Concrete Grinding Levels Explained: From Prep to a Mirror Shine

If you have ever stood on a polished concrete floor and wondered how a rough slab turned into something that mirrors the lights above, the answer is a sequence of concrete polishing passes called grinding levels. Each level uses a different grit and a different bond, and each one prepares the floor for the next. Knowing the concrete grinding levels matters because it controls three things you actually care about: how the floor looks, how long it lasts, and how much it costs.

This is a no-jargon guide written for property owners in Toronto and the Greater Toronto Area. We will walk through the CSP prep grades, the diamond grit progression, and the finish you can expect at each step.

Why concrete grinding levels exist in the first place

Concrete is not a single material. Every slab is a mix of cement paste, sand, and aggregate, and the surface you see is mostly the paste. To make a slab smoother, harder, or more reflective, you have to remove the soft top layer and expose the dense matrix underneath. That removal happens in stages because each stage uses a tool that can only do so much before it stops cutting and starts polishing.

Think of it like sanding wood. You start with 60-grit to take down the rough, then 120 to smooth, then 220 to refine. With concrete, the principle is the same, but the grit numbers go far higher and the tools are diamond-bonded discs spinning under a planetary head. Skip a step and you leave swirl marks that the next pass cannot remove.

CSP grades: how rough is rough enough

Before any decorative work begins, the slab usually needs surface preparation. The Concrete Surface Profile (CSP) scale runs from 1 to 9 and was published by the International Concrete Repair Institute. It tells you how rough the prepared surface is, which determines what kind of coating or finish will bond to it.

If you are putting an epoxy floor in your garage, the installer should be aiming for somewhere in the CSP 3 to 4 range. Too smooth and the epoxy will peel within a season. Too rough and you waste material trying to fill the profile. Getting this part right is where a lot of failed coatings begin.

Diamond grit progression: the mechanical part

Once the slab is prepped, the polishing sequence begins. The grinder is a planetary head with three or four diamond-bonded discs, riding on a counter-rotating plate. Discs come in two basic bond types and a wide range of grits.

• Metal-bond diamonds handle the heavy removal. The diamonds are held in a soft metal matrix that wears away as work progresses, exposing fresh diamond. Used at 30, 60, and 100 grit.
• Resin-bond diamonds handle the refinement. The diamonds sit in a softer resin that releases polishing dust slowly. Used at 100, 200, 400, 800, 1,500, and 3,000 grit.

A typical residential polish runs through six passes: 30, 60, 100, 200, 400, 800. Add a densifier between the 200 and 400 passes to chemically harden the concrete. For a high-gloss commercial floor, add 1,500. For a mirror finish, add 3,000. Each pass is wet or dry depending on the dust control plan and the building’s tolerance for slurry.

Finish levels: cream, salt and pepper, semi-gloss, mirror

The final look of a polished floor is set by where you stop in the diamond progression and how much aggregate you exposed during the early passes. Industry shorthand recognizes four practical finishes.

• Cream finish at roughly 100 grit. Almost no aggregate showing. Smooth and matte. Good for spaces where you want concrete texture without shine, like a gallery or a minimalist studio.
• Salt and pepper at 400 to 800 grit. Light aggregate exposure that gives the floor a uniform speckled tone. The most common residential polished concrete finish in the GTA.
• Semi-gloss at 800 to 1,500 grit. Sharper reflections without full mirror clarity. Standard for retail floors and busy office space because it reads as polished while hiding scuffs better than a true mirror.
• Mirror finish at 3,000 grit. Reflects overhead lights with the clarity of glass. Premium look, premium maintenance, and you will see every fingerprint and shoe scuff.

Worth knowing: the same 800-grit pass on two different slabs can produce two different looks. The age of the concrete, the trowel finish during the pour, and how aggressively the early grinds exposed aggregate all change the final appearance. This is why honest contractors will polish a small test patch before committing.

How to choose the right finish for your space

Match the finish level to how the space is used, not to a magazine photo. Here is a working framework we use with clients across Toronto, Mississauga, and Vaughan.

• Garages and basements: usually a coating job rather than a full polish. If you want polished concrete in a basement, salt and pepper at 800 grit gives a clean look without showing every speck of dust. See basement applications.
• Warehouses and industrial spaces: 400 to 800 grit. The concrete is hard enough to handle pallet jacks and the finish is reflective enough to bounce light from the ceiling, which cuts lighting costs. See industrial applications.
• Retail and showroom spaces: 1,500 grit, sometimes 3,000 if the brand calls for it. The reflection becomes a design feature. See showroom applications.
• Open-concept residential: 800 grit salt and pepper is the sweet spot. High enough gloss to feel finished, low enough to forgive normal wear.

What grinding levels do to cost and timeline

Cost is driven mostly by the slab’s starting condition and how many passes the contractor needs to make. A flat, sound slab in a 1,500-square-foot residential basement typically needs six passes plus a densifier and runs roughly $7 to $10 per square foot for a salt-and-pepper finish. The same room finished to 3,000 grit climbs to roughly $11 to $14 per square foot because of the added passes and time on the floor. (Prices vary with site access, slab condition, and edge work.)

Timeline scales the same way. A two-person crew can usually run six passes plus densifier on 1,500 square feet in two days. A mirror finish adds roughly half a day. Curing of the densifier needs at least 24 hours before any traffic returns, regardless of grit level.

If your floor needs concrete resurfacing first because of cracks or pitting, add another day and another visit. Repairs are always done before grinding starts because patches that get ground in the middle of the polish sequence will not match the surrounding finish.

The four mistakes that ruin a polish job

1. Skipping a grit. Going straight from 100 to 400 leaves shadow scratches that the 400 cannot remove. The floor will look hazy in raking light no matter how many polishing passes follow.
2. Skipping the densifier. Without a lithium or sodium silicate densifier between the medium and fine passes, the concrete stays porous and the polish will not develop. The floor reads dull within months.
3. Polishing wet concrete. Slabs that have not cured for at least 28 days will not respond to diamonds the way mature concrete does. The result is uneven sheen and aggregate that sits below the polish line.
4. Wrong CSP profile for the coating. An epoxy applied over a CSP 1 surface peels because there is nothing for the resin to grip. An epoxy applied over CSP 8 is starved of material and looks pitted from day one. Both failures get blamed on the coating; both are prep failures.

Common questions about concrete grinding levels