To prep a garage floor for epoxy, grind the slab in a three-step sequence: start with a 30/40 metal-bond diamond shoe to open the surface, move to a 60/80 grit to remove deep scratches, and finish with a 120/150 resin-bond or metal-bond pass to achieve a uniform profile. For a typical two-car garage (40 m2), budget half a day per grit with a 250-480 mm walk-behind grinder. If the slab has old paint or epoxy, begin with a PCD shoe to strip the coating first. The goal is a clean, evenly profiled surface with no trowel marks or laitance, not a polished floor.
If the old floor has flaking paint or glue residue, run a PCD shoe first. The WerkMaster PCD Tooling for Coating Removing (JOY-WM-PCD1R1) is designed for this. Do not try to grind through 2 mm of old epoxy with metal bond; it will load the diamonds and stall the machine.
| Pass | Grit | Goal |
|---|---|---|
| 1 | 30/40 metal bond | Open laitance, remove trowel marks |
| 2 | 60/80 metal bond | Remove 30/40 scratches |
| 3 | 120/150 | Uniform profile for epoxy adhesion |
Shoes like the Diamond Trapezoid Grinding Disc (JOY-TP-R3) or Double Rhombus Segment Diamond Trapezoid Grinding Disc (JOY-TP-RH2) work well for the first two passes on normal garage slab.
A: Yes. New slab has a weak laitance layer; grind it off or the coating will peel within a year. Wait at least 28 days for cure first.
A: Yes, most equipment rental houses stock 250-480 mm planetary grinders with dust extractors. Budget for two extra sets of shoes.
A: Dry with vacuum for epoxy prep. Wet grinding leaves a slurry film that must be thoroughly dried and can interfere with adhesion.
A: Epoxy tolerates minor variations, but high spots over 2 mm must be ground down or they will show through the coating.
Rental shops charge by the day for the grinder and extractor, and shoes are sold separately. Budget for at least two sets of shoes per grit so you never run out mid-pass. A two-car garage typically fits in a single rental day if you prep cracks and degrease oil spots the night before. Hiring a pro crew costs more per square meter but avoids the two most common DIY mistakes: skipping the coarse pass and failing to vacuum between grits, both of which lead to epoxy delamination within a year.
After the final grind, wait 24 hours before applying epoxy if humidity is high. Grinding opens the concrete pores, and trapped moisture will blush the coating. Run a dehumidifier in the garage overnight if you are in a damp coastal climate.
Do not forget the edges. The walk-behind grinder leaves roughly a 10 cm untreated band along walls and columns. Finish these with a hand grinder and a small cup wheel before the epoxy crew arrives.
A garage floor epoxy prep job is three grits and a plan. Strip coatings with PCD, open with 30/40, refine with 60/80, and finish at 120/150. Keep the machine moving, vacuum between passes, and you will have a surface that grips coating for a decade.
