Treated lumber is a popular building material that has played a key role in the construction of many of our structures in the Pacific Northwest. In this series, our good friend and expert in pressure-treated wood, Dennis McWhirter of Exterior Wood, answers common questions about treated wood. In this episode, Dennis is sharing a little bit about the history of pressure-treated wood's chemical makeup.
Why is wood chemically preserved?
There are basically two things that can happen to wood: either it burns or it rots. Early in human history, people learned you can retard or reduce both of these outcomes by treating the wood with various additives.
How was wood preserved throughout history?
In the time of Ancient Greece, people used olive oil to preserve wood. In time, people began to use tar to treat wood, as well as a variety of oils. In the early 1950s, the treatments were primarily industrial-type treatments. They were very messy, and most people didn’t want to use them in residential construction.
What wood treatments have been used in recent history?
In the late 1970s, chromated copper arsenate (CCA) became popular. The CCA treatment is made of copper, chrome, and arsenate, and it was a very effective product. In fact, it’s still used today for some industrial and agricultural uses, including pole-barn material. In the early 2000s, CCA was replaced in residential uses with products like alkaline copper quaternary (ACQ) and copper azoles, believed to pose less risks to health and the environment because they didn’t include arsenate. Copper is a natural ingredient that’s found in a lot of the things we use, and azoles are organic fungicides.
Though the methods used to treat wood have changed over time, wood continues to be one of our greatest renewable resources—and at Exterior Wood, we think that’s worth preserving.
Read the first installment in our pressure-treated wood series, where we unpack how pressure-treated wood is made. Then, check out a detailed summary of manufacturing pressure-treated lumber. Stay tuned for the rest of this series, as Dennis answers all your pressure-treated wood questions.