Is It Okay to Put Another Coat of Epoxy Over a Coat of Cured Epoxy?
This is perfectly acceptable, as a chemical bond is not possible once the epoxy has cured. Therefore, a “mechanical” bond is required, which means the cured epoxy should be sanded lightly before you apply the next coat. The first coat needs to have a surface that is almost white. It’s a good idea to use 80- to 120-grit sandpaper; do not use finer paper.
If a blush or bloom has developed on the first coat, it is crucial that you remove it. With most epoxies, it is possible to remove the blush or bloom by washing the epoxy with warm water that has a little bit of dishwashing liquid in it. Another fast way of removing it is through the use of a trisodium phosphate solution.