How To Treat And Protect Sauna Wood

Paraffin oil has been used for decades in sauna rooms and is one of the most popular and effective ways to protect your sauna wood How To Treat & Protect Sauna Wood For Longevity – but here’s the thing most people don’t realize: treating the interior and exterior of your sauna requires completely different approaches. Get it wrong, and you could be breathing in harmful chemicals every session.

Here in Minnesota, where winter temperatures hit -20°F and summer humidity can feel like a steam room already, we’ve learned exactly what works (and what definitely doesn’t) for protecting sauna wood. This guide breaks down the right way to treat both interior and exterior sauna wood, what products to use, and which mistakes could ruin your investment – or worse, your health.

You’ll walk away knowing exactly when to use paraffin oil versus exterior stain, how often to treat different surfaces, and why that bottle of deck stain should never go anywhere near your sauna’s interior.

What You Need to Know About Sauna Wood Treatment

Let’s get straight to it – sauna wood treatment isn’t like finishing your deck or staining your fence. The combination of extreme heat (180-200°F), high humidity, and direct skin contact creates unique requirements that standard wood products can’t handle.

The golden rule? Interior and exterior surfaces need completely different approaches. Under no circumstances should wood inside the sauna be painted, varnished, impregnated or treated with wood preservatives. Wood care in the sauna – these products release toxic vapors when heated. But your exterior? That’s a different story entirely.

Sauna wood – whether it’s cedar, hemlock, or Nordic spruce – is specifically selected for its natural resistance to heat and moisture. Cedar contains natural oils that repel water. Hemlock stays dimensionally stable through temperature swings. These woods are already working hard for you before any treatment.

The truth is, many sauna owners never treat their interior wood at all, and their saunas last for decades. We’ve seen 20-year-old cedar saunas that have never seen a drop of oil still looking great.

Think of it this way: treatment is insurance, not a requirement. It’s about maintaining that new-sauna look and feel for longer, not preventing catastrophic failure.

Interior Wood Treatment: The Safe Approach

For interior surfaces – your benches, walls, backrests, and ceiling – safety trumps everything else. Emulsified oils are ideal for treating saunas because some contain very few solvents or none at all, and produce little or no VOC How to protect the interior wood of a sauna? – Ardec – Finishing Products. You’re sitting on these surfaces at 180°F, breathing deeply. Whatever you put on that wood becomes part of your sauna experience.

What Actually Works (and Won’t Poison You)

Paraffin Oil – This is our go-to recommendation. It’s food-grade, hypoallergenic, and creates zero harmful vapors when heated. Paraffin oil will work on all wood types used in sauna rooms. One liter covers about 150 square feet of bench surface. The wood darkens slightly – think of how cedar looks when wet – but that’s it.

Food-Grade Mineral Oil – Similar to paraffin but slightly thinner. Works great for spot treatment or if you can’t find paraffin oil locally.

Sauna-Specific Waxes – Products like Tikkurila Supi Saunawax are water-based and designed specifically for high-heat environments. They’re pricier than paraffin oil but offer excellent protection.

What to Never Use Inside

When exposed to the high temperatures typical of a sauna, paints can release volatile organic compounds (VOCs) and other harmful chemicals into the air Why Saunas AVOID Using Harsh Black Paint as a Stain. Here’s what stays outside:

• Any paint or primer (yes, even “low-VOC” versions)
• Polyurethane or varnish
• Deck stains or sealers
• Standard wood oils with drying agents
• Anything containing solvents

The “Do Nothing” Option

Here’s something we mention all of the time: leaving interior wood completely untreated is perfectly fine. Many Finnish saunas never see any treatment (including our own). The wood develops a natural patina over time, and as long as you’re ventilating properly after each use, it’ll last for years.

If you go this route, just wipe benches with a damp cloth occasionally and ensure good airflow after sessions. Simple as that.

Exterior Wood Protection: Weather-Proofing Your Investment

Now the exterior – that’s where you can (and should) get more aggressive with protection. Minnesota weather is brutal on exposed wood. We’re talking temperature swings of 120°F throughout the year, driving rain, snow load, and UV exposure that’ll turn beautiful cedar gray in a single summer.

Your Exterior Treatment Options

Semi-Transparent Stains – A semi-transparent stain will still allow the wood grains and natural color of the wood to show through. Brands like Sikkens and Cabot make excellent products that last 3-5 years between applications. We recommend staying away from solid stains – they hide the wood grain and look more like paint—unless you’re going for that look.

Water-Based Stain and Seal Combos – A water-based stain and seal protects against moisture and sun damage while allowing the wood to breathe Outdoor Sauna Maintenance. These typically need reapplication every 2-3 years but are easier to work with than oil-based products.

UV-Inhibitor Clear Sealers – If you love the natural wood color, these products protect against sun damage without adding tint. Just know you’ll be reapplying annually in sunny locations.

The Natural Weathering Approach – Cedar and other sauna woods will naturally weather to a silver-gray patina. Some folks love this look – it’s maintenance-free and has that authentic, aged appearance. Expect the exterior of your sauna to deteriate sooner than it would if it were finished. Some saunas (like our Northstar and Euro Series) require the exterior of the sauna to be sealed for the warranty to remain intact—always check your sauna warranty.

Application Tips That Actually Matter

Timing is everything with exterior treatment. Apply stain when the wood moisture content is below 15% – usually means waiting for a stretch of dry weather. In Minnesota, that sweet spot is typically late May or early September.

Use a pump sprayer for the main surfaces (if you have one—otherwise a brush will work), then back-brush to work it in. Don’t forget the end grain on your staves – that’s where water loves to sneak in. For barrel saunas, We recommend using a staining brush to stain the exterior of the front and back panels, as well as the edges of the staves and at the stave joints.

One gallon typically covers a 6×8 outdoor sauna with two coats. Buy the good stuff – spending an extra $20 on quality stain saves you from recoating in two years instead of five.

Common Treatment Mistakes That’ll Cost You

We see these mistakes constantly, and they’re expensive to fix:

Mistake #1: Using Interior Products Outside (or Vice Versa) Ensure that the product you are using is designed for the right location.

Mistake #2: Treating Wet Wood Wood needs to be bone dry before treatment – we’re talking less than 20% moisture content, ideally closer to 15%. Treating wet wood is like putting lotion on before jumping in the pool.

Mistake #3: Over-Application More isn’t better. Thick coats of oil on interior benches stay tacky and actually attract dirt. Thin, even coats that soak in completely – that’s what you want.

Mistake #4: Mixing Treatment Types Do not use Supi Sauna Wax and paraffin oil on the same surfaces. Pick one product per surface and stick with it.

Mistake #5: Skipping the Test Spot It’s always best to apply a small amount to an unnoticeable area of your sauna prior to treating the entire room. Every wood batch is slightly different. That cedar from last year might react differently than this year’s lumber.

Step-by-Step Treatment Guide for Each Surface

Interior Bench Treatment with Paraffin Oil

1. Prep the Space Fire up your sauna to 150°F for 30 minutes, then shut it off and let it cool to about 100°F. This opens the wood pores and evaporates any moisture.
2. Warm the Oil Place your paraffin oil bottle near (not on) the heater while the sauna warms. Warm oil penetrates better – think 80-90°F, not hot.
3. Apply Thin and Even Use a lint-free cloth or sponge. Work with the grain, applying thin coats. The bottom side should be treated as well, since often the mould forms underneath the benches How to Treat Sauna Benches – woodcare.guide.
4. Let It Soak Wait 30-60 minutes. If the oil absorbs in less than 20 minutes, apply a second thin coat.
5. Wipe Excess Any oil sitting on the surface after an hour gets wiped off. You want penetration, not a surface film.
6. Cure Time Wait 24 hours before using the sauna. First session, run it empty at full temperature for 30 minutes to burn off any residual odor.

Exterior Stain Application

1. Check the Weather You need 48 hours of dry weather – 24 before and 24 after application. Temperature between 50-80°F is ideal.
2. Clean First Low-pressure wash (under 1,500 PSI) to remove dirt and mildew. Let dry completely – usually 2-3 days.
3. Apply in Sections Work on 3-4 boards at a time. Spray or brush on, then back-brush to work it in. Maintain a wet edge to avoid lap marks.
4. Don’t Forget Details Hit those end grains, joints, and anywhere water might pool. These spots need extra protection.
5. Second Coat Strategy If doing two coats (recommended for new wood), wait 4-6 hours between coats. Second coat goes on thinner than the first.

How Often Should You Treat Sauna Wood?

This depends on use, but here’s what works for most people:

Interior Surfaces:

• Heavy use (daily): Twice per year
• Regular use (3-4 times weekly): Once per year
• Light use (weekly or less): Every 18-24 months
• Never treated: That’s fine too – just clean occasionally

Exterior Surfaces:

• Full sun exposure: Every 2-3 years
• Partial shade: Every 3-5 years
• Full shade/covered: Every 5-7 years
• Natural weathering: Never (just accept the gray)

Signs it’s time to retreat? Interior wood looks dry or shows water stains that won’t wipe off. Exterior shows fading color, water soaking in instead of beading, or visible weathering at joints.

Your Questions Answered

Q: Can I use the same treatment product on cedar and hemlock? A: Paraffin oil will work on all wood types used in sauna rooms How To Treat & Protect Sauna Wood For Longevity. For exteriors, most stains work on both, though cedar typically needs less frequent reapplication due to its natural oils.

Q: Is it safe to treat benches while pregnant or with kids using the sauna? A: Paraffin oil is food-grade and completely safe once dried. We still recommend waiting 24 hours after application before use, and running the sauna empty first to burn off any residual odor. Never use chemical treatments on interior surfaces where people will be sitting.

Q: My interior wood is getting dark spots. Should I sand before treating? A: Light sanding with 220-grit paper works great for water stains or darkened areas. Sand with the grain, vacuum the dust, then apply your treatment. For deeper stains, use the next coarser grain size and always sand with the fiber Wood care in the sauna.

Q: How do I know if my exterior stain is still working? A: The water bead test – sprinkle water on the wood. If it beads up, you’re good. If it soaks in immediately, time to reapply. Also look for color fading or gray showing through at the joints.

The Bottom Line on Sauna Wood Treatment

Treating sauna wood isn’t complicated once you understand the basics: keep chemicals out of the interior, protect the exterior from weather, and remember that less is often more. One to two treatment times in a year is enough to keep the sauna wood in good condition.

Your next step depends on your situation:

• New sauna? Treat that exterior within the first year to lock in the color, but let the interior season naturally for a few months first
• Existing sauna showing wear? Start with a good cleaning, then apply appropriate treatments to problem areas
• Just want to maintain what you’ve got? Set a yearly reminder to inspect and decide if treatment is needed

Questions about which products work best for Minnesota weather? Give us a call at 612-505-9700 or stop by our Cokato showroom. We stock paraffin oil, sauna-safe cleaners, and can recommend the right exterior stain for your specific setup. Plus, you can see treated versus untreated wood samples to decide what look you prefer.

Remember – we grew up with saunas and use them daily. This isn’t just business for us; it’s about helping you get the most from your sauna investment.