How to polish concrete

Metal-bond range

30–150 gritcutting steps

Resin-bond range

100–3000 gritrefining and gloss steps

Densifier point

after metal stepsvaries by system

Silica PEL

50 µg/m³8-hr TWA, 29 CFR 1926.1153

Grit skipping

one step maxskipped scratches show at gloss

Short version

• Two tooling families do two different jobs: metal-bond cuts, resin-bond refines.
• The densifier goes on partway through, not at the end, so the fine passes polish a hardened surface.
• Each grit has to erase the scratch pattern left by the one before it.
• Skipping more than one step leaves scratches that only become visible at high gloss.
• Silica dust control is a legal requirement, not a preference.

What is the grit sequence for polishing concrete?

The grit sequence runs from aggressive metal-bond cutting to fine resin-bond polishing, with the densifier applied between the two phases. The table below shows a typical progression; specific systems vary, and the tooling manufacturer’s sequence takes precedence over any general chart.

The first pass is the one that decides everything. How deep you cut in step 1 determines whether the finish shows only cement paste, a fine salt-and-pepper of sand, or full exposed stone — and once you have cut past the paste, you cannot go back.

Where you stop determines gloss. Ending around 400 grit gives a satin finish that hides traffic; going to 1500 or 3000 gives a mirror that shows every scuff. ASCC’s Concrete Polishing Council publishes the industry classification for both aggregate exposure and gloss level, and specifying a job in those terms avoids arguments about what “polished” was supposed to mean.

This page covers the mechanical process. For what the finished result looks like in a house, a garage, or a warehouse, what drives the price, and how to maintain it, see how to polish concrete floors.

What is the difference between metal-bond and resin-bond diamonds?

Metal-bond and resin-bond tooling differ in what holds the diamonds, and that changes what they do. Metal-bond segments carry industrial diamonds in a sintered metal matrix that wears slowly and cuts aggressively, so they remove material — coatings, adhesive, high spots, and the top layer of paste.

Resin-bond pads hold diamonds in a softer resin that wears faster and cuts more gently. They do not remove much material; they refine the scratch pattern until the surface reflects light. Running resin tooling on a floor that still has coating residue destroys the pads in minutes, which is why the metal phase has to finish completely first.

Hybrid or transitional tooling exists to bridge the gap. A transitional pad in the 50 to 100 grit range takes out metal-bond scratches faster than a resin pad can, which shortens the whole sequence on a hard floor.

Match tooling hardness to slab hardness, which is the opposite of what people expect. Soft concrete takes hard-bond tooling, because a soft bond would wear away before the diamonds do any work. Hard, densified, or power-troweled concrete takes soft-bond tooling so the matrix erodes and keeps exposing fresh diamond.

What does a densifier do, and when do you apply it?

A densifier is a liquid silicate that reacts with free calcium hydroxide inside the concrete to form additional calcium silicate hydrate, filling capillary pores and hardening the surface. Lithium, sodium, and potassium silicate are the three common chemistries, and each system’s manufacturer specifies its own dilution and coverage.

Timing matters more than product choice. Most systems apply the densifier after the metal-bond steps and before the fine resin passes, so the resin tooling is polishing a hardened surface rather than raw paste. Applying it too early wastes product, because the next cutting pass grinds off what it just hardened. Applying it at the very end can leave residue on a closed surface that never reacts.

Application is straightforward: spray it evenly, keep it wet on the surface for the dwell time on the data sheet, work it with a soft brush or microfiber to prevent puddling, and remove any excess before it dries into a white film.

A densified floor also polishes further than an undensified one, which is why the highest gloss levels are only realistic with a densifier in the sequence. It improves abrasion resistance, the property measured by test methods such as ASTM C779.

Should you polish wet or dry?

Wet and dry polishing both work, and the choice comes down to the site rather than the finish. Wet polishing uses water as a coolant and lubricant, which extends tooling life and eliminates airborne dust — at the cost of a slurry that has to be collected and disposed of.

Dry polishing uses HEPA-filtered dust extraction instead of water. It is cleaner for occupied buildings, leaves no slurry, and lets you see the surface as you work, which makes it easier to judge when a grit is finished. Tooling wears faster and the dust collection has to be genuinely effective.

Many crews use both in one job. The metal-bond cutting steps run wet because that is where the heaviest material removal and the shortest tooling life are, then the resin steps run dry so the floor can be inspected and the finish judged accurately.

Slurry is not wash water. It carries fine cement particles and is highly alkaline, so it gets collected with a slurry vacuum and disposed of according to local requirements rather than hosed toward a drain.

How do you control silica dust while polishing?

Control silica dust with engineering controls, because polishing concrete generates respirable crystalline silica in significant quantities. OSHA regulates this work under 29 CFR 1926.1153, which sets a permissible exposure limit of 50 µg/m³ as an 8-hour time-weighted average and an action level of 25 µg/m³.

The standard’s Table 1 lists specified control methods matched to specific tools. For handheld grinders that means either integrated water delivery or a commercially available shroud with a dust collector meeting the standard’s requirements, with respiratory protection required in the circumstances the table describes. Walk-behind grinders and saws have their own entries.

Practical compliance looks like this: a dust extractor sized for the tool, a shroud that actually seals against the floor, HEPA filtration, and filter cleaning that happens on schedule rather than when airflow visibly drops. Shop vacuums are not dust extractors and do not meet the requirement.

Housekeeping matters as much as the tool. Dry sweeping and compressed air are prohibited methods for cleanup where they expose workers, and HEPA vacuuming replaces both. Edge work in corners is where crews get careless and where exposures spike.

How do you know when to move to the next grit?

Move to the next grit when the current one has completely erased the scratch pattern from the previous step. That is the only rule that governs progression, and it is judged by looking, not by counting passes.

Inspect under raking light. Kill the overheads, put a bright light low and nearly parallel to the floor, and look across the surface. Scratches from a coarser grit stand out as directional lines running the wrong way relative to your last pass. If you can see them, the floor is not ready.

Change direction between steps. Running each grit at roughly 90 degrees to the previous one makes leftover scratches obvious, because they point the wrong way against the new pattern.

Do not skip more than one step in the sequence. Jumping from 100 grit straight to 800 seems to save an hour, but the deeper scratches are still there under the shine, and they become visible the moment the floor reaches gloss — at which point the fix is starting over from the grit you skipped.

Edges and the field have to keep pace. Edge grinders cut differently from planetary machines, so check the perimeter under the same raking light before advancing the whole floor.

Common mistakes

• Cutting too deep on the first pass — aggregate exposure is irreversible, and a floor meant to be salt-and-pepper becomes full stone with no way back.
• Skipping grits to save time — the deeper scratch pattern stays under the gloss and shows up only at the end, when redoing it costs far more.
• Applying the densifier at the wrong point — too early and the next cut removes it, too late and it sits on a closed surface as unreacted residue.
• Matching tooling hardness to the wrong slab — soft bond on soft concrete glazes over, hard bond on hard concrete stops cutting entirely.
• Dry grinding with a shop vacuum — respirable silica exceeds OSHA’s limits quickly and the dust spreads through the whole building.