Evaluation of some polyurethanes as protective marine coatings for wood
J D Bultman, J E Pinto
Several polyurethane formulations were evaluated in the marine environment as possible replacements for Irish felt used on U.S. Navy minesweepers as a marine borer barrier between the main wooden hull and an outer, wooden sheathing which covers it. Pine panels coated with the candidate materials were tightly juxtaposed with untreated pine baitwood to simulate the hull/sheathing configuration, the baitwood serving as a substrate in which settling borer larve could metamorphose. Primarily, the purpose was to see if adult borers could perforate the coatings at the coating/wood interface and enter the wood beneath, however the ability of these coatings to survive in sea water for an extended time was also noted. Panels were exposed from 48 to 89 months in Panamanian waters. Teredinids were able to perforate four of the coatings from the baitwood; pholads were able to perforate all of the coatings with ease and were the major cause of coating damage at the coating/baitwood interface. None of the coating surfaces exposed directly to the sea water were damaged by teredinids or pholads, however the coatings on some of the panels were eventually reduced to tatters with large sections of the original specimen missing. This was a result of borer infestation of the underlying wood via prior pholad-induced holes which were uncovered when the panel faces were reversed in the panel/baitwood configuration during the exposure.