How Is Pressure Treated Wood Made?

pressure treated wood and its benefits

Pressure treated wood has been around for more than 70 years after being introduced in the 1960s. When it was first brought into the market, the product was revolutionary. Wood that would naturally suffer termite infestation or decay over a short period of time was made to last much longer with this technique.

Despite the presence of creosote, a derivative from distillation of tar, which was used as a preservative for wood, pressure treatment was still a preferred option because it was less messy and safer. However, although pressure treated wood has been in the market for a long time, many people still don’t know about it.

In this article, we highlight everything that you need to know about pressure treatment of wood, its uses, benefits, process, and drawbacks.

What Is Pressure Treated Wood?

Pressure treated wood is a kind of lumber that is processed by applying a vacuum which serves to inject preservatives as well as fire retardants into the wood. By nature, wood is a material that can degrade and decompose. It is susceptible to fire and insect infestation which can limit the use of this material in various aspects of construction or other industries. Wood has its benefits too but the durability disadvantage is too large to offset.

However, modern techniques like pressure treatment have made it possible to eliminate many of the flaws that wood carries. Applying pressure and chemicals to the wood increases the fire resistance capabilities of the wood while at the same time provides the material other advantages too. Pressure treated wood is also better at repelling insect infestation along with fungal decay making it more suitable for outdoor uses.

How Is Wood Pressure Treated?

Pressure treatment of wood involves several steps. Firstly, the treatment facility orders wood from suppliers. The common types of wood that can be pressure treated include Douglas Fir, Southern Yellow Pine and Western Red Cedar. When the wood arrives at the treatment plant, it is checked for moisture. Wood with a high moisture content doesn’t provide effective penetration to the chemicals which makes this step extremely important.

If the wood is found to contain high traces of water, it is put in a kiln to dry. After this the treatment process can begin. Giant forklifts move the wood onto a conveyor that slides them into a large steel container also known as the vacuum pressure vessel. The giant cylinder-shaped jar is then sealed as the process begins. An industrial vacuum pump attached to the cylinder sucks out air inside the container. The process also includes pulling out air from the wood itself.

Next, the cylinder is flooded with a preservative solution that contains various properties. This mixture of chemicals is designed to provide the wood with greater durability and strength. Once the container is filled with the solution, pressure is applied once again to force it deep within the structural elements of the wood. The number of times this process is repeated as well as how much pressure is applied depends on the retention level needed and the type of wood that is undergoing treatment.

Once the particular cycle is completed, the pump drains out excess solution from the container which is saved for the next cycle of treatment. The freshly treated wood is placed on a drip pad for 24-48 hours in order to allow any solution dripping out to filter and drain away preparing the material for use. Once this is done, the wood is ready to be used for different purposes including construction and numerous others.

The Chemicals Used in Pressure Treatment of Wood

There are a number of chemicals that are used in the treatment of wood. Most of these elements are EPA approved and listed on their website. The most common chemicals belong to a class called isothiazolinones. Creosote is one of the oldest materials that has been used in the process and although it is safety approved for residential use as well, it is quite messy and leaves residue. More modern materials have however, been developed for use in pressure treated wood.

These chemicals include Alkaline Copper Quaternary (ACQ), Borates, Copper azole, copper naphthenate and Polymeric betaine. ACQ is currently the most widely used in the industry as it provides the best results in terms of giving wood specific resistance capabilities. It is effective in boosting the capacity of wood to resist insect infestation, especially termites. The overall results from the ACQ are long lasting enabling wood to last for a good 30+ years.

Reasons to Pressure Treat Wood

There are many reasons to pressure-treat wood. The highest on the list is to increase its capacity to resist decay due to natural elements. Wood is a beautiful material for construction and is used both on the interior and the exterior of the home. However, over time, it can come under attack from termites and fungus which not only ruins the aesthetic but also the structural integrity of the material. As a result, many people shy away from using wood for flooring, roofing, or siding in homes.

Wood is also prone to fire and bending under extreme temperatures. The material is porous which allows moisture to seep in and damage the frames. Pressure treated wood has increased resistance against all these elements which makes it more suitable for use in construction. Wood that has been through the process of pressure treatment can have varying degrees of resistance depending on how long it has been in the vacuum and what chemicals were used to preserve it.

Benefits of Pressure Treated Wood

Before we dive into the advantages that come with pressure treated wood, it is important to note that not all wood acquires the same capabilities after the process. That being said, the biggest benefit of treating lumber with pressure is to increase its resistance against moisture and fungus. Simultaneously, wood also becomes insect resistant after treatment which ultimately means that it will last longer in various applications across diverse industries.

Pressure treated wood also has greater resistance against fires and heat. Wood can catch fire quite easily which makes it hard to use in areas that suffer from extreme weather or seasonal wildfires. After pressure treatment though, it can become more robust and resilient. Wood after treatment can also be cut in more sizes than it normally would, providing the ability to build a wide variety of structures.

Disadvantages of Pressure Treated Wood

Pressure treated wood has numerous benefits in terms of durability and life but there are an equal amount of drawbacks to it as well. First and foremost, the chemicals that are used in the treatment, despite being EPA approved, are not suitable for indoor use. This type of wood is absolutely not recommended for use in kitchens and especially in items where food preparation is involved like cutting boards etc.

Wood that has been pressure treated is also costly and although it is worth the extra cash, the price difference can make it unaffordable on many budgets. Wood that undergoes treatment is placed on a drip pad for 24-48 hours but it can take the material between 3 and 6 months to completely dry which means that during this time it is damaging to one’s health and the environment because of the leaking chemicals and odor that they exude.

Where Can Pressure Treated Wood Be Used?

The application and use of pressure treated wood is mostly outdoors. The properties that the material obtains including fire, insect and moisture resistance are more relevant on the exterior of homes. Contractors and homeowners frequently use this type of wood for siding, roofing, garden docks and a variety of other purposes. This is due to the fact that it can last much longer while also providing a safer environment to the inhabitants of the home.

Other places where pressure treated wood is used includes mail boxes, decks, swing sets, landscape ties, oceanside boardwalks, residential building foundations and picnic tables to name a few. There are building codes and regulations surrounding the use of pressure treated wood and for builders as well as homeowners, it is important to take these into consideration before putting this type of material into their construction projects.

Frequently Asked Questions

Pressure treated wood is not new. It has been frequently used in construction over the years but there are still a lot of questions that lurk in people’s minds when it comes to this material. People are often confused between the advantages and disadvantages of pressure treated wood which means that they remain skeptical about whether to use this product in construction of various properties or not.

Here are some of the most common questions that arise in people’s minds when it comes to pressure treated wood. Pressure treatment involves a lengthy process with lots of chemicals which provides it with various benefits but at the same time brings drawbacks as well. This can be the determining factor for most people when deciding whether to pick this type of wood or not.

Can Any Type of Wood Be Pressure Treated?

In general, yes! Any type of wood can be pressure treated as long as it has a soft texture. The most commonly used wood is southern yellow pine which is ideal for the process as after the treatment, it can resist decay, rot and termites. The pressure treatment process can work on many different types of woods which is crucial to enhancing the features of the material especially when it is used in outdoor projects in construction.

There are different types of woods that are used for pressure treatment but still the capabilities that they obtain can differ. Typically, pressure treated wood is available in three different types which include above ground, ground contact and marine lumber. The first type is prone to leaching out chemicals which makes it only suitable for use above ground and when insect resistance is the main concern. Marine lumber is used for docks, seawalls, and other seaside locations as it is resistant to moisture.

What Is the Difference between Pressure Treated and Normal Wood?

Pressure treated wood is not stronger than regular one. The only difference is in terms of resistance against various elements. Normal wood is susceptible to a lot more damages including rot, decay, termites as well as other insects. It can also bend under pressure or heat but pressure treated wood doesn’t. Shrinkage does occur during the treatment process but that is in terms of overall size and not in bending of the wood.

The biggest difference however between pressure treated wood and normal ones is the ability to resist moisture and fire. Depending on the type of treatment that the wood undergoes, it can become fire retardant which means it won’t catch fire very easily as opposed to normal wood. The same also goes for other types of resistance for insects and biodegradation. The process of pressure treatment also allows manufacturers to add one specific capability to the wood while eliminating the rest.

How Does Pressure Treated Wood Differ from Engineered Wood?

Engineered wood and pressure treated wood are two very different products. Engineered wood is a composition that involves other materials like PVC only to provide a rustic feel without the disadvantages of wood. The layers within engineered wood can vary based on the manufacturer but it isn’t completely made out of lumber which allows it to be more resistant to many elements by retaining the look of wood overall.

Pressure treated wood on the other hand is totally natural with no additional layers of materials within it. This type of wood simply undergoes pressure treatment through air vacuum and infusion of chemicals to ensure that the disadvantages of natural wood are eliminated. Both pressure treated and engineered wood have similar characteristics and benefits but the latter doesn’t have many of the drawbacks of pressure treated wood.

Is Pressure Treated Wood Toxic?

It is a widely held belief that pressure treated wood is toxic and although it has been noted that this material is not suitable for indoor use, overall it is safe and not hazardous. The materials used in the treatment process are EPA approved to make sure that they don’t pose a threat to health or the environment. On top of that there are regulations to follow for its use which means that applications of pressure treated wood remain risk-free.

Before 2003, pressure treated wood was infused with a preservative that contained traces of the harmful chemical arsenic but the use of this substance was eliminated from the industry. The wood available today is safe and many contractors make use of it regularly to ensure that the structures are more rigid as well as resistant to natural elements. From children playhouses to raised garden beds, pressure treated wood is used almost everywhere.

Does Pressure Treated Wood Change Color?

Pressure treated wood does change color and is mostly green because of the chemicals that it is laced with. If you find wood that has a light greenish hue, you can tell that it has been pressure treated. When preservatives are forced into the wood, they also leave their color on the timber and most manufacturers can cover it up by painting or shading the wood with other colors. This is usually effective in hiding the unusual color of the pressure treatment chemicals.

Wood that undergoes the process of treatment absorbs green color but over time, it can turn gray. This happens after exposure to sunlight and other natural elements because of copper within the wood. As wood dries whether it is on its own or due to direct sunlight, the copper will react and cause discoloration. These changes though don’t impact the safety of the wood in any way and the material remains safe for use throughout the industry.

Can Pressure Treated Wood Be Stained in Any Shade?

Indeed, pressure treated wood can be stained with various dyes to give it different shades. The combination of colors can differ since the chemicals infused into the wood leave their own hue but overall, this type of wood remains available in all kinds of colors. Pressure treated wood is common in most construction projects and as such it can come in a variety of different types because of the applications that it entails.

Pressure treated wood is only different from normal wood in the case that it is resistant to various factors like fire, insects and rot. Besides this, the textures, shades and patterns of wood can remain the same especially when it comes to outdoor use. Manufacturers go to extreme lengths in making sure that the wood retains its original aesthetic even after being pressure treated to overcome many of its drawbacks.

Are There Any Precautions to Consider When Working with Pressure Treated Wood?

Generally, there are not many precautions to consider when using pressure treated wood. In 3 to 6 months, the material becomes completely leak free and doesn’t give off fumes or other harmful substances that can be dangerous to human health or the environment. The pressure treatment process is strictly regulated which is another step in making sure that the product is safe for use in construction of various structures.

However, there are building codes and guidelines that need to be followed with respect to pressure treated wood. These rules can differ based on the state in which the project is being constructed. Homeowners and contractors must bear this in mind. Moreover, the disposal of pressure treated wood is very different from that of normal materials because it can be dangerous if proper procedures are not followed so this is another thing to be wary of.

Importance of Professional Installation

Given that pressure treated wood can be challenging to work with because of the chemicals used during the process, it is crucial to have professional contractors install it. The process of pressure treatment on wood can leave it full of various substances that take at least 3 months to dry off completely. Most wood in construction projects can come into use earlier than this which adds significance to professional handling of the material.

When picking a building company or contractor, it is important to make sure that they have worked with pressure treated wood before. The significance of prior experience cannot be overstated  because of the type of material that is being used. A company may claim to have done similar projects before but homeowners have to go the extra mile in performing proper research before entrusting the service provider with the responsibility to build a project with pressure treated wood.

A professional installation company will not only know how to handle the wood appropriately but also find the most effective places for it to be put in place. These contractors will also advise you regarding any precautions that you need to take after the installation has been completed especially if the wood is used in places where human contact is inevitable. It is always better to be safe when working with materials that are beyond naturally available iterations of the same.


Pressure treated wood has been a favorable material for foundations and exterior structures of homes for many years because of the properties it has. Natural wood has its own benefits in terms of visual appeal but there are a lot of disadvantages that come with it. Pressure treatment is the ideal solution that the industry initiated a long time ago to make wood more resilient towards decay, rust, insects, and fire.

The use of various chemicals in the process make people careful regarding the use of pressure treated wood but with extensive safety protocols and other checks, manufacturers make sure their products remain free of risks. The proportion of hazards to health and the environment are minimized during the process while also maintaining overall integrity of the wood. All in all, the wood that is obtained after pressure treatment is worth the added investment during construction.

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