Pressure treated wood is used for a lot of exterior projects because it is hard-wearing and resistant to moisture. You will often find it used for decking or wooden fences, for example. But when you are using wood, it is important that you are able to tell whether it has been pressure treated or not, and which chemicals have been used to treat it.
Check the color, the end tag, and the stamp to give a quick indication of whether it is pressure treated or not. The smell can be an indication too, but only when the wood is relatively new. If you are still unsure, you can use a test kit.
There are potential dangers involved with using pressure treated wood, especially if you are sanding it or using it inside your home, so it’s important that you know exactly what type of wood you are using. This article will help you determine whether the wood is pressure treated or not.
What is Pressure Treated Wood?
As the name suggests pressure treated wood is wood that has been treated with certain chemicals. The wood is first put inside a vacuum chamber and then exposed to various chemicals. The pressure created by the vacuum forces the chemicals into the cells of the wood.
The chemicals used depend on what type of wood it is and where it will be used, but most commonly, chromated copper arsenate (CCA) or alkaline copper quaternary (ACQ) are used. These work as preservatives and kill any harmful microorganisms such as fungi and bacteria that come in contact with the wood. They can also make the wood more resistant to moisture to prevent rot in the future.
In the past, CCA was used for all pressure treated wood but there are concerns about potential health risks because of the presence of arsenic. As a result, ACQ is more common, but CCA-treated wood is still used for industrial purposes. If you are choosing wood for residential projects, you need ACQ-treated wood.
Although CCA and ACQ are the most common, there are other chemicals used to treat wood. Borates are used because they are less toxic than CCA and they don’t color the wood. However, their water-soluble nature makes them more likely to leach out of the wood in rainy climates. Micronized Copper Azole is another environmentally friendly chemical, but it is more expensive.
Why Use Pressure Treated Wood?
There are a number of benefits to using pressure treated wood.
It is very durable and will last a long time. It doesn’t warp, crack or rot so it can be used for exterior applications such as decking or fences.
It resists insect infestation and termites so it provides good protection against damage from these pests.
If you are using the wood on the ground, either above or beside the ground, it prevents moisture from seeping in and rotting the wood.
Pressure treated wood will last a lot longer than non-treated wood, even if you do not stain or seal it. It is also cheaper than buying non-treated wood and treating it yourself. On average, pressure treated wood will last around 10 to 15 years when used for things like decking or fences.
Although pressure treated wood is more resistant to moisture, it is not completely waterproof so you need to take precautions when using it. Wood will absorb water if the protective coating has been damaged or removed so consider using a sealer on pressure treated wood after a few years to keep it in good condition.
What are the Different Types of Pressure Treated Wood?
When you are choosing pressure treated wood it will be broken down into different categories based on the retention level. The retention level describes how much chemical is left in the wood when it is dried. The more preservative that is left in the wood, the more resistance it will have to moisture, mold, and mildew.
1. UC3-treated wood
UC3-treated wood has a preservative of at least 1.75 pounds per cubic foot and it can be used in any application provided it’s not being exposed to extreme moisture or humidity levels. This type of pressure treated wood is commonly used for decks, fences, playground equipment, landscaping timbers, etc.
2. UC2-treated wood
UC2-treated wood has a preservative of 1.0 to 1.75 pounds per cubic foot and it can be used in exterior applications but not ground contact. For example, you could use it for decking, fences, playground equipment, etc. but not as posts or landscape timbers.
3. UC1-treated wood
This type of pressure treated wood has a preservative between 0.5 and 1 pound per cubic foot and it cannot be used for ground contact or exterior applications. For example, you could use it for shed flooring but not anything that will come in direct contact with the soil such as landscape timbers.
There are other gradings, but these are for marine use or industrial applications with extreme conditions, so you don’t need to worry about them for any jobs that you are doing in your yard.
Lumber will also be graded on strength, but this is determined by the lumber itself rather than the pressure treating process.
How to Tell if Wood is Pressure Treated?
1. The Color
Pressure treated wood varies in color depending on what it has been treated with. The chemicals that are put into the wood react with the sap and the air, causing them to oxidize. This then creates different colors, depending on which chemicals are in the wood.
- CCA
Wood that has been pressure treated with CCA will have a green tint to it. This is the easiest type of pressure treated wood to spot simply by looking at the color.
- ACQ
Wood that has been pressure treated with ACQ will have a brown or tan color. However, it is important that you don’t mistake wood that has been painted or stained with wood that has been pressure treated.
- Borate
Wood that has been pressure treated with Borate retains the natural color of the wood. This makes it more difficult to determine whether the wood has been pressure treated or not if Borate has been used.
2. Read the End Tag
Most pressure treated wood will have a tag attached to it that indicates what type of preservative has been used. It also tells you what the most suitable end-use for the wood is (above ground, ground contact, etc.) Reading the tag on new wood should tell you everything you need to know.
3. Smell the Wood
New pressure treated wood will have a chemical smell to it, but non-treated wood doesn’t. So, smell the wood and see if it has a natural odor or not. Bear in mind that the chemical smell will dissipate after a while, so this is not a foolproof method and it only works well on wood that has been treated recently.
4. Test the Wood 
If you are unsure about whether the wood is pressure treated or not, you can get test kits like this Arsenic Wood Field Testing Kit. These can be useful if you have old wooden fixtures that you need to work on but you don’t know if they were pressure treated or not. The quick test will show you whether there is arsenic present and how much.
5. Is it Stamped?
Pressure treated wood should have a stamp on it too. This contains information about what kind of treatment was used. Look for the initials ‘PT’ to indicate that the wood has been pressure treated. It may also have ‘GC’ for ground contact and ‘AG’ for above ground.
You may also see LP-22, which indicates that the wood is designed for direct contact with the ground, and likely contains arsenic. LP-2 designates a less toxic pressure treatment process. FDN stamps mean that the wood is designed for use as a floor foundation material.
The stamps on wood that has been treated with Borate are less consistent. You may see the word Borate printed in full or it may say ‘Tim-Bor’ or ‘Hi-Bor’ on it.
Usually, if there is a stamp on the wood, you should get a good indication of whether it is pressure treated or not and what chemicals have been used in the process.
Why is it Important to Tell if Wood is Pressure Treated?
Whether you are working on an old home that has pressure treated wood or you are putting new pressure treated wood in your own yard, it is important to know what kind of chemicals have been used so that you can take the appropriate precautions.
For example, certain types of preservatives contain arsenic, and they are only safe to use in certain situations. If you are using them in areas that you will regularly come into contact with, you could do damage to your health. You don’t want to use CCA-treated lumber to build a deck.
Equally, you need to make sure that you use the right type of pressure treated wood for the job. If the lumber will be in contact with the ground or exposed to a lot of moisture, you must ensure that it has a high enough retention rating so it does not rot.
What are the Safety Precautions When Dealing with Pressure Treated Wood?
All types of pressure treated wood can be potentially harmful because they contain strong chemicals. As such, you need to be careful when using it. Sanding presssure treated wood can be particularly dangerous as tiny wood particles containing chemicals can be inhaled.
Make sure you wear a mask, goggles, and gloves to protect yourself from the chemicals. You can find more information on how to safely sand pressure treated wood here.
Do not burn pressure treated wood either as the chemicals will release poisonous fumes when burned. It is also a good idea to wash your hands after working with pressure treated lumber because the chemicals can get on your skin.
RELATED: How Long Does Pressure Treated Wood Last?
Final Thoughts
If you are unsure whether wood has been pressure treated or not, you can use some of the methods described above to find out. If it has been treated, try to find out what chemicals have been used in the process. And if you are dealing with arsenic-based preservative treatments or CCA, take all the necessary safety precautions before working with them.
Jamie is the founder of The Backyard Pros. When he was 15 years old he started working at a garden centre helping people buy plants, gardening products, and lawn care products. He has real estate experience and he is a home owner. Jamie loves backyard projects, refinishing furniture, and enjoys sharing his knowledge online.