How Does Pressure Treated Wood Work?

How Does Pressure Treated Wood Work?

April 21, 2023

How Does Pressure Treated Wood Work?

Pressure treated wood is an ideal building material for outdoor projects like decks, fences, garden beds, and other wooden structures. It has a chemical preservative that protects it from water damage, mold, and insects. The wood is treated by a process that involves injecting the preservatives deep into its cell structure. This extends the lifespan of the wood by decades and prevents it from rotting or sustaining insect infestations.

Chemical Preservatives

When you buy pressure treated lumber at your local home store, you will see a tag stapled to the end of the board that says “treated” or “preserved”. The wood has been treated with a chemical to prevent rot caused by insects and fungus. This type of treatment is commonly used for lumber that will be exposed to the elements, such as decking and fences. It also protects marine structures such as dock and pier pilings. And unlike water-borne preservatives, this type of treatment is not toxic to the environment and human health!

Vacuum Pressure

When wood is shipped to a pressure treating plant it is placed on a tram and moved into a large steel cylinder, called a vacuum pressure vessel. This treatment process enables deep penetration and retention of preservatives to protect the wood against rot, insect infestation and termite damage. Wood is then subjected to a series of pressure and vacuum cycles within the cylinder, which forces the preservatives into the wood’s cells. The chemical bond forms between the preservative and the cellular structure of the wood, making it resistant to decay and attack by insects.


Pressure treated lumber is a little different than standard wood in that it takes longer to dry. It does this because of the chemical treatments and the water it takes to clean. It is important to let it dry before using it for framing or painting, because wet wood is heavy and slippery. This makes it difficult to measure, fasten, and paint it correctly. To help speed up the drying process, kiln-drying is recommended. This can take one to eight weeks, but is much faster than air-drying. Alternatively, if you want to avoid the long drying time, you can lay out the wood flat and stack it in a crisscross pattern to allow it to dry quickly during warm weather. However, it is not a good idea to leave pressure treated lumber out in the rain. This can cause the lumber to warp and splint. You should also check the wood regularly for moisture content.

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