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Grind to a CSP 3 profile for thin epoxy coatings up to 20 mils wet film, CSP 4 for self-leveling epoxy from 40 to 125 mils, and CSP 5 for heavy mortar or broadcast systems over 125 mils. Most jobs start with 30/40 grit metal-bond diamonds, then a 60 grit pass to knock down the sharpest peaks. Pull-off adhesion must read at least 200 PSI before coating, and the surface must be dry, clean and free of laitance. Under-profile epoxy debonds; over-profile epoxy traps air and looks uneven through the film.
Epoxy is 100 percent solids and relies on mechanical bite into the concrete, not on chemical reaction with the paste. A smooth troweled slab offers almost no tooth, so thin film coating peels in sheets within a year. Grinding opens the pores and creates a uniform peak-and-valley texture that the wet resin wicks into. The American Concrete Institute classifies that texture on the CSP 1 to CSP 5 scale, and epoxy manufacturers publish a target range on their technical data sheet. Ignoring that range is the single biggest cause of coating failure on interior floors. A profile that is too fine leaves no key; a profile that is too coarse traps air bubbles and leaves a mottled film. Both failures show up within the first heating cycle, usually six to twelve months after application.
A 10 to 20 mil epoxy or polyurethane coating sits on top of the surface and does not fill deep valleys. It needs CSP 2 to CSP 3: a fine grit etched look, visible but without ridges that telegraph through the film. Use a 60 to 80 grit metal-bond pass, or a 30/40 pass followed by 60 grit. If you leave CSP 4 peaks on a 15 mil coating, you will see every peak through the cured film and the floor will look mottled. Walk the floor with a strong light at low angle before coating: any glossy strip is a spot that was not opened enough.
Self-leveling epoxy from 40 to 125 mils flows into small valleys but cannot hide deep gouges. It wants CSP 3 to CSP 4, achieved with a 30/40 or 16/24 grit metal-bond grind. Heavy mortar beds and quartz broadcast systems over 125 mils want CSP 4 to CSP 5, because the thick film needs deep mechanical key to carry broadcast load and resist delamination under rolling traffic.
Work in sequence and never skip a grit stage that leaves deeper scratches than the next pass can remove:
Trapezoid tooling like the JOY-TP-R3 triple-round segment disc leaves a consistent CSP 3 to CSP 4 pattern on planetary machines, which is why most epoxy prep crews run it as the first metal-bond step. If you are working on a smaller walk-behind unit, two passes at slow speed deliver the same profile as one fast pass on a heavier machine, because the diamonds need time to fracture the paste rather than polish it.
Set machine weight so each segment carries about 15 to 25 PSI of contact pressure. Too little pressure and the machine skims the surface, leaving blotchy profile; too much and the segments load and glaze. Overlap each pass by one third of the disc width and keep travel speed at roughly 1 meter per minute. A slow, single pass beats two fast passes because the diamonds have time to chip the paste rather than polish it.
Run a pull-off adhesion test at three points per 100 m². The epoxy primer should bond at 200 to 400 PSI and the fracture should be cohesive in the concrete, not at the primer line. If you read below 150 PSI, you are still looking at laitance or over-grinded paste; grind again with a coarser grit and re-test before the crew starts rolling coating.
The mistakes that send epoxy crews back to regrind are predictable:
A correctly ground floor feels uniformly rough to the palm, has no trowel lines or glossy patches, and wipes off with a white cloth that stays clean. Match that texture to the manufacturer CSP range, run the pull-off test, apply primer within 24 hours, and the epoxy will bond the way the data sheet promises. If you are unsure which CSP the coating requires, call the manufacturer technical line before grinding, not after the first coat fails. For a wider tooling choice, browse the full diamond cup wheel lineup and the grinding category page before you set up for the next slab.
Written and reviewed by JOY TECH - an SGS & BV audited, CE/RoHS certified diamond tools manufacturer founded in 2004, exporting to 50+ countries.
Our factory and quality management system are audited by SGS and Bureau Veritas. Products meet CE/RoHS requirements and every piece is 100% inspected before packing.
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