Preservative Penetration Variations in Hickory

Nine mockernut hickory trees (Carya tomentosa Nutt.) at least 13 inches d.b.h., with specific gravities from 0.67 to 0.75 and growth rates of 15 to 24 rings per inch, were felled. From these trees 80 usable sticks, 4 by 4 by 48 inches, were sawn so as to include the maximum amount of sapwood possible. The sticks were vapor-dried and treated with creosote-petroleum by the Rueping process. After a 5-month storage period they were cut transversely to produce 1-inch-thick wafers. Microscope slides of material exhibiting penetration skips (hiatuses), birdpeck, and pecan carpenter worm stain were prepared. Percent of sapwood penetration and penetration patterns were recorded. Average retention was 9.3 lbs. preservative per cu.ft. Only 46 percent of the sticks had commercially acceptable penetration, 85 percent of the sticks exhibited penetration skips. Hiatuses originally present were not reduced by diffusion over a 5-year period. The majority of hiatuses were caused by “mineral streak” stains (a result of sapsucker attack) and stains from pecan carpenter worm galleries. Stained areas which obstructed penetration had heavy extractive deposits within longitudinal parenchyma, ray cells, vessels, and (to some degree) fiber tracheids. Some penetration skips were not attributable to stains and appeared to be associated with unpenetrated longitudinal parenchyma. Since hickory trees are susceptible to sapsucker and grub-hold damage, presence of stain is important whenever hickory is treated by impregnation.

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