TotalBoat FixWood epoxy putty cures to a waterproof material, but discretion should be as to whether it is the right product for an underwater repair. As an epoxy material, FixWood is waterproof and will remain stable when exposed to water, but it should never be used as a substitute for underwater seam compounds, or underwater caulking for wooden hulls. The main risk that may occur when using FixWood below the waterline on wooden substrates is that natural expansion and contraction of soaked, swelling wood may lead to delamination.