Can epoxy be applied over a concrete sealer?

Not directly, and this is one of the most common DIY mistakes we see. Existing sealers create a barrier that prevents epoxy from properly bonding to the concrete underneath, which leads to peeling and bubbling within months even if the initial application looks fine. The sealer has to be mechanically removed, typically through diamond grinding, before any new coating goes down. This is also a good opportunity to check for cracks or moisture issues that the old sealer may have been hiding. Skipping this step is one of the fastest ways to end up redoing a garage floor twice instead of once.

Have an old sealer or coating on your floor already? Our St. Louis epoxy flooring team can grind it down and start fresh the right way.

A simple water test is a good first check: if water beads up on the concrete instead of soaking in, there’s likely a sealer present. A professional can confirm this and grind it away before applying any new coating.