Watch the video on Pressure-Treated Wood Fasteners.
Pressure-treated wood is commonly used in the construction of patios, decks, and fences because it lasts longer than untreated wood. Until recently, arsenic was used as a preservative in the most common type of pressure-treated wood available, CCA (chromated copper arsenate). Because of the health risks associated with this chemical, the EPA banned the use of CCA lumber in home construction in January 2004.
ACQ (alkaline copper quat) lumber is one of the varieties that replaced CCA lumber. ACQ uses copper instead of the harmful arsenic, making it environmentally safer. Unfortunately, when the copper in the wood makes contact with metal, such as common aluminum building nails, a chemical process called "galvanic corrosion" occurs.
Galvanic corrosion is a process where one metal, in this case the copper in ACQ, steals the integrity or strength of another metal it is in contact with, like the aluminum nails or fasteners. In a relatively short period of time, sometimes less than a year, these nails can be completely corroded, causing structural instability to the home and creating possible safety hazards.
The best practice when working with ACQ lumber is to use G185 coated or stainless steel fasteners.
The term G185 refers to the way nails or fasteners are treated. G185 means the fastener has been galvanized (hot dipped) with 1.85 ounces of zinc per square foot of surface area. Zinc doesn't interact with the copper in ACQ pressure-treated wood the same way aluminum does, so your porch, sill plate, or fence won't be compromised.
Here are a few tips on using the appropriate fasteners on pressure-treated wood:
- G185 fasteners (nails and straps) can be used just like aluminum nails.
- Stainless steel fasteners work as well as the G185 type.
- G185 fasteners are very common today, and only slightly more expensive than standard aluminum or steel fasteners.
For more information on pressure-treated wood and the switch from CCA to ACQ, check out the EPA's Regulating Pesticides
section of their website, or click here for information about restrictions on arsenic use.
Under pressure
Ever wonder how they make pressure-treated wood or why it's so darn heavy?
Almost 90 years ago Dr. Karl Heinrich Wolman invented the process where raw lumber is placed in a vacuum sealed tank with a cocktail of preserving chemicals. The tank then is pressurized and the chemicals are forced into the wood. Once the tank is drained, the process is complete and the lumber is sent to market.
The amount of pressure and length of time the lumber is treated will determine the amount of chemical preservative forced into the wood. Pressure-treated wood is classified by the "retention" or number of pounds of preservative per cubic foot of wood. Wood with a .25 (1/4-pound of preservative per cubic foot) rating can be used for decking, fencing, and most exterior construction, while pressure-treated wood with a 2.5 rating is used for salt-water dock construction.
Use care when cutting or disposing of pressure-treated wood. Never burn pressure-treated wood -- especially CCA. Arsenic won't break down when burned, so the ash is even more toxic than the lumber.
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