Preserving the Pristine Beauty of Montana

Formed by glaciers during the last Ice Age, Flathead Lake is the largest natural freshwater lake west of the Mississippi—and one of the cleanest in the world, known for its stunningly clear water. With that purity comes strict building and usage regulations, including a ban on using chemically treated or enhanced materials for any construction on or near the water.

The crystal clear waters of Flathead Lake, Montana. Credit: Maja Holmquist

So, how do you build a dock on Flathead Lake without using chemicals?  Easy. You use thermally modified wood. Thermal modification has the unique benefit of making wood water and weather-proof without chemicals. Using only heat and steam, the thermal modification process changes the physical properties of wood, making it water, weather, and insect resistant and improving its durability and longevity.

This dock on Flathead Lake was built using thermally modified Doug Fir in the spring of 2019. Per regulations, the wood used did not receive additional treatments before installation. The photos seen here were taken just a few weeks ago, and no treatments have ever been used on this dock. This wood has withstood 6 years of water, summer sun, and brutally cold and snowy winters. How does it still look so good?

It all comes down to the cellular changes that happen during the thermal modification process. While the science is complex, two key changes make a big difference: the removal of organic sugars (a food source for insects and fungi) and the elimination of hydroxyl groups.

Photo date: March 5, 2025. Installation Date: Spring 2019

Hydroxyl groups (–OH), made of oxygen and hydrogen, are found in the polymers of wood’s cell walls. These groups are polar, meaning they form hydrogen bonds—you guessed it, with water (H₂O). These hydroxyl groups act as sorption sites, bonding with water molecules and causing the wood to absorb moisture.

But during thermal modification, the wood’s cell structure changes, and most of these hydroxyl groups are removed. Without them, the wood becomes hydrophobic—it can’t bond with water. And when wood can’t absorb water, it doesn’t expand, contract, warp, crack, or cup.

And that’s how you end up with beautiful, chemical-free wood dock — even after six years of punishing weather.

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Want to learn more about wood and water absorption? Check out this post: Water Porosity Explained. https://www.thermaprowood.com/post/water-absorption-explained

Want to build a beautiful, long-lasting dock, or have questions you want answered about thermally modified wood? Then give us a call or email sales@thermaprowood.com.