How to Identify Treated Lumber: A Comprehensive Guide

Your 130 2x2s from a 1960s pergola pose an interesting challenge. Considering the preservation of the wood and the potential for treatment, it's essential to understand the history of treated lumber and its identification. Here’s a detailed guide to help you determine if your lumber is treated.

Introduction to Treated Lumber

Treated lumber, which is designed to resist moisture and decay, became commercially available in the 1940s. However, it wasn't until the 1970s that it became a readily available product for general use. One of the popular brands, Wolmanized, gained prominence in the construction of decks and outdoor wood structures. This treatment was actually invented around 1911 and was stamped to warn consumers about possible arsenic content.

Key Characteristics of Treated Lumber

Identifying whether your lumber is treated requires a combination of visual inspection, odor assessment, and knowledge of specific markings. In the 1960s, the primary preservative used for exterior timber was creosote. If the wood was treated with this, it would have a strong creosote smell when cut, and the exterior would display a distinctive dark shade.

Inspecting the Wood for Treated Lumber

1. Look for a Yellow Interior: The interior of your 2x2s is yellow. This is an indication that the wood may have been stained or painted, but it doesn't necessarily mean it was treated. However, if the interior is green, it could indicate untreated timber that has decomposed due to moisture exposure.

2. Smell the Wood: Cut a small piece of the wood and smell it. If it has a chemical odor, especially a creosote smell, it is likely treated. Untreated wood generally does not have a strong smell.

3. Check for Stamps or Markings: Look for stamped markings on the wood, as treated lumber was required to be stamped to indicate the presence of arsenic. These stamps usually appear on the side of the wood or at the ends.

Historical Context of Treated Lumber

Before the 1960s, preservatives like creosote were used widely for exterior timber. Creosote-treated wood would have a distinctive dark exterior and a strong creosote smell. Over time, the wood may have darkened or greyed, but it would still be visibly different from untreated wood.

Copper sulfate, another preservative, was introduced in the late 1960s but typically came with an extra cost and was specified by the customer. After the 1970s, treated lumber became more common and was widely used for decks and outdoor structures.

Conclusion

Given the age and conditions of your 2x2s, they are likely treated lumber. Wolmanized and other treatments were introduced in the 1940s and became widely available in the 1970s. The yellow hue and potential presence of creosote or copper sulfate marks can provide clues to its treatment status.

For more detailed information, you can explore my Quora profile for additional insights. If you still have doubts, consulting a professional wood consultant might be beneficial.