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How Is Pressure Treated Lumber Made?

Wood is one of the most attractive building materials – Lightweight, durable, attractive, and easy to modify if needed.

One of the main downsides to using wood is that wood is prone to decay for a variety of reasons. Bacteria and fungus are attracted to wood, and will erode at it over time, especially in the presence of water. And many species of insects live in or even eat wood.

Any of these (or a combination of all of them) can reduce wood from useful building material to rotten garbage in as little as a year in certain extreme cases. And this applies in particular to wood used outdoors, where the elements and insects have full access to the wood.

The technique of pressure treating wood aims to solve this problem. Pressure treated wood receives a compound of certain chemicals to make it resistant to bacteria, fungi, and insects. As a result, this type of wood is able to last for far longer than untreated wood, even in conditions that would lead to the rapid decay of most types of lumber.

The process of pressure treating blasts the chemicals deep into the interior of the wood, meaning that the inside of the wood has just as much protection as the surface.

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What Chemicals are Used in Pressure Treated Wood?

The process of pressure treating wood is as follows: Lumber is placed into a vacuum sealed chamber or tank along with a water borne chemical preservative. The vacuum creates pressure that forces the chemical compound into the wood.

The chemicals used in pressure treated wood have changed slightly over the years, although there are some commonalities even as the formula has evolved.

CCA – Chromated Copper Arsenate

For years, the most popular formula for pressure treated wood was CCA. CCA uses compounds of chromium, copper, and arsenic.

The copper protects the wood against fungal growth, bacterial growth, and decay. The arsenic is toxic to wood-boring insects like termites, ants, marine borers, and other similar creatures. The chromium is a binding agent, helping the other chemicals stick within the wood.

Over time, concern grew over the use of arsenic (and to a lesser extent, chromium) in treated wood. Arsenic is regarded as a possible carcinogen, and is highly toxic to humans in large enough doses. And arsenic and chromium leaching out into soil and groundwater is a potential risk.

In 2003, the USA’s EPA banned the usage of CCA lumber in residential projects, and CCA has fallen out of favor. You can still find CCA treated lumber, although if you buy pressure treated wood it will likely not be CCA anymore.

ACQ – Alkaline Copper Quaternary

An alternative to CCA, ACQ is a far less toxic chemical compound due to the absence of arsenic and chromium.

Copper fulfills the same function as with CCA, making the wood resistant to decay, fungi, and bacteria. With ACQ, quaternary ammonium cation acts in the arsenic function, making the wood uninhabitable to insects.

Can You Pressure Treat Your Own Lumber?

It’s possible to treat your own lumber, although there are limits. You won’t have a pressure chamber or tank, meaning it won’t be possible to use pressure to force any chemical compounds deep beneath the surface of the wood.

That means any do-it-yourself treating technique is going to be more focused on making the exterior of the wood impenetrable, protecting the interior by keeping any bacteria, insects, fungi, or rot from getting there in the first place.

This means that any DIY treatment needs to be done with wood you know is pristine to begin with. If it’s already rotten or compromised inside, the treatment will be useless.

You can purchase any number of liquid treatment compounds, the best of which will be copper based. They have differing methods of application, so make sure to follow the steps indicated on whichever you pick out.

But be aware that no DIY treatment is going to approach the level of decay resistance that professionally pressure treated wood provides.

How Long Does Pressure Treated Wood Last?

pressure treated wood

Pressure treated wood will last at least a decade, but it can last for far longer than that. The key to extending the lifespan of pressure treated wood is combating moisture. If you water proof pressure treated wood, it can last for as long as 40 to 50 years.

Pressure treated wood’s chemical compounds mean that the wood won’t rot or decay, and won’t be ruined by insects. However, if you don’t take steps to prevent it the wood will absorb water over time.

The absorbing and drying process will cause the wood to swell and contract, leading to bends and cracks. Over a period of years, this will eventually destroy the wood.

If you apply water repellent treatment to the pressure treated wood, you’ll keep the wood from absorbing water. If you do so, this wood will last for decades without losing major structural integrity.

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