Treated Wood: Everything You Need to Know About Preservation

Treated wood seems like a simple concept.

The truth is, many variables affect the type and amount of preservatives used to protect the wood from the elements and ensure it has a long, useful life.

Understanding the different factors involved makes you well-informed, allowing you to make the best decisions for your business.

Let’s dig a little deeper into the world of treated wood.

Treated wood associations

There are a variety of chemicals that are used for preserving and treating wood.

Because these chemicals are registered pesticides, they’re subject to regulation by the United States Environmental Protection Agency (EPA). 

A different agency – the American Wood Protection Association (AWPA) – creates standards that determine how the chemical formulation of wood preservatives are to be used when preserving a wood product.. 

The wood treater then uses these standards when preserving wood products. To ensure the wood product is preserved to the standard’s guidelines, the treated wood is inspected on a regular basis by third-party inspectors.

Categories of use for treated wood preservatives

What are the treated wood preservative protection categories?

The treated wood preservative protection categories are:

  • Rot due to fungus
  • Decay from termite infestation
  • Exposure to outdoor elements
  • Interior use
  • Exposure to marine organisms
  • Docks and/or pier pilings
  • Fire Retardant Treated Wood

Untreated wood is vulnerable to a whole host of environmental factors that will cause it to decay and break down more quickly.

Treating wood doesn’t have a one-size-fits-all solution. Formulations are made for specific categories of use.

For example, wood that is located in the interior of a building will need a different treatment than lumber that’s being used outdoors, exposed to the elements. 

Specific treatments are also required to prevent rot due to fungus or termites and to protect against marine organisms when the wood is used for dock or pier pilings.

There’s also a category for Fire Retardant Treated Wood (FRTW).

Types of preservative treatments for wood

What are the types of preservative treatments for wood?

The types of preservative treatments for wood are:

  1. Topical or surface treatment
  2. Pressure-impregnated

There are two main categories of preservatives for treating wood. Let’s take a closer look at them.

1. Topical/surface treatment

This type of treatment only protects the surface of the wood and it’s applied by spraying, dipping, or brushing. 

While topically treating wood will protect it from the elements, it isn’t as effective at preventing insect infestations or rot.

2. Pressure-impregnated treatment

What are the categories of pressure treatment for wood?

The categories of pressure treatment for wood are:

  1. Waterborne
  2. Creosote
  3. Other Oil-borne

This is a much more involved and thorough process than topical treatments.

The process is performed in an autoclave where chemical preservatives are infused into the wood itself, going deeper than just the surface.

Pressure-treating wood involves impregnating the wood with the preservatives in an autoclave, removing the excess chemicals, leaving behind the precise amount needed to protect the wood.

The AWPA sets the standards for how much of the preservative chemicals the wood should retain after treatment, in accordance with its intended use. 

These regulations are continuously reviewed by the AWPA’s technical committee to ensure the chemical preservative levels are appropriate and that the formulations are working as effectively as they should.

Pressure treatment of wood is divided into three categories:

  1. Waterborne treated lumber. This method of treating wood is for lumber that’s being used in industrial, commercial, or residential settings.
  2. Creosote. This agent is used for treating wood used for guardrail posts, railroad ties, and any marine structures.
  3. Other Oil-borne treated lumber. This treatment method is for a very specific purpose – utility poles and cross-arms.

List of preservatives used for treated wood

Here’s a breakdown of specific preservatives used in treating wood.

  • Alkaline Copper Quaternary (ACQ)
  • Copper Azole (CA-B, CA-C)
  • Copper Naphthenate (CuN)
  • Ammonia Copper Zinc Arsenate (ACZA)
  • Creosote
  • Chrome Copper Arsenate (CCA)
  • Pentachlorophenol, also known as Penta (PCP)
  • Micronized Copper Azole (MCA, MCA-C)
  • Inorganic Boron (SBX)

Know your treated wood

Understanding the types of preservatives used for treating wood, the categories of protection, how the processes work, and which chemicals have used all work together to give you a complete picture of treated wood. An easy method for doing this is to use the AWPA Use Category System

The more you know, the better choices you can make for the good of your business.

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