Pressure-Treating Lumber and Lessening the Environmental Impact of Preservatives

Since the day man started chopping down trees and using their wood for building materials, he has searched for ways to make lumber last longer in the presence of weather and insects. In the beginning, lumber was soaked in oil or painted with tar to extend its life. Over time the process and materials used have morphed and have given birth to the processes of pressure treating used today.

Pressure-treated lumber is more durable than untreated wood, it retains its shape better, and it is nearly impervious to damage from insects, fungi, and moisture. This makes building with pressure-treated lumber the only way to go when it comes to wood exposed to the elements or in areas with high humidity or termite infestations.

Technology has advanced a lot since the first days of treating wood with oil or tar to prevent its demise, and most lumber today is impregnated with non-toxic chemicals that are safe for humans and the environment. Additionally, much of today’s pressure-treatment process is automated by large industrial processing plants using massive autoclaves.

Large batches of lumber are placed in each autoclave and then subjected to heat, pressure, and either steam or nitrogen gas to carefully control the drying process. The wood is heated to destroy pest larvae, impregnated with preservatives, and then dried in such a way to make it harder and more impervious to weather or decay.

In addition to autoclaves, lumber is also pressure treated around the globe using a wide variety of other methods, including:

• hot dip baths
• cold dip baths
• painting
• spraying
• bored-hole impregnation
• charring

Lumber is also treated in a process designed to remove all of the sap present in the wood.

Regardless of the process used to pressure-treat the lumber you build with, it’s nice to see preservatives being used that are much more eco-conscious than years past. Gone are the days of treating wood with arsenic and other toxic chemicals and this is great for everyone and the earth.