Sauna Maintenance, Part 2: The Exterior

In Part 1 we handled the inside. Now the outside — and here your sauna takes one of two roads.

Some of our saunas are left as natural cedar, and over a year or two they weather into a silver-gray patina we love. About half — maybe more — go out stained dark or in a custom color, and those hold their tone with a little upkeep. Neither is "better" than the other, they're just different. Find yours below.

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Path 1: Natural Cedar — Let It Gray

Silver and beautiful — like we'll all get, if we're lucky.

If your sauna is bare cedar, the care instructions are almost funny: do nothing. No stain, no sealer, no yearly coat of anything. Left alone, cedar doesn't fall apart — it turns silver. And that silver is our favorite thing a Nightjar ever does.

Why does cedar turn gray?

The graying isn't dirt and it isn't rot. It's light.

Wood is held together by two things: cellulose, the pale structural fiber, and lignin, the natural polymer that binds those fibers and carries most of the wood's color and warmth. When sunlight hits bare wood, the UV slowly breaks down the lignin at the very surface. Rain then rinses those loosened, colored compounds away, and what's left is a thin layer of weathered cellulose — which reads to the eye as that familiar silvery gray.

That's the whole trick. Sun breaks down the surface color, rain washes it clean, the wood settles into silver. And the key part: it's only skin-deep. A paper-thin surface layer. The wood underneath is exactly as strong, as thick, and as sound as the day it was installed.

Why cedar can do this without rotting

Plenty of woods gray. Most of them rot while they do it. Cedar is different, and it comes down to what's already inside it. Northern White Cedar — our favorite wood we build with — grows its own preservatives — natural oils (the ones you smell when you open the door) that resist moisture, fungus, and insects. So while the surface weathers to silver up top, the board itself stays protected from the inside out. That's why cedar has been the wood of choice for shingles, canoes, and saunas for as long as people have built with it. It ages instead of failing.

How we build for a beautiful, even gray

Left to pure chance, weathering can go blotchy. The difference between a sauna that grays beautifully and one that grays unevenly is in how it's built — and we design for it:

• We leave it unsealed on purpose. No factory coating fighting the process.
• We build it to drain and dry. Water sheets off and runs down instead of pooling — even weathering comes from even wetting and drying.
• We keep it up off the ground so the base isn't wicking moisture, which is where dark, uneven patches usually start.
• We build only with Northern White Cedar — light in color, strong, and loaded with natural oils — so it has the character to weather gracefully and the protection to do it for decades.

What you'll see, month by month

• Weeks 1–8: the warm honey tone starts to soften, faster on the sun-facing sides. Expected.
• Months 2–12: the color mellows through tans and light grays. This is the in-between phase — uneven on purpose, because sun and rain aren't uniform yet.
• Year 1–2: it settles into a silvery patina and mostly holds there. Grayed cedar doesn't march on to black — it just stays silver.

Caring for grayed cedar: basically nothing

Once it's silver, the exterior asks nothing of you. Keep it out of standing water, keep sprinklers from blasting one spot, and let the sky do the rest. If you ever miss the honey tone, a gentle wash or light sand brings it back — but we'd talk you out of it. The gray isn't the sauna wearing out. It's the sauna wearing in.

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Path 2: Stained or Colored — Keep the Finish Alive

If your sauna went out in a rich dark tone or a color, you made a beautiful choice — and you signed up for a little upkeep in exchange. A stain isn't just color; it's a protective finish sitting in and on the wood. Your job is simply to keep that finish healthy so it keeps looking the way it did on day one.

What the stain is doing

The stain penetrates the outer layer of the cedar and adds a shield against exactly the thing that grays bare wood: UV and water. That's why a stained sauna doesn't turn silver — the finish is absorbing the wear instead of the wood. But finishes are consumable. Sun and rain slowly spend them, and a little attention keeps you well ahead of it.

Keeping it clean

Same gentle approach as the inside: warm water, a mild, sauna-safe soap, and a natural fiber scrub brush. Wash off pollen, dust, and grime a couple of times a year so nothing sits on the finish and dulls it. Never use a pressure washer or anything abrasive — that strips stain faster than the weather does.

When to re-coat

Every few years the finish will start telling you it's thirsty. Watch for:

• Color fading or going flat, especially on the sun-facing and top surfaces.
• Water soaking in dark instead of beading up — the surest sign the shield is thinning.
• Dry, lighter patches where the finish has worn through first.

When you see those, it's time for a refresh coat — and the good news is you almost never have to strip anything. Clean the surface, let it dry fully, and apply a fresh coat of the same exterior stain we finished it with. Match the product and you keep the tone consistent and the protection intact. Catch it early and it's a quick job; let it go until the finish is peeling and bare wood shows, and it becomes real work. So don't wait for peeling — top it up while it's still just faded.

One rule that never changes

Whatever you use, it has to be an exterior, wood-appropriate, sauna-safe finish — the same class of product we built it with. Ask us and we'll point you to the exact match for your sauna. And this is all exterior only — the benches and interior always stay bare cedar, no matter what the outside is wearing.

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Silver or stained, the outside is easy

Two paths, same spirit. One lets nature do the work and turns silver like we'll all get. The other takes a wash and an occasional coat to hold its color. Neither should ever feel like a burden — that's the whole point of the way we build.

Let the bare ones gray. Keep the stained ones fed. Either way, sit in it more than you fuss over it.

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Missed the first half? Read Part 1: How to Clean a Sauna »

Got a cold plunge too? Read Part 3: Cold Plunge Maintenance »

Ready for one of your own? Explore our handcrafted cedar saunas »

— Nightjar Sauna, Grand Rapids, Michigan

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