Durability of heartwood in treated southern pine bulkheads

Many premature failures of southern pine timber bulkheads are attributable to marine borer attack on poorly penetrated heartwood. Incising with a very dense pattern and lengthening the pressure period improved chromated copper arsenate (CCA) penetration into the heartwood. Specimens of Virginia and loblolly/longleaf pine were treated with CCA to 1.5 or 2.5 pcf or with creosote to 25 pcf (nominal sapwood retentions), with or without pre-treatment incising, and were exposed to marine borers in Chesapeake Bay, Va., and in Key West Bight, Fla. Some unincised, CCA-treated Virginia pine specimens were destroyed by shipworms after only 34 months’ exposure in the Chesapeake Bay. Incising improved CCA penetration into Virginia pine enough to prevent shipworm attack for 34 months, but penetration was nevertheless poor, and premature borer damage appears likely. The CCA penetration of incised loblolly/longleaf heartwood specimens was nearly complete at 1/4 inch beneath the surface. At Key West, Limnoria were less able to attack poorly treated panels than were shipworms at Chesapeake Bay. Specimens treated with creosote were readily attacked by Limnoria tripunctata. Removal of 1/8 to 1/4 inch of wood with a jointer, after incising and CCA treatment, exposed small untreated areas through which shipworms and, to a lesser extent, Limnoria were able to burrow.

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