Concrete

Polishing Concrete: Grit Sequence and Densifier

The grind-hone-polish sequence, when and how to apply densifier, lithium vs sodium silicate, gloss targets, and dust and slurry rules for polished concrete.

Updated · 3 min read

Polished concrete is a sequence: grind with metal bonds, densify, hone with resin, then polish with finer resin to the gloss you want. Each step removes the scratch from the one before. The densifier goes on in the 50 to 200 grit range, depending on the manufacturer.

Silica and slurry

OSHA Table 1 lets walk-behind floor grinders run wet, or dry with the manufacturer's recommended dust collector (filter of 99% or better with a filter-cleaning mechanism) and HEPA vacuuming between passes indoors.[1] If you grind wet, extract the slurry and dispose of it properly.[2] The National Helix and 8274-4 are not for wet locations.[8]

Before you start

Check the slab and plan the finish before the first pass.

  • Don't polish green concrete; it has to be fully cured first.[3]
  • Ameripolish requires new slabs to cure at least 28 days before its densifier.[6]
  • Test hardness to choose the bond. If the tooling wears more than 1 mm in the first 30 minutes, the bond is probably too hard.[2] See Diamond bond and grit selection.
  • Decide on aggregate exposure first. The usual classes are cement fines (up to 1/16" removed), fine aggregate (1/8") and coarse aggregate (1/4").[2]

The sequence

The process breaks into three stages.[2]

Stage Grit Tooling
Grinding #25 to 100 Metal bond
Honing #100 to 400 Resin or hybrid
Polishing #800 to 3000 Resin
  • Make each pass perpendicular to the last, and get everything you can out of each grit before moving to the next.[2]
  • Clean the floor thoroughly after each pass so debris doesn't scratch it.[3]
  • The machines top out at different grits: the National Helix polishes to a 400 grit finish and the 8274-4 to 1500.[3]
  • If you're making dust, you're grinding. If not, the machine is just riding over the surface, so change the tooling.[3]

Densifier

Densifier reacts with the concrete to harden the surface, giving higher density, lower porosity, less dusting and better wear resistance.[2]

Maker When Keep wet
Husqvarna After the last metal step (#100)[2] 15 to 20 minutes
PROSOCO Consolideck LS At a 50 to 200 grit finish[4] 5 to 10 minutes
Ameripolish 3D HS After grinding up to 200 resin[6] 15 minutes
  1. Clean the floor. Ameripolish uses an auto scrubber and fresh water, then lets the floor dry.[6]
  2. Spray the densifier on and spread it with a microfiber pad or mop. Keep adding it until the floor stops taking it in.[2]
  3. Keep the surface wet for the maker's time, spreading puddles. Puddles slow drying and leave white residue that has to come off right away.[4]
  4. Let it dry, usually about 8 to 12 hours.[2]
  5. Continue honing and polishing.

Lithium vs sodium silicate

Both react with the concrete, but they handle differently.

  • Lithium silicate is marketed as safer, faster and easier to apply than sodium or potassium silicate hardeners, with no scrubbing, flushing or caustic wastewater.[4]
  • Sodium silicate adds silica that reacts with the excess calcium hydroxide in the concrete to form more CSH.[7]

Gloss targets and guard

Gloss is measured before any guard or sealer, and the levels below line up with the Concrete Polishing Council's appearance levels.[2]

  • Matte: below 10 gloss units, stopping at #100 resin (CPC level 1 or below).
  • Satin: 20 or more, usually up to #400 (CPC level 2 or above).
  • High gloss: 50 or more, usually up to #1500 (CPC level 3 or above).
  • If you hit the target finish at an earlier step, you don't have to run the rest of the sequence.[2]
  • Guard: don't pour guard straight onto the floor, which can darken spots.[2] Two thin coats work better than one heavy coat.[5]

Common mistakes

These cost the most time.

  • Moving on before the scratch is gone. It shows at high gloss.
  • Densifying too late or letting it puddle.
  • Skipping cleanup between grits.
  • Polishing green concrete.
  • Running a dry-only machine wet.

Equipment we carry

We carry grinders, tooling and dust collection; we don't sell densifiers or guards.

Edges are covered in Edge grinding and tooling in Diamond tooling types.

Regulations and references

  1. OSHA 1926.1153, Silica, including Table 1
  2. Husqvarna: Polished concrete specification
  3. National Flooring Equipment: Grinder tooling guide
  4. PROSOCO Consolideck LS data sheet
  5. PROSOCO PolishGuard data sheet
  6. Ameripolish 3D HS data sheet
  7. Euclid Chemical: Reactive sealers
  8. National 8274-4 operating and service manual

Linked PDF documents are archived copies saved by PreFloor Tools so they stay available if the publisher moves or removes them. Check the publisher's website for the latest revision.

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