Pressure Treated Lumber (pressurelumber)

Pressure Treated Lumber

by Don Janssen, UNL Extension Educator

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By now, the pressure treated lumber you will find in stores has been treated with one of the new, more "environmentally friendly" pressure treatment chemicals. The former, long-used treatment known most commonly as CCA has been out of use for over two year, so stocks of lumber using that treatment process should be gone.

Today's pressure treating chemicals rely on copper in new formulations to stabilize it in ground contact and wet conditions. You will see codes such as ACQ-C, ACQ-D, and ACQ-D Carbonate on some lumbers. These are all versions of Alkaline Copper Quaternary. Other pieces of lumber will bear codes like CBA-A or CA-B which indicate they were treated with a Copper Azole-based material. Copper is the primary decay-preventing chemical in all of these treatments.

One of the big changes you will notice when you purchase these new pressure treated woods is in the price. The new lumber is going to cost you more since the new treatments cost more. Another change is in the grades. Pay careful attention to the specific application on the end tag. Some of the wood will bear the recommendation "Above Ground." Less chemical has been forced into this wood to save money. Be sure to use only wood labeled for ground contact as posts or retaining walls. The key for the consumer is to read the end tag on the lumber. Any lumber sanctioned by the American Wood- Preservers Association will bear their initials "AWPA" and have a fairly easy to understand tag.

The greatest change is in the hardware required to connect these new copper-based pressure treated lumbers. This new wood is much more corrosive to fasteners than CCA. Do not use nails, screws or connectors that are labeled "galvanized" as these will start to corrode in just weeks. At a minimum, use fasteners labeled "hot-dip galvanized." Your better choice is to use stainless steel screws and bolts, Type 304 or 316. Some screw manufacturers claim their zinc galvanized coatings, although not hot-dip, are usable on all pressure treated woods. Be sure to ask if they warrant their use before committing a major project to questionable fasteners. Lumber and time are far more expensive than purchasing the correct fasteners. Lastly, you cannot use aluminum flashing. It will start to corrode immediately. Look for copper, galvanized or membrane flashing.

Many of the fasteners and other products may require special ordering, but a long-lasting outdoor project is easily worth the planning required to get the right materials.