If the water is still trickling down through the stones, they aren't ready. You want it to vanish the moment it lands.
• Start with half a ladle. The temperature on the thermometer won't change, but it will feel a lot hotter. Half a ladle gives everyone a chance to see how it feels, and to move down a bench if they want to.
• Ask first. In a shared sauna, check with everyone before any water goes on.
• Pour back to front, and spread it. Pouring from the back of the stones towards you saves steaming your own arm, and spreading the water across all the stones gives a nicer hit of steam than one spot.
• Don't douse. Pouring water onto stones that are still wet cools them off. Give them time between ladles.
• Warm the bucket. Warm water turns to steam more easily. Stand the bucket on the lower bench: the floor isn't warm enough and the top bench makes the handle too hot to hold.

Our Steam & Löyly video shows all of it, including what stones look like when they aren't ready yet.

Fresh water, always. Never sea water and never anything wrung out of a wetsuit. Everything that goes on the stones gets breathed in.

Essential oils go in the bucket, never straight on the stones, where they can catch fire. Go easy in a mixed group: a scent one person loves can spoil the session for someone else. We use eucalyptus as standard because nearly everyone likes it. With a small bottle, five or six drops in the bucket is enough to smell without it being overpowering. There's more on scents in our guide to sauna aromatherapy.

Once a month, take the stones off and hoover out under the heater's little hatch. It does wonders for the air flow and the draw, and it gives you a regular look at every stone.

The test is simple: knock two stones together. If they crumble or sound hollow, or they've split, they're done. It is nearly always the top stones, or the ones right around the stove, that go first.

When it's time, replace all of them in one go, not just the top layer: it's good practice to do them all in one sitting. As a rough guide that comes round about once a year, and sooner in a commercial sauna working most days, but let the knock test decide rather than the calendar.

Empty the bucket at the end of every day, even off grid where it's tempting to keep the water. A wooden ladle left standing in water splits, and quickly. Metal ones rust, and the little pins that hold the handle on go first. Fresh water each day, and an empty bucket overnight.

Everything else that keeps a sauna in good order, from the benches to the chimney, is in our builds FAQ and the maintenance video.