How to Tell If Wood Is Pressure Treated? Useful Tips To Identify

In a quest to ensure that wood lasts forever or at least for many years, a technique had been developed by Dr. Karl Wolman less than a century ago. This process is known as pressure treatment and involves the injection of a chemical into the wood.

The wood piece is placed into a large cylindrical tank which has been depressurized to remove all air. The preservative fills up the tank with the wood under high pressure. The wood absorbs the preservative and is therefore protected from mites, fungus, vermin, and insects for many years. But, how to tell if the wood is pressure treated? Let’s try to understand.


There are a number of ways that can be used to find out if a wood is pressure treated or not. Let’s find out.

Ways to Tell If Wood Is Pressure Treated

Chromated Copper Arsenate (CCA)

This process started was introduced in the 1930s when chromatid copper arsenate chemical preservative was injected into the wood to give it a greenish hue.

This type of wood is however not much in use nowadays and nor is this treatment done due to various other modern safer wood treatments that are available today. Usually, very old wood may be exposed to such treatment.

Alkaline Copper Quaternary Wood

A more modern type of pressure treated wood is Alkaline Copper Quaternary Wood or ACQ. ACQ is a far better option than CCA as it’s safer and greener. It’s a water based preservative which can fight against wood infesting organisms and also protect against weathering. The greenish hue is acquired during the production process.

No Color Tinted Wood

If the wood has no color other than its natural color, it’s a possibility that it might not have been treated. If the wood has a grayish color, a cut can be made into the middle to see if it’s yellow or white, which means no treatment has been done.

Easiest Way to Find Out If Wood Is Pressure Treated: Just smell the wood and see if you are getting an oily smell. Is the wood smells natural, then it’s more likely to have not been pressure treated.

Toxicity of the Treatments

Since the 1940s, pressure treatments have evolved enough to move out from toxic chemicals to safer and eco-friendly ones. The previous treatments like chromate copper arsenate protected the wood from moisture by injecting chromium and copper.

However, these were quite toxic by nature. Therefore, the wood that has been pressure treated with CCA has been banned for domestic uses like garden furniture, benches, play ground equipment, picnic tables, patios and so on which may affect humans as well as other animals.

Identification Stamping

In modern time pressure treated wood is stamped to indicate how much ground contact levels can be achieved. Wood that is stamped L P22 means it contains arsenic, therefore it’s most toxic and can be used for applications involving direct contact with the ground.

Slightly lesser toxicity can be indicated by a stamp L P2 and may not be recommended for direct contact with the ground. FDN means the wood is designed as a floor foundation material and therefore, it is one of the safer types of pressure treated wood. 

Safer Variety of Pressure Treated Wood

One of the safer varieties of pressure treated wood of recent times is the Borate which can be good for both interior and exterior use. Borate being a natural mineral, it protects the wood from bugs, fungus and other organisms that destroy wood.

Borate is suitable for all types of uses like two by fours, plywood, beams, and posts. Borate stamps are usually not standardized and may vary. For example, they might have Tim Bor, Hi Bor or just Borate printed on it. 

  • Green patina
  • Acquiring a fact sheet

Usually, borate treated woods are hard to tell apart from untreated ones. A greenish patina which is brighter than the old CCA treated ones is applied on borate treated wood to make it distinguishable.

About chemicals used in Pressure Treatment

CCA has been banned due to the toxic levels and existing CCA treated woods are required to be treated with precautionary oil at regular intervals. This precautionary oil is a sealant which locks the arsenic chemicals that are highly dangerous.

Recent pressure treated woods also need to be locked with a sealant which protects from weathering and corrosion. Therefore, pressure treatment and sealant work hand in hand as the former save the wood from internal decay the latter saves the exterior.

If the wood dries too fast, it causes warping which is also prevented by a sealant. After being allowed to dry for few months to enable proper adhesion the wood can be painted and stained as well.

Where to use Pressure Treated Wood

Pressure treated wood is more suitable for outdoors than indoors. Indoor wood being more in contact with humans and pets, it’s better to leave such wood untreated.

The saw dust from the wood that is pressure treated can be an irritant to eyes, skin, and nose. The leaking chemical preservative may not be good for indoors but outdoor wood should be protected using pressure treatment. Indoor wood can be properly selected to be prevented from insects and mites.

Usually, pressure treated wood is recommended for places where insects are difficult to avoid and ground contact is required. If the wood in question comes in contact with humans, animals and food items, then the safer version of pressure treatment stamps must be sought.

Once you get a proper understanding of the compounds and chemicals used a decision can be made which type of pressure treatment you will consider for various areas of use.

Alternatives to Pressure Treated Wood

There can be enough reasons to avoid using pressure treated wood and yet require safety measures to ensure the longevity. Below are some ways in which you can seek some effective alternatives.

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    Use naturally resistant woods that prevent rot and insect damage. Redwood and Red Cedar are examples of such naturally resistant woods which can be used if you wish to avoid pressure treated wood.
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    Certain plain oil-based exterior grade paint can be used to protect the wood that is used outdoors. The enamel will protect against water and also insects getting into the wood.
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    A natural whitewash using lime and water mix can be used to protect the wood. It’s an old method of wood protection and it may require you to wear gloves to protect your hands while applying.

Wrapping Up

We hope that the above article would have provided you enough insights on how to tell if the wood is pressure treated and its alternatives.

What are your views on this? Do you have any queries? Do let us know in the comments. Don’t forget to share this article with your friends and family!

Abigail Jones

Hi, I'm Abigail. I like spending time tearing my house apart and putting it together back again. Join me on home improvement tutorials, tips on my blog.

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