Sauna Wood Care Guide: How to Protect and Maintain Your Sauna Wood

Sauna Wood Care Guide: How to Protect and Maintain Your Sauna Wood

The wood in your sauna takes a beating. Interior surfaces deal with extreme heat, humidity swings, and body sweat. Exterior surfaces face rain, UV, snow, and temperature changes. With proper care, quality sauna wood lasts 15-20+ years. Without it, you'll see problems - darkening, mold, cracking, and rough surfaces - within just a few years.

This guide covers both interior and exterior wood care, with specific advice for the FSC-certified heat-treated Canadian hemlock used in our saunas.

Understanding Your Sauna Wood

Why Heat-Treated Canadian Hemlock?

Heat-treated (thermally modified) hemlock is the gold standard for sauna construction. The heat treatment process bakes the wood at 400F+ in a controlled environment, which:

• Removes most of the moisture from the wood cells, reducing shrinkage and swelling by up to 50%
• Breaks down the sugars in the wood that mold and insects feed on
• Darkens the wood to a rich, warm brown color
• Improves dimensional stability so the wood moves less with humidity changes
• Increases natural resistance to rot and decay

This gives you a significant advantage from day one compared to untreated softwoods, but it doesn't make the wood maintenance-free. It still needs care.

Interior Wood Care

Routine Cleaning (After Every Session)

The most important thing you can do for interior wood is keep it dry between sessions.

1. Wipe down benches with a clean, dry towel after each use. Body oils, sweat, and mineral deposits soak into the wood and cause darkening over time.
2. Ventilate fully. Open the door and all vents for 1-2 hours after each session. The wood needs airflow to dry. Trapped moisture leads to mold and mildew.
3. Use a towel on the bench during sessions. Sitting directly on bare wood accelerates staining. A towel barrier catches most of the sweat before it soaks in.

Weekly Deep Clean

Once a week, scrub the benches and high-contact areas with warm water and a small amount of mild, unscented soap. Use a soft-bristle brush. Rinse with clean water and let the sauna air-dry completely.

Never use these on interior sauna wood:

• Bleach or chlorine-based cleaners
• Scented cleaners or essential oil soaps (the chemicals off-gas at sauna temperatures)
• Pressure washers (way too aggressive for interior surfaces)
• Standard furniture polish or wood cleaners (contain chemicals that aren't safe to breathe at high temperatures)

Sanding Interior Surfaces

Over time, interior benches develop rough patches, surface stains, and a worn look. Light sanding restores them.

• When: Every 6-12 months, or whenever the bench surface feels rough
• How: Sand with the grain using 120-150 grit sandpaper. For deeper stains, start with 80 grit then finish with 120.
• How much: You're removing a very thin layer - just enough to expose fresh wood. Don't aggressively sand the benches down.
• After sanding: Vacuum or wipe away all dust, then run the heater for 30 minutes to cook off any remaining fine particles.

Should You Treat Interior Wood?

This is a common question, and the answer is: generally no. Interior sauna wood should be left untreated (bare). Standard wood finishes, stains, oils, and sealants are not formulated for the extreme heat inside a sauna and can release harmful fumes.

The exception is paraffin-based sauna oil, which is specifically designed for interior sauna surfaces. Applied sparingly to benches, it creates a thin barrier that resists sweat absorption while being safe at sauna temperatures. It's optional - many sauna owners never use it and their saunas are fine.

Exterior Wood Care (Outdoor Saunas)

Exterior wood faces completely different challenges than interior wood. UV radiation, rain, snow, and temperature swings are the enemies here.

First Application (New Sauna)

If your outdoor sauna arrives untreated on the exterior (many do), apply an exterior wood treatment within the first few weeks of installation.

1. Make sure the wood is clean and completely dry.
2. Apply a high-quality exterior wood stain or oil designed for outdoor use. Look for products with UV inhibitors.
3. Apply with a brush, working the product into the grain. Two thin coats is better than one thick coat.
4. Let each coat dry for the manufacturer-recommended time (usually 24-48 hours).
5. Focus extra attention on end grain (exposed cut ends) - these absorb moisture fastest.

Annual Maintenance

Once a year (spring is ideal), inspect and refresh the exterior finish:

1. Clean the surface. Use a garden hose and a soft brush to remove dirt, pollen, and debris. Let it dry completely (24+ hours).
2. Inspect for damage. Look for cracking, peeling, or areas where the finish has worn away, especially on south-facing surfaces (highest UV exposure) and horizontal surfaces (most rain contact).
3. Lightly sand worn areas with 120 grit if the previous finish is peeling or flaking.
4. Reapply one coat of exterior wood stain or oil to all surfaces. Two coats on any bare wood you sanded.

Best Products for Exterior Sauna Wood

• Penetrating oil-based stains: These soak into the wood rather than forming a film on top. They don't peel or flake, which makes maintenance easier. Good options include Penofin, TWP, and Cabot Australian Timber Oil.
• Semi-transparent stains: These add color while letting the wood grain show through. They provide UV protection and moderate water resistance.
• Avoid film-forming finishes like polyurethane or lacquer on exterior sauna surfaces. These trap moisture and peel in the heat/humidity environment around a sauna.

Dealing With Common Wood Problems

Mold and Mildew

Mix 1 part white vinegar with 4 parts water. Apply to affected areas, let sit 10-15 minutes, scrub with a soft brush, and rinse clean. For persistent mold, sand the area after cleaning to remove any staining that penetrated the wood surface. Then fix the ventilation issue that caused the mold.

Dark Sweat Stains on Benches

Light sanding (120 grit) removes most surface stains. For deep stains that sanding alone won't fix, try oxalic acid wood brightener applied per the product's instructions, followed by sanding.

Cracking or Checking

Small surface checks (cracks along the grain) are normal in wood exposed to heat and humidity cycles. They don't affect structural integrity. If a crack is wider than 1/8 inch or goes through a structural member, consult the manufacturer.

For exterior checking, fill visible cracks with a flexible exterior wood filler before applying your annual stain coat.

Graying Exterior Wood

Untreated exterior wood turns gray within 6-12 months due to UV exposure. This is purely cosmetic - it doesn't affect the wood's durability. If you prefer the warm brown color, apply exterior stain with UV inhibitors. If you like the weathered gray look, leave it alone.

Wood Care Schedule Summary

All of our outdoor saunas and barrel saunas are built with FSC-certified heat-treated Canadian hemlock, which gives you a significant head start on durability and moisture resistance. Pair that with the care routine in this guide and your sauna will look and perform great for decades.