Iron Stain from Metal Fastenings May Accelerate Decay in Some Woods

In a study on the effect of iron stain on rate of decay in various woods, heartwood blocks 2 by 2-1/2 by 3/4-inch were cut from 2-inch strips of true mahogany (Swietenia sp.), white oak (Quercus alba), yellow-poplar (Liriodendron tulipifera), redwood (Sequoia sempervirens), and Sitka spruce (Picea sitchensis). The test blocks were dipped in hot water for 10 seconds and placed in the jar between layers of wire nails. The jars with the blocks and nails were sterilized by steaming at atmospheric pressure for 45 minutes and held for 1 month in a room maintained at 97 percent relative humidity and 80?F. Control blocks were placed in jars without nails. Following 1-month conditioning period, both the iron-stained and the control blocks were removed from the jars, conditioned to equilibrium moisture at 30 percent relative humidity and 80?F. and weighed. Fungus cultures of Lenizites trabea and Poria incrassata were prepared in Kille flasks containing 2.5 percent malt agar. The test blocks were sterilized by steaming at atmospheric pressure at 100?C. for 30 minutes, then were placed in each culture flask. Half of the blocks of each species were placed on cultures of each of the two test fungi and the cultures were incubated at room temperature for 4 months. Test results showed iron stain increased decay caused by both fungi in mahogany; by Poria incrassata in white oak; Lenzites trabea in yellow-poplar. The results with white oak and yellow-poplar suggest that different portions of the extractives may be differentially toxic to L. trabea and P. incrassata. Further study showed the radial position of the wood in the tree greatly affects its natural resistance to decay and that the iron stain can contribute to accelerated decay. The decay in the galvanized nail blocks averaged only three-fourths as much as in the controls. Study of the effect of iron on toxicity to fungi or hot-water extractives of mahogany showed that the hot-water extractives of mahogany were toxic to the fungi and that the addition of iron to the extractives markedly reduced their toxicity. Growth of Poria incrassata was retarded much more on the untreated extractive medium than was Lenzites trabea. In an additional test the addition of iron to the hot-water extractives of mahogany not only reduced their toxicity to both L. trabea and P. incrassata but also completely inactivated those portions of the extractives that are normally toxic to P. incrassata. At low relative humidities there was no difference in the moisture content of iron-treated and untreated wood. At high relative humidities of 90 to 97 percent, iron-treated wood of some species may have somewhat higher moisture content than untreated wood.

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