Water-based stains can be applied to a previous layer of cured epoxy, or to a substrate that is intended to be clear-coated with epoxy. The stain must be completely cured before adding the next layer of epoxy. It is also strongly recommended to test this on a small sample piece prior to executing this on an actual project. Make sure you do not use solvent-based stains, which have a much higher chance of acting as a contaminant to the epoxy, or causing delamination.