There’s a Superhero Beneath Your Feet

Imagine a trail dipping below a steep valley edge surrounded by lush, verdant greens. A brook chatters below and in its soft watery tones invites hikers to a moment of relaxation and communion. The breeze is soft and sweet as the leaf canopy dances in unison overhead. It is idyllic and accessible because of the wooden boardwalk solidly supporting each who visit this natural wonder.

This boardwalk and others like it can be found in many natural areas. But it is made possible by pressure-treated wood, a building material that when processed with the correct preservatives, often outlasts and outperforms durability estimates and usefulness before it can biologically deteriorate.

Since wood became one of humanity’s most popular building materials thousands of years ago, combating biological decomposition has been its greatest challenge. However, pressure-treatment can help overcome these obstacles. Just like finding the appropriate outdoor gear to best live-in and enjoy one’s environment, pressure-treating creates a barrier to weather, destructive insects, moisture, and aging.

In December of 2019, Forest Products Laboratory (FPL) researchers Stan T. Lebow, Juliet D. Tang, Grant T. Kirker, and Mark E. Mankowski published, “Guidelines for Selection and Use of Pressure-Treated Wood.” The publication examines appropriate uses for waterborne and oilborne preservatives considering building location, use, and wood species. In addition, they examine how well a preservative penetrates and retains for durability without structural damage.  

So what exactly is pressure-treatment?

First, a pallet of lumber is placed in a cylindrical vacuum chamber and air is sucked from wood cells. Then while maintaining the vacuum pressure, the chamber is filled with liquid preservative. When the lumber is totally submerged, the chamber is flipped from vacuum to pressure. Pressure bears down on the lumber and pushes preservative into the previously emptied wood cells. Once the wood is saturated, the pressure is released and the chamber is emptied. A final vacuum is applied to remove excess liquid and the treated lumber is placed on a drip pad in a covered storage facility.

Diagram of the pressure treatment process.

Pressure-treatment is essentially the superhero solution for wood.

Any super-performer worth their salt has a team of experts supporting them, and FPL researchers have been studying the most effective ways to preserve wood since the Lab opened its doors in 1910. From a state-of-the-art pressure treatment pilot plant to ground-contact stake testing, researchers conduct meticulous tests so quality is at the highest standard.

Where can you find pressure-treated wood?

Pressure-treated wood can be found in the utility poles supporting our electricity distribution to the railroad ties that pave our railway systems. Decks, playground structures, and outdoor furniture provide years of enjoyment thanks to wood preservatives. Bridges often incorporate glue-laminated pressure-treated timbers because of their high strength and ability to span long distances. Seawater marine piers use pressure-treated lumber in their piles because of the unique qualities some wood preservatives have for repelling aggressive marine borers.

And of course, pressure-treated wood is found in the boardwalk trail below your feet.