What is pressure-treated wood?

What is pressure-treated wood?

In the history of humanity, wood has been the best renewable building material. 

In the past, there were only regular woods (natural wood lumber), with no safety chemicals. Such woods tend to get infected by bugs as well as much biological deterioration.

Here is an example of pressure-treated woods

Regular woods can have negative effects if exposed to humid and temperate conditions, as well as water. There comes the need for pressure-treated wood, these woods are usually made to last longer than regular woods. Depending on the chemical used, pressure-treated woods are available in many different varieties.

Why do people mean by Pressure-treated wood?

Any wood which has gone through a chemical process can be called pressure-treated PT wood.

In efforts to increase the durability of regular lumber, it’s treated with some chemicals. In simple terms, pressured-treated woods contain chemicals in it which are absorbed through pressure.

In addition to being durable and less susceptible to decay, insect infestation, mold, and water damage, pressure-treated wood are also more resistant to insects and mold.

Furthermore, these woods can be made into good fire retardants by using chemicals.

Interestingly, there are so many types of all of them, and they have all been treated differently.

What are some grades?

UC1Interior DryBaseboards & framing
UC2Interior WetPlates on the sills and bottoms of walls, damp locations, framing in basements, bathrooms, flooring, baseboards
UC3 AExterior Above Ground, Coated with Rapid RunoffTrim, fascia, and decking are protected
UC3 BExterior Above Ground, Uncoated or Poor RunoffAny wood within 6 inches of soil or vegetation should not be used for shingles, staircases, joists, beams, decking, railings, or fence railings
UC4 AGround Contact,

General use
Woods within 6" of soil, grass, or water, or places with poor air circulation, like fences, decks, columns, retaining walls, and patios
UC4 BGround Contact,

Heavy-duty use
With UC4A plus post-to-ground installation, freshwater and saltwater spray, retaining walls, foundation support, and garden posts
UC4 CGround Contact,

Extreme duty use
Pilings or wood installed directly in the soil, freshwater, concrete, or soil exposed to extreme weather conditions
UC5 AMarine Use, northern waters,

Salt or brackish water
Interacting with and immersing in cold ocean shores, piers, pier walls, beach fronts, pedestrian walkways, & buildings
UC5 BMarine Use, central waters,

Salt or brackish water
Warm ocean waters off California and Long Island, and in the same way as UC5A
UC5 CMarine Use, southern waters,

Salt or brackish water
Aquaria along the Gulf Coast & south of Georgia, as well as in a similar way to UC5A
UCF AInterior Above Ground

Fire Protection
The construction of interior features no contact with the ground, e.g., fire partitions, kitchens, hallways, in addition to stairwell frames
UCF BExterior Above Ground

Fire Protection
Construction outside, surface exposure to water but no ground contact, porches, stairs outdoors, window dressings

How do they differ from regular woods?.

The only difference between pressure-treated wood and regular wood is the use of chemicals. Regular woods don’t contain any chemicals to resist infestation to fight against the process being rotted with time.

On the other hand, pressure-treated contain a lot of chemicals, even when you cut them using a saw you will see visible chemicals emerging out of a piece of lumber. 

Additionally, the color of regular and pressure-treated wood differs. Regular woods have the natural color depending on the species, whereas pressure-treated woods show chemical shadows like greenish, reddish, etc.

How much Pressured-treated woods are toxic?

Pressure-treated woods contain CAA chemicals in a large quantity. Usually, on every cubic foot per wood area, there are about 0.04 pounds of chemicals in it.

This is to say even they’re not toxic at all but the amount of gas they release can harm your lungs when inhaling them for a longer period. Wearing a mask there is a must.

CAA chemicals have raised safety concerns. 

A study conducted by the Environmental Protection Agency found that chemical preservatives, including arsenic, were not leaching into soil or water. 

Those who use CCA-treated wood daily also have no increased cancer risk, according to independent laboratory studies.

How is pressure-treated wood made? (step by step)

To make it simpler to understand here we broke down the process of making a pressure-treated wood. 

It requires some machines like a large steel cylinder, forklifts, and adhesives chemicals.

Step.1 Moisture should be optimal

After ordering pieces of lumber from a factory or mills, the moisture level is the first thing to check. If the moisture level is under %20 it’s considered good-to-go.

Step.2 Putting inside a steel cylinder.

The process of pressure-treating begins when a forklift places the wood on a tram, which moves the wood into a pressure vessel that is adorned with a small hole in the middle. 

After the wood is loaded, the cylinders will be sealed and any air inside the cylinder will be removed by vacuum using an industrial vacuum pump.

Step.3 Pouring chemicals.

Once all the air inside that sealed cylinder has been removed. The lumbers are now flooded with chemicals, then pressure is applied until all the chemicals are fully absorbed by the piece of wood.

Applying these steps a pressure-treated will be ready to ship and to use. 

What are some benefits?

The prices of pressure-treated woods are high for a reason that they can do a lot more than regular woods in terms of rotting they’re the best.

Because pressure-treated wood has been chemically and preservative treated, it is resistant to a wide range of problems.

Here are some of the benefits:-

The ability to resist rot.

One of the main benefits of pressure-treated wood is its ability to resist rot which is common in regular woods. 

Some bacterias like fungi can make this up and by using chemicals this can be prevented.

Protection from insects.

Woods are always prone to get infested by insects. To overcome this problem.

Since the chemicals in pressure-treated wood are dangerous for insects, they are supposed to prevent insects from eating the wood.

Retards the spread of fire.

Some pressure-treated woods are good retards to spread the fire. 

Carpenters now shift to wood beams of pressure-treated woods for this reason as well.

easy to use. 

Wood that has been pressure treated is light, and it can be easily cut with regular saws and adhered to various substrates such as stains and paints.

There is one thing you should keep in mind when working with pressure-treated woods: They release a lot of gas when cut or broken, so wearing gloves, a mask, and other safety gear is recommended.

Can you paint pressure-treated lumber?

The very same treatment that allows pressure-treated wood to last outdoors also poses a problem when painting it. 

A wood treated with chemicals is less susceptible to insects and becomes anti-rot, but it leaves the wood damp due to the absorption of chemicals, which eventually results in the paint peeling off over time.

However, pressure-treated woods can be painted with any adhesive paints, but the durability will not be as much as regular woods offer.

Meanwhile, after some time, the paint will start peeling off the surface due to the already filled pores on the surface, unlike regular woods which have open pores so an applied paint can hold up there for longer periods.

Therefore, pressure-treated wood has a lower ability to soak up the liquid.

Where can I use pressure-treated lumber?

The best use of pressure-treated woods is to use them for outside applications like building a wooden structure of a house, office, using them on the rooftops, or even making patio furniture.

For some good reasons- the ability to resist moisture is great since outside furniture is less caring than indoors, with the use of such wood making them self-sufficient to prevent insects from eating them and making them weaker.

Is treated wood as strong as regular wood?

In a word- NO. The pressure-treated woods are not better than regular woods in terms of strength.

It’s for the fact that pressure-treated woods don’t absorb water due to chemicals that prevents moisturizer as well.

It makes them more prone to get cracked. Unlike regular woods which absorb some amount of water for years that increase their density level, increasing their overall strength.

However, in terms of durability, the pressure-treated woods deserve a plus point only because of the chemicals which make them anti-pest.

What’s bad about pressure-treated wood?

Although pressure-treated woods are popular, add a lot of benefits to regular woods. However, there is something bad about them as well.

Chemical risks.

Since pressure-treated lumber is full of chemicals, it can be toxic for humans in cases of burning them, using them to cook a meal, even cutting them they release a lot of chemicals which can be hazardous to humans.


Compared to regular woods these are costly because of the treatment they undergo. Such as chemicals they cost a lot of money including the usages of machines like a vacuum, insection, and expertise puts extra money on them.

To work, safety wearables are required.

Unlike regular woods, you can’t just start off to work with such woods. The obvious reason is for sure hazards chemicals they have which spread through space instantly.

Always wear a mask, safety gloves, and make sure the room or grade is well ventilated.

Types of pressure-treated wood brands

There are several different sizes and kinds of treated lumber available. 

Selecting the right material for your project requires understanding the different types of material which can save you time and money in the long run.

Pressure-treated wood is manufactured by several different brands for various reasons. There are several types of pressure-treated wood, including fire retardants, pest-resistant, anti-rotting, and those that have more than one characteristic.

PYRO-GUARD® Products

Pyro-Guard a well-established wood company manufactures quality fire-retardant types of treated-woods products to use in a variety of projects.

Exterior Fire-X™ (XFX) Lumber & Plywood

In addition to fire-retardant wood and plywood, Exterior Fire-XTM (XFX) is often used for exterior fire protection projects where surfaces will be exposed to high temperatures. Moreover, this lumber is durable in humid environments and is the best choice for outdoor applications.

Exterior Fire-X™ BLUE Lumber & Plywood

Exterior Fire-XTM BLUE has the same fire-resistance qualities as Exterior Fire-XTM but is colored blue for easy identification. 

Unlike Exterior Fire-X (XFM) it’s lightweight and mainly used for indoor applications. 

Micro-Guard™ Lumber & Plywood

The plywood and lumber in Micro-GuardTM are treated with a corrosion and termite-resistant, fungal decay-resistant treatment. It’s one of the best types of pressure-treated wood if your project requires something that can protect against corrosion and other rotting things.

Moisture problems such as warping and twisting in plywood, or buckling or crowning in plywood projects installed in the future can be prevented by KDAT.

Copper Azole (CA) Treated Lumber

Copper-based preservatives are used in the treatment of Copper Azole (CA) Treated Lumber to prevent decay, rot, and termites.

CCA Rot & Decay Resistant-Treated Plywood

Since the mid-1930s, chromed copper arsenate (CCA) has been used as a wood preservative, granting plywood an instantly recognizable greenish tint. 

Chemicals used in pressure-treated wood.

In recent months, the U.S. Environmental Protection Agency has registered several new active ingredients for wood preservatives. 

Comparing these wood preservatives to older ones, they have lower levels of toxicity since they are being used in almost every pressured-treated wood. 

The EPA will re-evaluate these newer wood preservatives as required by FIFRA section 3(g).

According to the U.S. Forest Service, the followings are the chemical preservatives that are registered for use in residential lumber and timber markets. 


Aqueous copper quaternary (ACQ) is a wood chemical, the most popular and widely used protection chemical in many types of woods that prevent decay from fungus and insects.

In comparison with other chemicals, it shows very little toxicity, and it is more affordable than other alternatives. Therefore pressured woods containing these chemicals are good to use for indoor applications.

The ACQ application is registered for use on lumber, timbers, landscape ties, fence posts, poles, and other wood structures, pilings, freshwater and marine barriers, sea walls, decking, wood shingles, and other wood products.


Wood lumber can be protected with this chemical from humidity effects, such as protection from rainy weather. This wood is commonly used to make pressure-treated timbers used for outdoor uses.

For over 70 years, wood preservatives containing borate have been used to preserve interior wood, including joists, sheathing, sill plates, and many others.

Copper Azole

The materials used in copper azole treatment are greenish-brown in color, and they have little or no odor. 

It functions as a fungicide and insecticide, as well as a wood preservative. Copper azole is a water-based wood preservative. One of the widely used chemicals in Canada as well in the US.

Copper azole is used in many applications, including above and below ground, as well as freshwater and marine decking. It has water-repellent properties that allow the wood to stay afloat longer by preventing it from absorbing moisture.

Copper Naphthenate

Another widely used water-based preservative is used to make pressure-treated woods to protect against fungi and insects. It’s a byproduct of copper and naphthenate. Due to this it acts as anti-pest as well as leaving an attractive dark color on applied wood.

The copper naphthenate was first patented in 1951 and is primarily used in the treatment of wood that comes in contact with soil, water, and above ground, such as utility poles, docks, ports, piers, fences, and landscape timbers. 

Hardwoods, mainly, can be effectively protected against insect damage with copper naphthenate.

Copper- HDO (Bis-(N Cyclohexyl Diazonium Dioxy- copper))

Despite the copper’s ability to resist decay and inhibit fungi and bacteria growth, it isn’t as popular as ACQ or borates due to its lower efficacy. 

This ingredient is typically used in termite repellents and marine borers, both of which are protected by the arsenic in the wood preservative since it is a strong insecticide.

Polymeric Betaine

Polymeric betaine was first registered as an active wood ingredient in the United States in 2006.  DDAC (didecyl dimethyl ammonium chloride) breaks down to boric acid when it is applied to wood and acts as a strong anti-infest layer.

Pressure-treated woods contain these chemicals mostly used for indoor furniture, or wood materials which are protected from weather effects since it’s not a good resistant to water.

Consequently, hardwood pressure-treated woods are widely used due to their self-reliant nature in rough weather.

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