I thought of using an epoxy finish on the garage floor of my new house when I moved in a year ago but a combination of paralysis by analysis and a delay getting in the house led me to use a concrete densifier/sealer because that's what the local contractor place had). The delay getting the keys meant I applied the product the day before we moved in and I didn't have time to burnish the floor to shine it up.
The current plan:
- Saturday - Pour undiluted Simple Green Concrete & Driveway Cleaner directly onto garage floor, let sit for 5-10 minutes, then scrub with this deck brush I bought, let it sit for 5-10 more minutes, then wash out of the garage and down the driveway with a garden hose.
- Sunday - If Saturday's plan didn't work (and I doubt it'll be enough), repeat the process but with my brother-in-law's pressure washer.
- Then - Use muriatic acid on any remaining trouble spots. I bought goggles and gloves for this step, but haven't bought the acid yet since I don't know if it's necessary.
- Eventually - Consider applying epoxy flooring depending on the collective recommendations of the good people at my local contractors.
Unless you're using a clear epoxy, you only really need to worry about surface dirts, oils, or any other paint or sealer impeding the bond between the concrete and the epoxy.
That includes fully rinsing the cleaning solution.
Getting the floor completely stain-free doesn't need to be the goal.
The acids are used more to abrade and etch the surface than to clean it. It roughs up the concrete slightly to allow the epoxy coating to grip into the concrete.
Depending on how smooth/rough/porous your concrete is, acid etching may or may not be necessary.