The chemical used to preserve Wolmanized® Heavy Duty™ pressure-treated wood is a mixture of the oxides of copper, chromium, and arsenate known as CCA. The preservative has been formulated to render wood useless as a food substance for termites and fungi while keeping the wood attractive, clean, odorless, non-staining, and safe to handle when used as recommended.
Unlike the commercially produced trivalent arsenic, the arsenate in Wolman® CCA is in the form of inorganic pentavalent arsenate—a naturally occurring trace element. In the treatment process, the pentavalent arsenate becomes fixed, or chemically bound, in the wood cells as highly leach-resistant insoluble precipitates.
About Fixation
The reaction of chromated copper arsenate with the wood substrate is termed "fixation" because the preservative compounds are fixed in the treated wood in a highly insoluble state. However, some chemical may migrate from treated wood into surrounding soil over time and may also be dislodged from the wood surface upon contact with the skin. Fixation accounts for the permanency of the preservative in the treated wood, which in turn, explains the leach resistance and durability of the product.
The fixation mechanism is complex and the reactions involved are primarily dependent upon wood species, preservative formulation, concentration, and temperature. The result, however, is that the preservative becomes leach-resistant precipitates.
Retention & Penetration
Wolmanized Heavy Duty pressure-treated wood is treated to various retention levels that are intended to protect the wood for particular applications. Retention levels indicate the amount of preservative retained in the wood in a specific assay zone. In North America, retention is expressed in pounds per cubic foot (pcf).
Retention levels or treating quality procedures are marked on Wolmanized® wood. The accompanying table outlines CCA retention levels required by the American Wood Protection Association for various applications.
Retention varies with depth in the wood, so preservative penetration also affects wood longevity. In species with large amounts of sapwood, such as southern and red pine, the preservative must penetrate 2.5 inches or 85% of the sapwood to meet standards. In western species that are predominantly heartwood, the wood is incised to ensure a treated shell, and any cut surfaces should be field-treated in accordance with AWPA standard M4 with a preservative containing at least 2% copper.
Retention Requirements Of The American Wood Protection Association1
| Application | Use Category | CCA (pcf) |
| Lumber, Timbers and Plywood | ||
| – Above Ground | 1, 2, 3A, 3B | 0.25 |
| – Ground / Fresh Water Contact | 4A | 0.40 |
| - Salt Water Splash | 4B | 0.60 |
| - Wood Foundation | 4B | 0.60 |
| - Salt Water Immersion | 5B | 2.50 |
| Piling and Columns | ||
| - Structural Poles | 4B | 0.60 |
| - Foundation / Fresh Water | 4C | 0.80 |
| - Salt Water Immersion | 5B | 2.502 |
¹ Wolman CCA preservative meets or exceeds AWPA P5 and Federal Standard TT-W-550. The treating process and the above results meet or exceed Federal Specification TT-W-571 and AWPA Commodity Standards as applicable.
² For round piling used in the northern zone (New Jersey and north on the East Coast, north of San Francisco Bay on the West Coast), a retention of 1.50 pcf is acceptable (UC5A).
