Chromated Copper Arsenate (CCA) Pressure-Treated Wood

CCA Pressure-Treated Wood – A Lasting Choice

Seven Common User Questions:

Of all the wood products found in your local lumber yard, none has shown a more spectacular rise in popularity during the last 20 years than CCA pressure-treated wood. In 1976, it was a poorly understood material that was rarely, if ever, stocked by any Canadian yards; now it is unusual to find a dealer in North America who does not carry a generous assortment of decking, fencing and landscaping posts and timbers, much of it carrying a 40-year warranty against rot and insect attack.

Despite its increasing popularity, there are still many who are not totally familiar with CCA pressure-treated wood. Here are seven commonly asked questions posed by the “Do-It-Yourself” builder, with answers supplied by a well-known treater.

1. What exactly is pressure-treated wood?

As defined by CSA and American Standards, pressure-treated wood is a special product that has been placed in a sealed steel retort, flooded with preservative and subjected to a vacuum-pressure cycle of sufficient time to impregnate the wood cells to industry standards of established classes, retentions and penetrations of preservative. Usually, these pressure vessels are six feet or more in cross-section and 40 feet or more in length. They consist of industrial pumps, valves, electronics and gauges capable of maintaining a fluid pressure of 125 psi minimum, so as to force the preservative as deeply into the wood cells as possible.

All major nations of the world, including Canada, have issued standards governing penetration and retention of preservative relative to the end-use of the treated wood products. In Canada, we have standards prepared by CSA.

2. How many years will pressure-treated wood last?

This depends on how well the product is treated, including whether the wood is incised or not (incising is the punching of small holes in the wood by a special machine to assist penetration of preservative), and whether the wood is kiln-dried prior to treating. If the wood is treated to industry standards of retention and penetration, then available test and service records indicate that CCA-treated wood should last in excess of 40 years, even for marine or ground contact use. In all cases, properly CCA pressure-treated wood has been shown to outlast untreated cedar. Make sure you apply two coats of either a Copper or Zinc Naphthenate preservative to freshly cut ends of lumber, since complete penetration of preservative is seldom achieved.

3. Is CCA-treated wood safe to handle?

Yes, CCA-treated wood has been widely used throughout the world for the past 50 years. Extensive studies of acute and long-term toxicity effects, carried out by the public and private research institutions in North America and Europe, have demonstrated no special risks in the normal handling of CCA-treated wood by “Do It Yourself” builders and contractors. However, it should not be used in direct contact with stored foods, nor should any off cuts be burned since the gases formed when CCA breaks down add to the normal toxic load when wood is burned. As with any wood substance, a dust mask should be worn when sawing or working the product with power tools.

CCA is the abbreviation for Chromated Copper Arsenate. The chemical reaction that takes place inside the wood results in a stable, non-leachable product that is totally odour-free. The arsenate is in a molecular-bound state; quite different from elemental arsenic and far less toxic.

4. Is CCA-treated wood toxic to plants?

No. The product is defined as non-phytotoxic and cannot be translocated into the root, leaf or vascular system of a growing plant. It is commonly used in construction of nursery trays and greenhouses and is widely used in farm building construction, as well as fence posts, grape and tomato stakes, and mushroom trays.

5. Can CCA pressure-treated wood be painted or stained?

Yes. In fact, the chromated copper component of CCA has proven to act as an excellent primer. Tests carried out by the Forest Products in the U.S.A. show that wood products treated with chrome primer hold their paint or stain at least 50% longer than wood treated with normal primers. This means that the paint or stain you use to coat your CCA-treated wood will likely last at least six years before recoating. CCA-treated wood can also be glued with all commonly used adhesives.

6. How much more does CCA-treated wood cost?

In most cases, only about 25% more than the equivalent grade of lumber untreated – a small price to pay when the life expectancy is increased by at least three times that of the untreated wood.

7. How do I know if the product has been well treated?

A chemical analysis of the wood by a qualified technician is the only way to know for sure. When cross cutting treated wood, visible penetration of preservative often shows up as a greenish-grey zone, distinct from the whiter untreated zone.

If you have any doubts, contact the retailer or treater who can arrange for an inspection of the product. At least 1/4” of uniform penetration is required for adequate protection and a retention of 0.25 – 0.40 pcf of CCA.

In conclusion, it can be said that CCA pressure-treated wood is a clean, durable, versatile building material that is unlikely to be replaced by alternate materials and one which promises a lifetime of worry-free use for any of your outdoor projects.