Southern Exposure: Long-Term Field Testing of Wood Protectants

When researchers are looking to evaluate the performance of wood protectants, the harsher the environment the better. Which is why Forest Products Laboratory (FPL) researchers put specimens to the test in the Harrison Experimental Forest (HEF) in Saucier, Mississippi, and have been doing so for 80 years.

Generations of FPL researchers have used the HEF field site for sub-tropical field testing. Here Oscar Blew is rating posts at the HEF (1950’s).

Located about 35 miles north of the Gulf of Mexico, this sub-tropical field site receives about 60 inches of rainfall a year and has a mean temperature of 68 degrees Fahrenheit. The wood decay hazard in this area is rated “severe” according to the American Wood Protection Association Use Class Rating System and there is significant subterranean termite activity. When in ground contact, untreated wood rarely lasts 12 months in the HEF, to which researchers respond “challenge accepted.”

Long-term field testing of experimental and existing wood protectants involves installing samples (partially burying stakes or otherwise placing wood in contact with the ground) and, well, waiting. Researchers periodically return to the test site to unearth the samples and evaluate any deterioration that may have occurred.

In addition to ground contact tests, FPL researchers also test wood products in above-ground exposure, which evaluates other properties such as weathering, cupping, checking, and fastener corrosion in addition to fungal decay and termite attack.

The HEF has been the site of FPL field tests since 1938. The field stake shown below, installed in 1957, has been in ground contact for 60 years and shows no visible signs of decay or termite attack. The stake was treated with an early formulation of chromated copper arsenate (CCA) which is no longer used as a residential product but is still used on utility poles and marine pilings today.

Buried Treasure: This stake was treated with an early formulation of chromated copper arsenate (CCA) and installed in 1957. It has been in ground contact for 60 years with no visible signs of decay or termite attack.

Wood protection products and chemistries have seen a gradual shift over the decades from early wood preservatives (creosote, pentachlorophenol, and CCA) to more recent alternatives with fewer environmental concerns. Long-term field exposure tests yield critical data that is used to calculate the service life of wood products and ensure consumers get the best results by using the right product for the job.

Above ground decking made of thermally modified wood being evaluated to determine how it weathers in a severe climate.

In addition to wood preservatives, FPL is also conducting field testing of thermally modified and naturally durable woods in order to provide realistic exposure scenarios for a wider range of commercially available building materials and provide homeowners with independent evaluations of treated wood products.

The HEF is located on the DeSoto National Forest and is one of nineteen experimental forests operated by the USDA-FS Southern Research Station. This experimental forest was originally established in 1934 to provide long term silvacultural data on pine ecosystem management and later on the genetics of the native longleaf pines.

Blog post by Grant Kirker and Rebecca Wallace