United States Department of Agriculture
Posts of ohia and robusta, pressure- treated with two preservatives--chromated copper arsenate and pentachlorophenol, are being tested for durability at the Makiki Exposure Site, Honolulu, Hawaii. All treated posts are still sound after 5 years. Untreated ohia posts averaged 4 years of service life before failing; untreated robusta posts averaged 4 ½ years....
Round posts of 10 Hawaii-grown wood species were treated with copper chromate-copper arsenate by the double-diffusion process. These and untreated posts were exposed for 10 years. Except with two coniferous species, the treatment did not lengthen service life enough to be judged worthwhile.
Exposure of double-diffusion treated and untreated round posts of Hawaii-grown wood showed that (a) untreated 3- to 5-inch posts of 10 species will last from less than a year to 3 years, depending on species, and that (b) except for three species, the treatment did not afford a service life long enough to justify using it.