Do you want your wood building project to last?
Mike Brugger
  

Do You want your wood building project to last? 
Now that the holidays are over, you may start thinking about building projects for next summer. Whether it is a barn, a deck or an outside item, many of these projects will include pressure preservative treated wood. Pressure preservative treatment is used to reduce decay, rot and termite attack. Using the wood treated with the right chemicals at the correct levels and using the right fasteners will greatly improve the useful life.

CCA or ACQ Perservative
For many years wood treated with Chromated Copper Arsenic (CCA) was widely used in commercial and residential construction. Now the use of CCA treated wood has been restricted to a few mahor structural applications, including posts for post frame buildings.

A common new preservative is a combination of copper and quaternary ammonium compound (quat) dissolved in an alkaline carrier system. It is often referred to as ACQ. Copper is the primary ingredient. Gone are the chromium and arsenic, which are being replaced by a solution of ammonia. ACQ-treated lumber looks very  much the same as CCA-treated wood, with perhaps a slightly browner color. Some manufacturers also offer ACQ treated wood with a water repellent that is pressure treated into the wood.

Since copper is expensive and wood has different exposures to the environment, different levels of treatment are used. The level of treatment is expressed in pounds of active material retained in a cubic foot of wood.

Application - Retention (pounds per cubic foot) - Uses:

• Above Ground - 0.25 - Decking, fence boards, hand rails, deck supports

• Ground Contact Fresh Water - 0.40 - Fence posts, landscaping, piers, docks, etc.

• Permanent Wood Foundations - 0.60 - Wood foundations, crawl spaces

• Poles - 0.60 - Building, transmission and distribution poles

Purchase wood with at least the minimum retention level for the intended use. Using material with a higher content will increase the cost and can provide some additional protection. While using material with a higher content will increase the cost and can provide some additional protection. While using material with lower retention will reduce the protection, which leads to a reduced useful life. Treated wood should have a treatment stamp or tag stating the level of retention and, usually, the application. An would be "Ground Contact ACQ 0.40."

Other treatment materials include copper-azole and borate. As with ACQ-treated wood, select the wood with the proper level of treatment for the application.

Most treated wood has not been dried after treatment. During drying, wet wood will usually shrink causing cracks between boards. Using wood that has been re-dried after treating will greatly minimize the cracks.

Fasteners for treated wood
Wood preservatives can be hard on fasteners and fittings. A wrong fastener can cause very early failure. Contact with the flashing of the wrong material can cause premature failure. Carbon steel and aluminum fasteners and fittings should not be used with ACQ-treated wood. Fastener and hardware manufacturers have suggested the minimum hot-dip galvanized requirements should conform to ASTM Standards ASTM-A153 (Hot-Dip fastener products) and ASTM-A653 (Coating Designation G-185 for Hot-Dip connector and sheet products). Stainless steel fasteners and connectors are required for permanent wood foundations below grade and are recommended for use with treated wood in other severe exterior applications such as swimming pools, salt water exposure, ect. - Type 304 and 316 are the recommended grades to use. Follow the manufacturer's specific recommendations for acceptable fasteners.

Aluminum should not be used in direct contact with ACQ-treated wood. Spacer materials or other physical barriers are recommended to prevent direct contact of treated wood and aluminum products. A 1/4 inch minimum spacing must be allowed for between the treated wood and the aluminum products.

Another option is to use a polyethylene barrier, with a minimum thickness of 10 mils, between the treated wood and the aluminum product.

Nine safety tips
The following are some recommendations for safe use of preservative treated wood:

• Do not burn preserved wood.

• Wear a dust mask and goggles when cutting or sanding wood.

• Wear gloves when working with wood.

• Some preservative  may migrate from the treated wood into soil/water or may dislodge from the treated wood surface upon contact with skin. Wash exposed skin areas thoroughly.

• All sawdust and construction debris should be cleaned up and disposed of after construction.

• Wash work clothes separately from other household clothing before reuse.

• Preserved wood should not be used where it may come into direct or indirect contact with drinking water, except for used involving incidental contact such as fresh water docks and bridges.

• Do not use preserved wood under circumstances where the preservative may become a component of food, animal feed or beehives.

• Do not use preserved wood as mulch.

Mike Brugger, associate professor, can be reached at 330-263-3636 or brugger.1@osu.edu