Concrete

Shot Blasting: Shot Size, Travel Speed and Profile

How shot size, travel speed and machine setup control the profile a shot blaster leaves, plus magnets, dust collection and edges.

Updated · 2 min read

A shot blaster throws steel shot at the slab, recovers it, and throws it again, removing laitance and thin coatings and leaving a uniform profile. You control the result with two things: the size of the shot and how fast you walk.

Silica

Shot blasting releases respirable crystalline silica. Run it with a matched dust collector and follow OSHA 1926.1153.[7] See Silica dust and respiratory safety.

What profile to expect

Shot blasting is a mid-range profile method. Under ICRI 310.2R, shot blasting can produce CSP 2 to 9[2]; one manufacturer's guide narrows that to CSP 3 to 7.[5] See ICRI CSP profiles for what those numbers mean.

Shot size

Bigger shot hits harder and leaves a deeper profile. This is the shot guide for the National A95, an 8" blaster.[1]

Goal Shot
Brush blast, penetrating sealer S-280 to S-330
Worn surfaces, tile mastic, urethane, epoxy S-330

The A95 isn't recommended for urethane over 10 mil or for removing 1/8" or more of concrete.[1] Always check your machine's manual for the shot sizes it's built for.

Travel speed

A light profile takes a faster travel speed than a coarse one.[3] Start with a lower feed rate, and don't stop mid-pass or you'll leave ridges.[4] Do a test pass and compare it to CSP chips before running the whole floor.

Setup

A few setup steps make the machine work properly from the first pass.

  1. Charge the magnets with a layer of shot before starting.[6]
  2. Load shot per your machine's manual.
  3. Connect a dust collector matched to the blaster. The A95 is paired with the National DL2000.[1]
  4. Run a test strip, check the profile, and adjust speed or shot.

Edges and cleanup

Blasters don't reach the wall.

  • Grind the edges with a shrouded hand grinder to match the profile.
  • Pick up loose shot with a hand magnet before anything else goes down.
  • Blasting follows the surface; it doesn't flatten it. See Choosing a prep method.

Common mistakes

These cause most uneven blast patterns.

  • Stopping in the middle of a pass. It leaves a deep spot.
  • Wrong shot for the goal. Too big over-profiles thin systems.
  • Undersized dust collector.
  • Leaving shot on the floor. It ends up under the flooring.

Equipment we carry

These are the blaster and shot we stock.

References

  1. National Flooring Equipment: A95 shot blaster performance guide
  2. ICRI: Concrete Repair Bulletin on ICRI 310.2R
  3. Husqvarna: Blastrac 1-8DPS operating instructions
  4. National Flooring Equipment: Shot blasting tips
  5. Sika: Surface preparation guide
  6. National Flooring Equipment: Shot blasting 101, charge your magnets
  7. OSHA 1926.1153, Silica in construction

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.

Tools for this job

Shop by category

More Concrete guides