Abstract:
Over-the-counter (OTC) wood preservatives can
provide wood with both a moisture barrier and fungicidal
protection against biodeterioration, yet there is little
comparative data on the performance of these
preservatives. In this study, the potential of various
low-toxicity, OTC preservatives was evaluated on five
western wood species, western redcedar (Thuja plicata),
western hemlock (Tsuga heterophylla), Douglas-fir
(Pseudosuga menziesii),lodgepole pine (Pinus contorta),
and coastal redwood (Sequoia sempervirens). The active
ingredients tested were copper-8-quinolinolate, copper
naphthenate, zinc naphthenate, 3-Iodo 2-propynylbutlycarbamate
(IPBC), Bis (tri-n-butyltin) oxide
(TBTO), TBTO\IPBC, TBTO\chlorothalonil, and TBTO\N
trichloromethylthio-phthalimide (Folpet). Small blocks
and stakes of each species were dipped for 3 minutes in
one of twelve OTC preservatives to simulate homeowner application. To examine the efficacy of these
preservatives, treated blocks were subjected to a
modified American Society of Testing and Materials
Standards (ASTM) D2017-81 soil-block test to evaluate
above ground decay resistance as measured by wood weight
loss following exposure to Postia placenta (Fr.) Cooke
or Trametes versicolor (L:Fr.) Pilat, a brown and white
rot fungus, respectively. Test stakes were placed in
soil-beds maintained in an environmentally controlled
greenhouse. The stakes were evaluated for the degree
of decay at 3 month intervals for the first year,
followed by 18 and 24 month ratings. Preservative
treatments improved performance of most species except
lodgepole pine; improvements were most noticeable in
soil-bed trials with redwood and western redcedar. The
results suggest that topical application of commercially
available preservatives has merit for enhancing the
performance of naturally durable woods in soil contact,
but their value for less durable woods is questionable.
Wood used above-ground will benefit most from such
topical treatments, however, for best performance a
yearly reapplication might be necessary for the less
durable wood species.
