Pressure Treated Plywood: Your Go-To Guide for All You Need to Know

You have probably seen or heard of pressure treated plywood when choosing your lumber, but do you know what that really means? Which type of treated lumber is the best for different uses? This article will be your go-to guide on all things pressure treated plywood. Leaving the guessing out of finding out what kind of lumber you need.

Pressure treated plywood is plywood that has undergone a special pressurized process that increases the wood’s durability and makes it less prone to rot, water damage, mold, or insect damage. It basically gives the wood a higher density, making it harder for any of those things to infiltrate.

Pressure treated plywood, like the name states, uses pressure to push chemicals into the wood. So, the pressure itself is not making changes to the wood but is evenly distributing the chemical into the plywood. This process allows for control over how the chemical is being used and the even distribution makes for a better quality and stronger material.

Short answer is no, pressure treated plywood and heat treated plywood do not describe the same product. But these two types of treatment do have some crossover.

Heat treated plywood is wood that is placed in a kiln and is exposed to high heat until the internal temperature of the wood reaches 133 degrees for thirty consecutive minutes. This should not be confused with kiln drying. Kiln drying uses lower temperatures for a longer period until the moisture level is under nineteen percent. Kiln drying is a longer process that is specifically used to lower moisture levels in wood without warping or bending. These two are similar in the way that they both make use of a kiln, but they are unique in what they do to the wood.

Heat treatment is used as a sterilization process and does not change the wood’s density or other characteristics the way that kiln drying does. Heat treatment ensures compliance with the ISPM 15 regulations that state wood must be sanitized before import or export.

This process kills off insects and other pathogens that might be contained in the wood. The Pinewood Nematode and the Asian Longhorned Beetle are the most commonly found insects in wood pallets. This process helps to eliminate them and keep wood products healthy.  ISPM 15 requires all hardwood and softwood to be treated. The wood will garnish a stamp that states that it has met all requirements. This is crucial if you need export lumber. So far, 130 countries have adopted this standard, including the United States.

As you can see, pressure treated plywood and heat treated plywood are different things entirely. But pressure treated plywood has most likely gone through a heat treatment before it continues its own unique process.

Pressure treated plywood is usually reserved for wood that may come in to contact with excessive moisture. This wood can be used residentially for external wood such as, decking, fences, docks, or any other wood that would have prolonged exposure to water.

It can also be used in other industries as well. Construction industries will use pressure treated plywood in bridges, guardrails, or any other projects that need to be outdoors and withstand the elements.

There is a difference between wood that is above the ground and what touches the ground, or ground contact wood. Wood that will have ground contact will have to go through a longer process, so that it has twice the level of chemical retention compared to non-ground contact wood.

1.  Borate:  Borates are composed of sodium salts than is then used in a water-based solution. This chemical helps to keep the color of the wood and protect against mold, insects, and general breakdown. Since it is mixed with a water-based solution, it can start to leak out in rainy or wet areas. Best for dry locations.

2.  Alkaline Copper Quaternary (ACQ):  This is one of the most environmentally friendly options of the types of pressure treated plywood. It is made with soluble copper and quaternary ammonium alkyl. Protects against mold, insects, and general breakdown. It does change the color of the wood to a darker brown tone. There is no arsenic or chromium contained in this preservative.

3.  Noncombustible Wood:  This is wood that has been treated with a fire-retardant chemical before being pressurized. This is to help with flammability but does not completely take away risk. Can be used residentially or commercially, but not advised to be painted because it may affect the way it performs.

As stated above, the pressure treated plywood process uses pressure to push chemicals into the wood in an even and controlled amount. The wood will go into a special cylinder chamber, called a retort, where it will begin its treatment.

Once in the chamber, the machine will seal and depressurize to get as much air out as possible from the wood’s cells. Then the chamber will flood with chemicals and pressure will be applied for a determined amount of time.

The different pressure treated plywood is put into separate categories based on what it is going to be used for. What it is used for will determine its “retention level,” or the amount of chemicals that are retained after the treatment process. If it needs a higher retention level, it will be left in the chamber for a longer period.

Once the pressure treated plywood is finished, it will be placed somewhere to completely dry before being delivered. This can be a lengthy process, but it makes for a much stronger wood.

Yes, you heard right. Pressure treated plywood was made with arsenic at one point. It’s hard to imagine who approved that for residential use! But don’t worry today’s pressure treated plywood is completely safe.

Before 2004, pressure treated plywood was being made with something called Chromated Copper Arsenate (CCA) that helped to prevent the wood from rotting. CCA contains arsenic, chromium, and copper and was used in the United States starting in the 1970s.

The Environmental Protection Agency phased it out in 2003 because of the dangers that the chemicals presented and the rising public concern of arsenic-contamination in children’s playgrounds. The EPA worked with the wood manufacturers to remove wood with CCA from any residential use. It can still be used in other commercial products that humans will have little contact with it.

They have since kept a close eye on all the remaining ways to pressurize wood. This is another reason why it is important to only buy wood that has a regulated stamp of approval.

For specialized wood, you need specialized fasteners! In the pressure treated plywood that is made with Alkaline Copper Quaternary, you must have special fasteners because of the chemical reaction that can take place between the fastener and the wood.  The ACQ will start to corrode regular fasteners and the water that ACQ attracts accelerates the process.

Any fastener used must be rate for ACQ use, which will be labeled on packaging. The wood treatment industry recommends hot-dipped galvanized or stainless-steel nails to be used with this type of pressure treated plywood.

Conner Industries is a leading provider of industrial wood and packaging solutions. Specializing in cut lumber needed for pallets, crates, skid parts, fully assembled custom pallets, integrated packaging solutions, and other services that can be tailored to each individual customer.

With 14 different locations, we have the ability to meet the needs of our customers quickly and efficiently nationwide. Reach out to one of our knowledgeable team members today to learn how we can help your business!