Thermally Modified Spruce vs Untreated Spruce for Sauna Applications

Spruce is a popular softwood for interior construction because it is lightweight, easy to process and naturally attractive.

However, when spruce is used in a sauna, buyers should consider more than price and appearance.

The main question is:

Should you choose untreated spruce or thermally modified spruce for your sauna project?

The answer depends on the project design, expected environmental conditions, budget and required wood performance.

Untreated Spruce

Untreated spruce maintains the natural properties of fresh or kiln-dried spruce.

Its advantages include:

• Natural light color
• Familiar wood appearance
• Good workability
• Lightweight structure
• Easy machining
• Competitive material cost

For suitable indoor environments, untreated spruce can be a practical material.

However, untreated wood remains sensitive to environmental moisture changes.

Thermally Modified Spruce

Thermally modified spruce undergoes controlled heat treatment.

The process modifies the wood's relationship with moisture and changes its natural color.

Typical advantages include:

• Improved dimensional stability
• Reduced moisture absorption
• Deeper natural color
• Improved durability characteristics
• Natural wood appearance
• Good suitability for certain demanding environments

Moisture Behavior

This is one of the most important differences.

Untreated spruce naturally absorbs and releases moisture as environmental conditions change.

Thermal modification reduces the wood's hygroscopic behavior.

For sauna interiors, where temperature and humidity fluctuate repeatedly, this characteristic can be valuable.

Appearance

Untreated spruce is normally light in color.

Thermally modified spruce becomes darker because of the heat-treatment process.

Therefore:

Untreated spruce = light and natural

Thermally modified spruce = warm brown and natural

The choice depends on the design language of the sauna.

Dimensional Stability

Wood movement is a normal characteristic of timber.

Thermal modification can reduce moisture-related dimensional changes.

For sauna walls and ceilings, improved stability can help maintain a more consistent appearance over repeated environmental cycles.

Which One Should You Choose?

Choose untreated spruce when:

• Budget is a major consideration
• A light wood appearance is preferred
• The application has relatively moderate environmental conditions
• The project specification calls for conventional spruce

Consider thermally modified spruce when:

• Improved dimensional stability is important
• A darker wood appearance is preferred
• The project experiences repeated moisture changes
• The customer wants thermally modified timber
• Natural durability characteristics are valued

What About Sauna Benches?

Sauna benches are a specialized application.

The surface temperature and direct user contact requirements can be different from wall and ceiling applications.

Therefore, the wood species, grade, profile and finish should be selected specifically for the intended sauna component rather than assuming that one wood specification is suitable for every part of the room.

LinkedIn Woodwork Supply

LinkedIn Woodwork manufactures and processes solid wood products and thermally treated timber in Shandong, China.

The company website currently lists thermal-treated wood, pine/spruce wood, solid wood processing, drying, inspection and R&D among its product and production capabilities.

We can discuss customized specifications for sauna manufacturers, importers and distributors.

Contact us to compare untreated spruce and thermally modified spruce for your next sauna project.