An additional benefit of being solvent free is that they do not attack the underlying primer. Epoxies must be mixed in the proper ratio. Too little curing agent will weaken the filler and cause it to crumble later on. Epoxy fillers are preferred over polyester fillers below the waterline because polyester fillers have a greater propensity to absorb water. Epoxy fillers designed for below the waterline use will last much longer.
Conventional fillers are usually single part products and are easy to use.
This type of filler should only be used with one-part primers. They are designed to be applied in thin layers to allow the film to completely harden. Seam Compounds Seam compounds are used at joints on wooden planked hulls as well as keel joints to prevent water from penetrating. Epoxy Surfacing and Fairing Compound can be used above the waterline to the surface prior to applying topside finishes. Epoxy Surfacing and Fairing Compound can be used to fill pinholes between coats of two-part polyurethanes, due to its ability to trowel to a very line, smooth finish.