Explaining Pressure Treated Lumber

[Posted on Nov 29]
Written by: Aaron Presley

The concept of pressure treatment preservation goes back to the time of World War II when Dr. Karl Wolman formed the inception and attempted to revolutionize a way to preserve lumber over a long period of time. Over the following 70 years, that simple idea and quest it spurred turned into a thriving industry replete with scholarly research, standards of operation and regulations for use, production and safety. Needless to say, pressure treated lumber continues to hold an ongoing place in our society.

What Is Pressure-Treated Lumber?

Pressure treated lumber is wood product instilled with chemical preservatives that protect it against insect infestations, bacterial and fungal growth, exposure to inclement weather and decay, all of which are common occurrences in outside settings.

The key word here is ‘outside.’ Pressure-treated wood is intended for use outdoors. Common applications include decks, bridges, picnic tables, benches, fences and light poles. This means that pressure-treated lumber is never to be used indoors, except when treated with chemicals that are non-threatening to human or animal health, such as boric-based preservatives. In short, the product is specialized to a particular environment.

How Is Lumber Pressure-Treated?

The pressure-treatment procedure is a simple one: A large quantity of precut wood is enclosed in a large cylindrical tank specially designed for the process. The space within the tank is depressurized to expel all air, and a chemical compound floods the chamber where it is forcibly infused into the wood. After a considerable amount of time has passed, the tank is drained and pressurized once again.

The chemical preservatives used, however, are dependent on the kind of wood treated and that wood’s intended purpose. For example, CCA (chromium copper arsenate) and arsenate-based preservatives are used for wood intended for outdoor application where the elements are harsh. Boric preservatives, because of their weak adhesive quality, are reserved for more enclosed, well-protected locations, such as indoor applications (e.g. flooring) where rainwater access is non-existent.

Pressure-treated lumber ensures that integrity and long-life are assured and maintained in a virtually endless variety of scenarios, on both land and sea. Wood, as a natural resource, is essential for many reasons, and so its preservation is unquestionably imperative.