Mysterious Staining on Fresh Water Pontoon Boat Flooring

Staining on the fresh-water use pontoon boat flooring was thought by the marine surveyor who performed the initial inspection to be at the bond layer with the underlying plywood deck. He assured the owner-mother that she did not need to worry about endangering her barefoot child. Research had historically shown that most undesirable color changes in marine vinyl applications were associated with upholstery and due to chemical reactions associated with the urethane adhesive used to bond the outer vinyl to the foam. These reactions may cause discoloration, which reverses on exposure to the sun. However, in this situation, the sun was triggering the staining, and our investigation showed no urethanes in the flooring material. Therefore, we concluded that something else was happening.

Analysis of a cross section revealed that the stain actually originated at the exposed “wear” surface, not the bond line. By this time, boating season was over, so health concerns were put on hold while further testing was planned. FTIR revealed that all layers of the material were PVC. However, extraneous carbonyl peaks were found in the exposed layers with the darkest stain, indicating degradation. Additional SEM inspection of the wear surface revealed a maze of cracks that had not been visible with the optical microscope. EDS revealed that the stained area had higher sulfur. The writer noticed that the stain color matched that of her sulfur bacteria contaminated 98 foot deep well-water drenched shower curtain’s. Bacterial sources of the stain were unsuccessfully sought. After additional SEM work, the carcasses of algae were found. Research indicated that numerous species of photosynthesizing red algae inhabit the body of water favored by the pontoon boat owners. The insurance company and boat owners were satisfied with the extent of the investigation, and accepted the epistemologically grounded findings.