Concrete

Scarifying: Cutter Types and When to Use Them

How scarifiers work, which cutters to use for coatings, leveling and general prep, setting depth on National's Spartans, and the CSP, silica and noise rules.

Updated · 3 min read

A scarifier (also called a surface planer or milling machine) spins a drum of loose cutters that strike and chip the surface. It removes thicker coatings, line striping and high spots faster than a grinder, but leaves a rougher profile. The cutter type decides how aggressive it is.

Silica and noise

OSHA Table 1 lets walk-behind milling machines run with an integrated water system, or with the manufacturer's recommended dust collector (at least its recommended airflow, a filter of 99% or better and a filter-cleaning mechanism), plus HEPA vacuuming between passes indoors.[1] The National DL2000 is the recommended collector for both Spartans. The Spartan can reach 100 dB(A), so hearing protection is mandatory.[4] OSHA's limit at 100 dBA is 2 hours.[2]

How a scarifier cuts

Loose cutters ride on axles in a drum, and the drum's rotation throws them against the surface.[4] The cutters need about 1/8" to 3/16" of side play on their axles to work.[4]

Cutter types

Cutters are grouped by material, and each suits a different job.[3]

Cutter Use
Tungsten carbide (HMR) Leveling concrete or asphalt, grooving, line removal, sidewalk trip hazards and stubborn thinset
Steel (TSR) Thin coatings, glue, mastic, line striping and general concrete prep; leaves a profile like shot blasting
Milling (TMO) Thicker, softer material with little damage to the surface; epoxy, thermoplastic, line striping, waterproofing membranes

Published guidance isn't fully consistent on leveling: one cutter list assigns it to carbide, while a quick guide on the same page says milling cutters.[3] Test on the actual job. For thick epoxy and elastomerics, see Removing epoxy and coatings.

Setting depth

Depth is the most important setting.[4]

  • Set the depth so the cutters scratch the surface as deep as the job needs and no deeper.
  • The cutters have to fly freely and turn on their axles. At the right depth, the machine runs quietly and evenly.
  • If the depth is set too deep, the cutters jam and the machine runs rough and jumps.

Step by step (National Spartan)

This is the start-up sequence for the Spartan.[5]

  1. Turn on the dust collector.
  2. With the drum raised, turn the depth setting fully counter-clockwise.
  3. Start the machine, release the brake and lower the drum slowly.
  4. Set the depth with the hand wheel until the machine runs smoothly.
  5. Move forward at a rate that suits the material and profile. A push-pull motion often works best.[5]
  6. Use the quick lifter to raise the drum without changing the depth setting.

The profile you'll get

Scarifying leaves a coarse profile, and sources give different ranges.

  • ICRI 310.2R puts scarifying at about CSP 4 to 7.[6]
  • One coatings maker lists scarifying at CSP 6 to 9, and requires shot blasting afterward for its systems because scarifying can damage and loosen the top layer of concrete.[7]
  • Grinders suit CSP 1 to 3; for higher profiles, a scarifier or shot blaster may be the better tool.[8]

See ICRI CSP profiles and Shot blasting basics.

Maintenance

Worn cutters unbalance the drum.

  • Inspect cutters often, rotate them so they wear evenly, and replace them when they stop cutting well.[3]
  • Excessive vibration usually means worn or broken cutters; replace them all.[4]
  • Check the drum, axles, cutters, housing and gear belt tension daily. When changing drums, clean and lubricate the drive shaft.[4]
  • Non-original parts and cutters void the warranty.[4]

Common mistakes

These wear out cutters and leave a poor surface.

  • Setting depth too deep. The machine jumps and the cutters block.
  • Wrong cutter for the job. It's a common cause of poor performance.[3]
  • Leaving the scarified surface as-is when the coating system requires blasting.
  • Standing too close. Stay at least 3 ft from the machine while it runs.[4]

Equipment we carry

These are the scarifiers, drums and dust collector we stock.

Regulations and references

  1. OSHA 1926.1153, Silica, including Table 1
  2. OSHA 1926.52, Occupational noise exposure
  3. National: What cutter do I need on my scarifier?
  4. National Spartan 220 manual
  5. National Spartan 110 manual
  6. ICRI: Concrete Repair Bulletin on ICRI 310.2R
  7. Sika: Surface preparation guide
  8. National Flooring Equipment: Concrete grinder training guide
  9. National Flooring Equipment: Grinder tooling guide

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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