Silicone Sealant: Where and When to Use It in Your Sauna

Silicone Sealant: Where and When to Use It in Your Sauna

Silicone sealant is a flexible, waterproof adhesive used to seal gaps and joints. In sauna construction, it shows up in a few specific places where you need a heat-resistant, moisture-proof seal. But using the wrong type or putting it in the wrong spots can cause problems, so it pays to know the basics before you start squeezing tubes.

Types of Silicone Sealant for Sauna Use

Not all silicone is the same. Here is what you need to know about the different types and where each one belongs:

• High-temperature silicone (red or black): Rated for 400-600F continuous exposure. This is what you use near heaters, chimney penetrations, and anywhere that gets seriously hot. The red and black formulations sold for automotive gasket work are widely available at any auto parts store. Look for brands like Permatex or RTV silicone rated to at least 500F.
• Standard exterior-grade silicone: Rated for about 300-400F and designed for outdoor weather exposure. Use this for exterior sealing on outdoor saunas: roof joints, wall penetrations, and anywhere rain might get in. These surfaces do not reach extreme temperatures, so standard exterior silicone holds up fine.
• Kitchen and bath silicone: The white or clear stuff from the hardware store with mold inhibitors built in. This is NOT suitable for the hot zones of a sauna. The mold inhibitors can off-gas at high temperatures, producing unpleasant fumes in an enclosed space. Keep this one in the bathroom where it belongs.
• Food-grade silicone: Some sauna builders prefer food-grade silicone for any sealing near the interior hot zone because it is certified not to release harmful chemicals when heated. More expensive but gives peace of mind if you are sealing near areas that get above 300F.

Heat Resistance Ratings Explained

Silicone sealants are rated for both continuous and intermittent heat exposure. The continuous rating is the temperature the sealant can handle indefinitely without degrading. For sauna use:

• Near the heater or chimney: You need continuous ratings of 500F or higher. Chimney pipe surfaces can reach 600F+ during a firing cycle.
• Interior walls and ceiling (not near heater): The air temperature tops out around 200F, but surfaces near the ceiling can hit 250F. A sealant rated for 400F continuous is adequate here.
• Exterior surfaces: Temperature rarely exceeds 150F on the exterior, even in direct sun. Standard exterior silicone is more than sufficient.

Where to Use Silicone in Saunas

• Chimney penetration: If you have a wood-burning sauna, the chimney pipe passes through the roof. The flashing around that penetration needs high-temperature silicone sealant.
• Electrical entry points: Where wiring enters the sauna through the wall, silicone keeps moisture out.
• Glass door edges: Some glass door installations use silicone to seal the glass panel in its frame.
• Drain fittings: Around floor drains and barrel drain plugs to prevent leaks.
• Roof seams on outdoor saunas: Some manufacturers recommend sealing roof panel joints on outdoor saunas to prevent rain infiltration.
• Vapor barrier seams: Where sheets of foil vapor barrier overlap, high-temp silicone or foil tape seals the joint.

Application Tips for a Clean, Lasting Seal

Getting a good silicone seal takes a bit of technique:

• Surface prep: Clean the surfaces with isopropyl alcohol before applying. Silicone will not bond well to dusty, oily, or damp surfaces.
• Cut the tip at 45 degrees: A diagonal cut gives you better control over the bead size and lets you push the silicone into the joint as you go.
• Apply in one continuous bead: Start at one end and pull the caulk gun steadily to the other end. Stopping and starting creates weak spots.
• Smooth with a wet finger or tool: Within 2-3 minutes of application, smooth the bead with a wet finger, a caulk finishing tool, or a popsicle stick dipped in soapy water. This presses the silicone into the joint and gives a clean finish.
• Cure time: Most silicone sealants need 24 hours to fully cure. Do not fire up the sauna during this time. High-temp silicone can take up to 48 hours.
• Tape for clean lines: Apply painter's tape on both sides of the joint before laying the bead. Remove the tape immediately after smoothing, before the silicone starts to skin over.

Where NOT to Use It

• Between wall panels: Tongue-and-groove joints are designed to expand and contract with temperature changes. Sealing them with silicone fights that natural movement.
• Bench surfaces: Silicone on surfaces that get sat on will smear and look terrible.
• Anywhere the manufacturer says not to: Follow the installation manual. If it doesn't mention silicone, you probably don't need it there.

Related Terms

• Sauna Assembly Tools
• Weatherstripping for Sauna Doors
• Barrel Plug Drain
• Sauna Roof Options

Build with Confidence

Browse our outdoor saunas and indoor saunas - installation manuals included with every kit tell you exactly where sealant is needed.