30/40 Trapezoid Diamond Grinding Segments
Trapezoid segment, 30/40
The coarse metal bond that opens the slab
A 30/40 trapezoid segment is a coarse, metal-bond diamond shoe fitted to a floor grinder. It removes the weak surface layer of the concrete and cuts an open profile, which is what a resin primer grips. It is the first grind on a slab before any epoxy flooring is laid.
Everything on this page after it depends on this one being done properly. Resin does not stick to concrete; it sticks to the profile you leave in concrete. The 30/40 metal bond is what cuts that profile.
Three passes, each at ninety degrees to the last, before a single pail is opened. Nine shoes on the head, two segments a shoe.
Why not acid
Acid etching is the alternative, and it is the reason we get called out to strip floors. It takes an hour instead of a day, costs almost nothing, and leaves a surface that looks right and holds nothing. The coating comes away in sheets, usually in the second year, usually in one piece you can lift with your hands.
If a quote is materially cheaper than ours, this is almost always the line it is cheaper by.
What it leaves
An open, uniformly scratched plane with the laitance gone and the aggregate just showing. That is what the primer keys into, and it is the difference between a floor bonded to your slab and a floor lying on top of it.
Without itAn acid etch instead: an hour of work instead of a day, and a floor that comes off in sheets inside two years.
What to ask
Ask to see the slab after the grind and before the primer. It is the one stage a contractor cannot fake, and the one you will never be shown unless you ask.
Where it is used
Day 01 of the job, prep, on every system we lay: decorative epoxy, flake floors, urethane cement, quartz broadcast, heavy industrial and repairs & recoats.
Questions people ask
What does 30/40 grit mean on a diamond grinding segment?
It is the size of the diamond, and a low number is coarse. A 30/40 segment cuts aggressively, removing laitance, curing compound, thin coatings and small high spots. Finer grits can follow it, but a slab going under resin is not polished: it is left open enough for the primer to key in.
Is diamond grinding better than acid etching before epoxy?
For a floor meant to last, yes. Acid etching is quicker and cheaper, but it leaves a shallow, uneven profile and a residue that has to be neutralised. Diamond grinding removes the weak top layer mechanically and leaves a consistent profile, which is why resin flooring manufacturers call for mechanical preparation.
How can I tell if my slab was ground properly before coating?
Look before the primer goes on. A properly ground slab is evenly dull and scratched all over, with no shiny patches of the original surface, no paint left on it and the fine aggregate just showing. Once the primer is down, the preparation can no longer be seen.