How is wood pressure treated? And today's wood preservatives

Pressure treatment is a process that forces wood preservatives or fire-retardants into the wood. This process is considered the best and most effective method to extend and preserve timber life. Preservatives protect the wood from attack by wood ingesting insects; like termites, and wood rot caused by fungal decay. Fire-retardant treatments help the wood to quickly char when exposed to flame, reducing smoke generation and flame spread.

The pressure treating process is used to treat various wood species according to end-use categories standardized by the American Wood Protection Association (AWPA). The AWPA’s Book of Standards covers preservatives in major use categories such as indoor, outdoor, ground contact, lake and marine uses. Click on the video below to see the pressure treating process from start to finish.

How wood is pressure treated

How wood is pressure treated

For some western wood species, incising is a common process where the wood is resistant to preservative penetration, but the preservative will penetrate along the grain. These wood species are prepared by creating small incisions into the wood prior to the pressure treating process. Check out this two-minute animated video on the treating wood process for western species.

Treated Western wood species

Today's wood preservatives

n a recent article, "What is pressure-treated lumber, and how does it forestall decay?" in Chemical and Engineering News’ March 7, 2022 issue, writer Craig Bettenhausen explains, "Old wood-preservation chemistries have fallen out of favor, and new ones are in the works. But most wood used outdoors by consumers today fights off fungi and insects with these mixtures. Copper is a broad-acting fungicide and insecticide, azoles kill fungi, imidacloprid kills insects, and dichlorooctylisothiazolinone (DCOI) kills fungi and bacteria."

DCOI is also the active ingredient in Ecolife®, a non-metallic preservative used in residential decking and other above ground applications since 2008. In 2018, Viance introduced an environmentally advanced preservative, UltraPole® NXT with DCOI, for wood utility poles for the growing infrastructure market. Penta or PCP (pentachlorophenol) has been a popular preservative for wood utility poles since 1936, but production of the chemical in Mexico and its export to the US for the treatment of wood, ended in December of 2021 effectively making it unavailable worldwide. On February 4, 2022, EPA issued a final registration review decision requiring the cancellation of PCP. Existing stocks of penta can be used to treat wood until February 2027. In accordance with the Stockholm Convention on Persistent Organic Pollutants, production of penta has been banned in the EU since 2019. UltraPole NXT is not a persistent organic pollutant or a restricted use pesticide and was developed as an alternative preservative to replace penta.

More on Preservatives
More on the Pressure Treating Process