How Is Pressure-Treated Wood Made?

Good Wood Needs Protection

• Wood is a wonderful building material for its flexibility, strength and aesthetic appeal. Unfortunately, wood also has many natural enemies, as it's highly susceptible to deterioration from pests, moisture and microbes. In order for wood to last a long time without losing its strength, it usually is treated through some industrial process. Pressure treatment is one of the most important and widely used of these processes and is available commercially. Pressure-treated wood used in everything from home construction to power poles.
  
  

Chemical Treatment

• Pressure treatment involves two steps. First, the wood is treated with preservatives. These chemicals make the wood unappetizing to pests and resistant to water. Depending on the wood's purpose, different types of preservatives can be used with varying preservative qualities. Some are water-based, which is generally preferred for wood used in indoor applications where pests are a problem. Others are oil-based, which is generally preferred for wood used in outdoor applications where weather is a problem. Creosote is in a class by itself is especially in seawater.
  
  Some of these chemicals are dangerous to human health, like arsenic and creosote, but in most cases they have been found not to leak out of the wood, making them safe. Newer chemicals have been developed more recently to replace some of the most hazardous preservatives.
  
  

Pressure Treatment

• Next, the wood is placed into a sealed chamber where it is exposed to extremely high pressures. This pushes the chemicals from the wood's surface deep down into the interior. The end result is that the entire wood is protected all the way through, which greatly increases its durability.
  
  There are different grades of pressurization to which the wood can be subjected. The higher the grade, the more deeply and thoroughly the preservatives are pushed into the wood.