Abrasive Blasting
Abrasive blasting propels media at a surface with compressed air to clean it, strip scale, or produce a uniform matte texture.
- Part
- Finishing
- Revised
- 2026-08-11
At a glance
- Family
- Subtractive
- Typical tolerances
- Cleaning passes remove very little, but aggressive or repeated blasting removes measurable stock; mask any toleranced feature. Anchor profile is specified at 1.5–4.0 mils (38–100 µm) for coating work
- Surface finish
- Typically 125–500 µin (3.2–12.5 µm) Ra depending on media and pressure; specified for coating work as an anchor profile of 1.5–4.0 mils (38–100 µm)
- Typical volumes
- 1 part to continuous automated wheel-blast lines
- Lead time
- Same day to 3 business days at a job shop; on-site structural work is scheduled by area and containment requirements
- Materials
- Metal, Glass, Plastic, Ceramic
What it is
Abrasive blasting propels hard media at a surface with compressed air or a centrifugal wheel to strip scale, rust, old coatings and casting sand, and to leave a clean, uniformly roughened surface. It is the dominant pre-treatment for paint, powder coating and thermal spray, because coating adhesion depends on the mechanical anchor profile that blasting creates.
The specification that matters is not Ra but anchor profile — the peak-to-valley depth of the blasted surface — with 1.5–4.0 mils (38–100 µm) covering most coating requirements, and cleanliness graded against SSPC/NACE standards from brush-off (SP 7) through commercial (SP 6) and near-white (SP 10) to white metal (SP 5). Nozzle pressure typically runs 60–100 psi (4–7 bar) for production cleaning and lower for delicate work. Media choice — aluminum oxide, steel grit or shot, garnet, glass bead, ceramic, plastic, walnut shell or soda — sets both the aggressiveness and whether the process cuts or peens.
How it works
- Contain and mask. Blasting is done in a cabinet, a blast room or on site with containment. Threads, bearing bores, sealing faces, machined datums and any surface that must not lose dimension are masked with plugs, caps, rubber or steel shielding.
- Select the media. Angular media (aluminum oxide, steel grit, garnet) cut and produce a sharp, deep anchor profile. Round media (steel shot, glass bead, ceramic) peen and produce a dimpled, work-hardened surface with a shallower profile. Media size controls profile depth: coarser media, deeper profile.
- Blast. Media is accelerated through a nozzle by compressed air, typically 60–100 psi (4–7 bar) at the nozzle for structural cleaning, or thrown by a centrifugal wheel on automated equipment. Standoff distance and angle control cutting rate — around 45–60° for cleaning, closer to 90° for maximum profile.
- Verify. Cleanliness is compared against the SSPC/NACE visual standards. Profile is measured with replica tape or a depth micrometer. Both are recorded, because a coating warranty usually depends on them.
- Coat promptly. A freshly blasted steel surface is chemically active and flash-rusts within hours in humid conditions. Coating normally follows within the same shift.
Wet and vapor blasting
Introducing water into the stream suppresses dust, eliminates the silica inhalation hazard, and produces a softer, more uniform satin because the water cushions media impact. Vapor blasting is widely used on aluminum castings and engine components where a dry blast would be too aggressive and would embed media.
Cutting versus peening
Angular media removes material. Round media at controlled intensity is shot peening — a distinct process, verified with Almen strips, that deliberately induces compressive residual stress to improve fatigue life. Ordinary blast cleaning also imparts some compressive stress, which is why thin sheet can bow after one-sided blasting.
Design guidelines
Specify profile and cleanliness, not "sandblast"
A usable drawing note names the cleanliness grade (for example SSPC-SP 10 near-white), the anchor profile range (for example 2.0–3.5 mils / 50–90 µm), and the media type. Without those, two shops will produce two different surfaces and the coating supplier cannot warrant either.
Expect Ra to land in a coarse band
Blasted surfaces are rough. Typical blast finishes fall in the 125–500 µin (3.2–12.5 µm) Ra range depending on media and pressure, with heavy grit work coarser still and fine media finer. Ra correlates only loosely with anchor profile, so specify profile for coating work and Ra only for appearance. See the surface finish chart for how that band compares with machined and ground surfaces.
Mask every toleranced or sealing feature
Blasting removes material — little on a cleaning pass, but measurable on repeated or aggressive work — and it destroys a fine finish. Threads, O-ring grooves, bearing seats, dowel holes and gasket faces must be masked or produced after blasting.
Watch distortion on thin sections
One-sided blasting induces compressive stress in the blasted face and bows thin panels. Sheet below roughly 0.030–0.060 in (0.8–1.5 mm) is at risk. Blast both sides, reduce pressure, or use a less aggressive medium.
Match media to substrate
Never blast stainless steel with media that has been used on carbon steel, and never with steel grit or shot, unless the part will be passivated afterward — embedded free iron causes rust spots on an otherwise sound part. Aluminum, brass and plastics embed hard media easily, so glass bead, ceramic, plastic or walnut are preferred. Cast iron and steel take aluminum oxide or steel grit.
Plan for media breakdown and contamination
Media fractures with use and gets finer and sharper, which changes the profile over a run. Production work uses classifiers and controlled media replacement. On critical jobs, specify new or classified media.
| Feature | Recommended | Limit | Why |
|---|---|---|---|
| Anchor profile for coating | 1.5–4.0 mils (38–100 µm) | Match to the coating's data sheet | Too shallow and adhesion fails; too deep and peaks poke through |
| Cleanliness grade | SSPC-SP 6 general, SP 10 for demanding service | SP 5 white metal for immersion | Residual scale and rust undercut the coating |
| Nozzle pressure | 60–100 psi (4–7 bar) | Reduce for thin or soft parts | Pressure drives profile and distortion |
| Minimum sheet thickness | 0.060 in (1.5 mm) for one-sided blasting | 0.030 in (0.8 mm) | Compressive stress bows thin panels |
| Media on stainless | Stainless, ceramic or glass only | Never carbon steel grit | Embedded free iron rusts |
| Time to coating | Same shift | Before visible flash rust | Blasted steel re-oxidizes within hours |
Cost drivers
Blasting is priced by area, by time, or per part depending on whether the work is cabinet, automated wheel, or a blast room. It is inexpensive per square foot but scales badly with handling and masking.
- Handling and setup. A part that goes into a cabinet and comes out in two minutes costs almost nothing. A structural weldment that needs rigging, a blast room and containment costs by the hour.
- Masking. Plugs, caps and shielding are manual work, applied and removed once per part, and they are the largest adder on machined components.
- Media choice and consumption. Aluminum oxide and steel grit are recyclable through classifiers; single-use media such as garnet and soda is consumed per job.
- Containment and disposal. On-site work, lead-containing old coatings and dust control drive the cost far above the blasting itself.
- Verification. Replica tape profile readings and documented cleanliness grades on every lot add inspection time.
Cost-reduction tactics:
- Specify the loosest cleanliness grade the coating system actually requires — SP 10 costs materially more than SP 6.
- Design so that toleranced features can be machined after blasting rather than masked during it.
- Batch parts of the same media type together to avoid media changeovers.
- Use recyclable media on repeat production work and reserve single-use media for jobs that require it.
- Where the requirement is only cosmetic uniformity on small parts, price vibratory finishing or bead blasting against a manual blast operation.
Questions
6 questionsWhat surface finish does abrasive blasting produce?
Typically 125–500 µin (3.2–12.5 µm) Ra depending on media and pressure, with heavy grit work coarser and fine media finer. For coating work the meaningful specification is anchor profile — the peak-to-valley depth — usually 1.5–4.0 mils (38–100 µm), measured with replica tape rather than a profilometer.
What is the difference between SSPC-SP 6, SP 10 and SP 5?
They are cleanliness grades. SP 6 (commercial blast) allows light staining over a limited portion of the surface, SP 10 (near-white) allows less, and SP 5 (white metal) requires the surface be free of all visible residue. Cost rises steeply from SP 6 to SP 5, so specify the grade the coating system actually needs.
Which blast media should I use?
Angular media — aluminum oxide, steel grit, garnet — cuts and creates a sharp, deep anchor profile for coating. Round media — steel shot, glass bead, ceramic — peens and gives a shallower, satin surface. Media size controls profile depth, and soft substrates such as aluminum and plastics need non-embedding media such as glass bead, plastic or walnut shell.
Can stainless steel be abrasive blasted?
Yes, but only with media that has never touched carbon steel, and never with steel grit or shot unless the part will be passivated afterward. Embedded free iron rusts and produces surface corrosion on an otherwise sound stainless part.
Will blasting distort thin parts?
It can. Blasting induces compressive stress in the treated face, so one-sided blasting bows thin panels — sheet below roughly 0.030–0.060 in (0.8–1.5 mm) is at risk. Blast both sides, drop the pressure, or switch to a less aggressive medium.
How soon after blasting must a part be coated?
Within the same shift in most conditions. A freshly blasted steel surface is chemically active and flash-rusts within hours in humid air, and any visible rust bloom means the surface has to be reblasted before coating.