How to Choose Aluminum Oxide Blast Media for Steel Surfaces

A practical, specification-grade guide for coating contractors, fabrication engineers, and procurement professionals — covering steel type, contamination grade, cleanliness standards, grit selection, blast parameters, and quality verification.

By Jiangsu Henglihong Technology Co., Ltd. March 2026 ~4,400 words · 16 min read

Table of Contents

Why Steel Surface Preparation Is Different from Other Substrates
Steel Type Determines Grade Selection
Understanding Cleanliness Standards: SSPC, ISO & NACE
Assessing Initial Surface Condition
Grit Size Selection for Steel: A Decision Framework
Blast Parameters for Steel Applications
Recommendations by Steel Application Type
Quality Verification Before Coating
Troubleshooting Common Blasting Problems on Steel
Questions fréquemment posées

1. Why Steel Surface Preparation Is Different from Other Substrates

Steel is by far the most common substrate for aluminum oxide blast media applications worldwide — and it is also the substrate where specification errors carry the highest financial consequences. A poorly prepared steel surface leads to premature coating failure, corrosion penetration into the substrate, and costly maintenance interventions — sometimes within months of initial coating application.

What sets steel apart from glass, ceramics, or aluminum as a blast substrate is the combination of three simultaneously active variables: the type and extent of surface contamination (mill scale, rust grades A through D, old paint, oil, salts), the mechanical properties of the steel itself (hardness, section thickness, grain structure), and the service environment demands placed on the coating system that will be applied afterward. Getting the media selection right means addressing all three at once.

SP 5 Highest cleanliness grade

F16–F36 Most common grit range

40–100 µm Typical anchor profile Rz

60–100 PSI Standard blast pressure

4–8× Media recyclability

This guide is written for practitioners working with carbon steel, structural steel, stainless steel, cast iron, and galvanized steel — the five substrate types that account for the vast majority of aluminum oxide blast media consumption. For the full product background on aluminum oxide blast media, see: Aluminum Oxide Blast Media: The Complete Buyer’s Guide.

2. Steel Type Determines Grade Selection

The first decision in any steel blasting specification is determining the steel type — because this directly governs whether you should specify brown fused or white fused aluminum oxide. Using the wrong grade on an iron-sensitive steel type is the most expensive specification error in this category, generating re-work costs that routinely reach two to five times the original surface preparation budget.

CS

Carbon & Low-Alloy Steel

Structural sections, plate, pipe, fabricated components. The largest volume application. Iron contamination from abrasive is inconsequential — substrate is itself ferrous.

Use: Brown Fused Al₂O₃

SS

Stainless Steel

Austenitic (304, 316), duplex (2205), super-duplex (2507). Passive chromium oxide film. Iron contamination from brown-grade abrasive initiates corrosion halos and film breakdown.

Use: White Fused Al₂O₃ only

CI

Cast Iron

Pump housings, valve bodies, engine blocks, pipe fittings. Hard surface with graphite inclusions. Brittle — sensitive to over-blasting at high pressure.

Use: Brown Fused, lower pressure

HW

Hardened & Tool Steel

Above 45 HRC. Dies, molds, wear plates, shafts. Requires media harder than the substrate — only aluminum oxide (Mohs 9) cuts effectively above 55 HRC.

Use: Brown or White, coarser grit

GS

Galvanized Steel

Zinc-coated structural steel. Sweep blast only — do not remove the zinc layer. Purpose is to dull the surface and improve overcoat adhesion.

Use: Brown or White, fine grit, low pressure

Critical rule for stainless steel: Never use brown fused aluminum oxide on stainless, duplex, or super-duplex steel. The Fe₂O₃ particles embedded during blasting destroy the passive film, causing rust halos that are invisible at inspection but progressive in service. Always specify white fused aluminum oxide and verify with a ferroxyl test before coating. For a full technical explanation of the failure mechanism, see: Brown vs White Aluminum Oxide: Which Should You Use?

3. Understanding Cleanliness Standards: SSPC, ISO & NACE

Before selecting grit size or blast pressure, you must identify the cleanliness grade required by the coating manufacturer’s Product Data Sheet (PDS) or the project specification. Cleanliness grade and anchor profile depth are the two outputs that must be achieved simultaneously — grit selection influences both.

SSPC-SP 5
ISO Sa 3

White Metal Blast — The highest standard

Complete removal of all visible rust, mill scale, paint, and foreign matter. Metal surface has a uniform gray-white appearance. Required for immersion service (tank linings, offshore splash zones, chemical plant), buried pipelines, and high-build coating systems above 400 µm DFT. The most demanding and most expensive to achieve.

Recommended grit: F16–F24 brown Al₂O₃ at 80–100 PSI

SSPC-SP 10
ISO Sa 2½

Near-White Metal Blast — The workhorse standard

Minimum 95% of each unit area free of all visible contamination. Light staining of rust or mill scale on the remaining 5% is permissible. The most widely specified grade for industrial protective coatings: marine topside, industrial atmospheric exposure, moderate-service tank coatings. Best balance of cost and protection.

Recommended grit: F24–F36 brown Al₂O₃ at 70–90 PSI

SSPC-SP 6
ISO Sa 2

Commercial Blast — General industrial standard

Minimum two-thirds of each unit area free of all visible contamination. Traces of mill scale, rust, and old coatings may remain in pits. Acceptable for general industrial atmospheric service, non-immersion, light-duty protective coatings where some contamination tolerance is permissible under the specification.

Recommended grit: F36–F46 brown Al₂O₃ at 60–80 PSI

SSPC-SP 7
ISO Sa 1

Brush-Off Blast — Light cleaning only

Loosely adhering mill scale, rust, and paint removed. Tightly adherent contaminants may remain. Used for atmospheric exposure maintenance painting, shop primer over new steel, or where the coating system tolerates minimal surface preparation. Not appropriate for immersion or aggressive service environments.

Recommended grit: F46–F60 brown Al₂O₃ at 40–60 PSI

SSPC-SP 11
Power Tool

Power Tool Cleaning to Bare Metal — No blast media required

Achieves bare metal by mechanical means when blasting equipment is not available. Included here for reference — achieves a profile of approximately 25–40 µm maximum with power tools, which is insufficient for many high-performance coating systems. Blasting with Al₂O₃ invariably produces a superior result where equipment is accessible.

Not applicable — blast media not used

How to find the required cleanliness grade: The coating manufacturer’s Product Data Sheet (PDS) will specify the minimum surface preparation standard under a section typically headed “Surface Preparation” or “Substrate Conditions.” If the PDS gives a range (e.g. “minimum SSPC-SP 6, recommended SSPC-SP 10”), always target the higher standard — the additional preparation cost is far less than the cost of early coating failure attributable to under-preparation.

4. Assessing Initial Surface Condition

The initial condition of the steel surface — specifically its rust grade and mill scale coverage — directly affects the grit size you need and the blast time required per square meter. ISO 8501-1 defines four rust grades for steel prior to blasting, illustrated with photographic reference standards:

ISO Rust Grade	Surface Description	Mill Scale Status	Recommended Grit	Expected Blast Time
Grade A	Steel with intact mill scale; little or no rust visible	Fully adherent, continuous	F16–F24	Longer — scale must be mechanically broken
Grade B	Steel with some rust; mill scale beginning to flake	Partially adherent, starting to peel	F24–F36	Modéré
Grade C	Steel with rust; mill scale mostly removed by rusting	Mostly gone — rust throughout	F24–F36	Moderate — rust removal more efficient than scale
Grade D	Steel with deep pitting and rust; no mill scale remaining	Absent — deep corrosion pits present	F36–F46	Shorter overall, but pits need multiple passes

Mill Scale: Why It Demands Special Attention

Mill scale is a thin layer of iron oxides (primarily magnetite, Fe₃O₄) that forms on the surface of hot-rolled steel during the manufacturing process. It is harder than the steel beneath it — approximately 500–600 HV versus 150–200 HV for mild steel — and is electrically cathodic relative to the underlying steel. This means mill scale, when left in place under a coating, acts as a cathode and drives accelerated anodic corrosion of the underlying steel at any point where the coating is breached. Removing mill scale completely is therefore not merely a surface cleanliness requirement — it is a corrosion protection requirement.

Mill scale is best removed with a coarser grit at higher pressure. For Grade A steel (intact mill scale), F16–F24 at 80–100 PSI is the standard approach. The angular grain of aluminum oxide is particularly effective at fracturing and undercutting scale — it physically wedges under scale edges and levers the scale free rather than simply abrading the top surface.

Salt contamination — the invisible threat: Soluble salts (chlorides, sulfates, nitrates) on a steel surface are invisible to the naked eye and are not removed by blasting alone. They cause osmotic blistering under coatings — a failure mode that presents as circular domes of lifted coating filled with corrosive liquid. Before blasting any steel that has been in atmospheric or marine service, test for soluble salt contamination using Bresle patch method (ISO 8502-6) or equivalent. If salt levels exceed 20–50 mg/m² (the typical threshold for immersion or aggressive service specifications), the steel must be fresh-water washed and dried before blasting. Blasting over high-salt steel merely embeds the salts in the anchor profile valleys — producing a surface that passes visual inspection but fails prematurely in service.

5. Grit Size Selection for Steel: A Decision Framework

Selecting the correct grit size for a steel blasting job requires integrating four pieces of information: the required cleanliness grade, the target anchor profile depth, the steel substrate type (hardness and section thickness), and the equipment type. The table below consolidates these variables into a practical decision matrix for the most common steel blasting scenarios.

Application	Steel Type	Target Rz	Grade	FEPA Grit	Pressure
Structural steel — SP 5 / immersion	Carbon steel, Grade A–B	70–100 µm	Marron	F16–F24	80–100 PSI
Structural steel — SP 10	Carbon steel, Grade B–C	50–75 µm	Marron	F24–F36	70–90 PSI
Structural steel — SP 6	Carbon steel, Grade C–D	35–55 µm	Marron	F36–F46	60–80 PSI
Pipeline — external FBE coating	Carbon steel pipe	50–75 µm	Marron	F24–F36	70–90 PSI
Tank lining — immersion service	Carbon steel, Grade A	65–90 µm	Marron	F16–F24	80–100 PSI
Stainless steel — general industrial	304 / 316 SS	25–45 µm	Blanc	F46–F80	50–70 PSI
Stainless steel — food / pharma	316L / duplex	20–35 µm	Blanc	F60–F80	40–60 PSI
Cast iron — pump / valve body	Grey / ductile cast iron	40–65 µm	Marron	F24–F46	50–70 PSI
Hardened steel — mold / die	Tool steel, 45–65 HRC	30–55 µm	Brown or White	F36–F60	60–80 PSI
Galvanized steel — sweep blast	Hot-dip galvanized	15–30 µm	Brown or White	F46–F80	30–50 PSI
Thermal spray bond coat prep	Carbon / alloy steel	55–80 µm	Blanc	F24–F36	70–90 PSI
Powder coating prep — thin section	Mild steel sheet <3 mm	25–40 µm	Marron	F46–F60	40–60 PSI

For the complete engineering reference covering all FEPA grit sizes, particle size data, and anchor profile depth ranges, see: Aluminum Oxide Grit Size Chart & Selection Guide.

6. Blast Parameters for Steel Applications

Grit size is the primary driver of anchor profile depth, but blast parameters — pressure, nozzle geometry, standoff distance, and nozzle angle — determine how much of the grit’s profile potential is realized. For steel applications specifically, these parameters also govern whether tightly adherent mill scale and hard rust layers are physically removed or merely polished.

Blast Pressure

Higher pressure accelerates media velocity and increases both cutting aggression and profile depth — but with diminishing returns above approximately 90 PSI (6.2 bar) for most aluminum oxide grits on steel. Beyond this threshold, additional pressure primarily increases media fracture rate, shortens nozzle life, and raises compressor energy cost without proportionally increasing profile depth or cleanliness grade. The practical working range for steel preparation is:

40–60 PSI (2.8–4.1 bar): light sweep blast, galvanized steel, thin sheet metal
60–80 PSI (4.1–5.5 bar): general SP 6 / SP 10 work on moderate rust and scale
80–100 PSI (5.5–6.9 bar): SP 5 / heavy mill scale / Grade A steel

Nozzle Type and Bore Diameter

For open-blast steel work, venturi-profile nozzles (also called laval nozzles) significantly outperform straight-bore nozzles. A venturi nozzle accelerates the media stream through a converging-diverging profile, producing exit velocities 40–60% higher than a straight-bore nozzle at the same inlet pressure. This translates directly into faster cleaning rates and deeper profiles per unit of media consumed. The nozzle bore diameter must be matched to the grit size: as a rule, the bore should be at least four to five times the D90 particle diameter to prevent bridging and inconsistent flow.

FEPA Grit	D90 Particle Size	Minimum Nozzle Bore	Recommended Bore	Replace Nozzle When Bore Reaches
F16	~1,700 µm	9 mm (⅜ in)	10–11 mm	12–12.5 mm (+25%)
F24	~1,000 µm	6 mm (¼ in)	7–8 mm	9 mm (+25%)
F36	~710 µm	4 mm	6–7 mm	7.5–8 mm (+25%)
F46–F60	~500 µm	3 mm	5–6 mm	6.5–7 mm (+25%)

Standoff Distance and Nozzle Angle

The optimal standoff distance for most steel blast work is 20–30 cm (8–12 inches) measured from nozzle tip to substrate. Shorter distances increase impact energy per unit area but reduce coverage rate and risk over-blasting on thin sections. Longer distances improve coverage rate but reduce profile depth — useful when a shallower profile is required without stepping to a finer grit.

Nozzle angle affects the cutting mechanism. A 90° perpendicular angle maximizes compressive impact energy and is preferred for deep profile generation and mill scale removal. A 15–30° oblique angle introduces a shearing component that is more effective at undercutting and removing tightly adherent scale and old paint at the edges of pits and surface irregularities. Many experienced blasters use a combination — perpendicular passes for initial cleaning, followed by oblique passes to clean out pit bottoms and recesses.

7. Recommendations by Steel Application Type

Structural Steel and Bridge Fabrication

This is the highest-volume application for aluminum oxide in steel surface preparation. New fabrication typically presents Grade A–B steel (intact or partially scaled mill scale). Brown fused aluminum oxide at F24–F36, 70–90 PSI, achieves SSPC-SP 10 in a single pass on most grades of structural mild steel — the most commonly specified standard for bridge and building structural coatings. For aggressive environments (marine atmosphere, acid industrial atmosphere), SP 5 may be required, in which case step up to F16–F24 at 85–100 PSI.

Pipeline and Vessel Coating

Pipeline coating specifications — particularly for fusion-bonded epoxy (FBE), three-layer polyethylene (3LPE), and liquid epoxy internal linings — are among the tightest in the industry. Most pipeline coating standards require SP 10 minimum with a specific anchor profile tolerance: typically 40–70 µm for FBE and 50–80 µm for liquid internal coatings. F24–F36 brown fused aluminum oxide in a centrifugal blast machine (wheelblast) or direct-pressure portable unit is the standard specification. Wheelblast systems in pipe coating plants typically use F24–F30 to achieve consistent profiles across the pipe circumference in a single pass.

Storage Tank Linings — Immersion Service

Tanks storing water, chemicals, hydrocarbons, or food products require the most demanding surface preparation — invariably SP 5 (White Metal) with an anchor profile of 65–100 µm depending on the lining system thickness. Brown fused aluminum oxide F16–F24 at 85–100 PSI is the specification of choice. The angular grain of aluminum oxide is particularly critical here: the sharp peaks of the anchor profile create maximum mechanical adhesion for thick film novolac epoxy, glass flake epoxy, and vinyl ester lining systems that may be 500–2,000 µm DFT.

Stainless Steel Process Equipment

Food and beverage vessels, pharmaceutical reactors, and chemical process columns in stainless steel require white fused aluminum oxide — no exceptions. The typical specification is F46–F80 at 50–70 PSI for general industrial stainless, and F60–F80 at 40–60 PSI for pharmaceutical-grade or food-contact surfaces. Post-blast verification with a ferroxyl test is mandatory before any coating application. For detailed guidance on stainless steel applications, see our aerospace and medical-grade media article: Aluminum Oxide Blast Media for Aerospace & Medical.

Powder Coating Preparation

Powder coating adhesion on mild steel requires a clean, oxide-free surface with moderate anchor profile — typically 20–40 µm for standard industrial powder. Thin-section sheet metal (1–3 mm) is sensitive to distortion from excessive blast pressure or coarse grit. F46–F60 brown fused aluminum oxide at 40–60 PSI in a suction-feed blast cabinet is the standard for most powder coat pre-treatment work. The key quality criterion before powder coating is surface cleanliness (SP 10 or better) and absence of oil — outgassing from residual oil beneath a cured powder coat causes fish-eye defects that cannot be repaired without stripping and recoating.

8. Quality Verification Before Coating

A correctly blasted steel surface must be verified against specification before any coating is applied. Coating application over a non-conforming surface — regardless of how good the coating system is — will result in premature failure. The following is the minimum verification sequence for specification-grade steel blasting work.

1

Visual cleanliness assessment

Compare the blasted surface against ISO 8501-1 photographic standards or SSPC Visual Standards. Confirm the achieved cleanliness grade meets or exceeds the specification requirement. Inspect under adequate lighting (minimum 500 lux at the surface) from multiple angles. Check for residual mill scale in pits and recesses — these areas are commonly missed in a single-direction blast pass and must be re-blasted.

2

Anchor profile measurement

Measure surface anchor profile depth (Rz) using ISO 8503 replica tape (Testex Press-O-Film or equivalent) or a calibrated electronic profilometer (ASTM D4417 Method C). Take a minimum of five independent readings per inspection lot, spaced at least 0.5 m apart. Calculate the mean Rz and confirm it falls within the tolerance band specified in the coating PDS. Record all readings in the Quality Control documentation for the project.

3

Soluble salt test

For immersion service, offshore, or any specification that includes a salt contamination limit: test using the Bresle patch method (ISO 8502-6 / ASTM D4940) or equivalent. Compare the result against the project specification limit — typically 20 mg/m² (as NaCl equivalent) for immersion service, 50 mg/m² for atmospheric service. If the limit is exceeded, fresh-water wash, dry, and re-blast before re-testing.

4

Dew point and humidity check

Measure ambient temperature, steel surface temperature, relative humidity, and dew point using a calibrated sling psychrometer or digital hygrometer. Most specifications require the steel surface temperature to be at least 3 °C above the dew point and relative humidity below 85% before coating can proceed. Failing to check this is the most common cause of adhesion failure on otherwise correctly prepared surfaces — flash rust forms within minutes on freshly blasted steel under adverse dew point conditions.

5

Ferroxyl test — stainless steel only

For any stainless steel substrate blasted with white fused aluminum oxide: apply the ferroxyl indicator solution (potassium ferricyanide in dilute nitric acid) to the blasted surface via wipe or spray and observe for color change within 30–60 seconds. A blue-green color indicates the presence of surface iron contamination — requiring re-blasting with verified clean white grade media from dedicated equipment. A negative (no color change) result clears the surface for coating. Document the test result and the abrasive CoA as part of the inspection record.

6

Time to first coat

Freshly blasted carbon steel begins to re-rust within 2–4 hours in humid outdoor conditions, and within 30–60 minutes in marine or industrial atmospheres. Most coating specifications require the first coat to be applied within 4 hours of blasting in normal atmospheric conditions, and within 1–2 hours in aggressive environments. If this window cannot be maintained, re-blast and re-inspect before coating. Never apply coating over visible flash rust without obtaining written approval from the coating manufacturer and recording the deviation in the QC documentation.

9. Troubleshooting Common Blasting Problems on Steel

Problem Observed	Most Likely Cause	Corrective Action
Profile too shallow — Rz below specification	Grit too fine; blast pressure too low; nozzle worn; media degraded below effective D50; standoff too great	Step up grit size or increase pressure; measure nozzle bore and replace if worn beyond 25% of nominal; top up media charge; reduce standoff distance
Profile too deep — Rz above specification ceiling	Grit too coarse; blast pressure too high; standoff too short; multiple overlapping passes on same area	Step down grit size; reduce pressure; increase standoff; move nozzle at consistent rate; use a single pass strategy
Residual mill scale in pits and seams	Single-direction blast pass; perpendicular-only nozzle angle; pressure too low for Grade A scale	Add oblique-angle pass (15–30° off perpendicular) after primary pass; increase pressure to 85–100 PSI for intact scale; use coarser grit (F16–F24)
Flash rust forming before coating	Time between blasting and coating exceeded; humidity above dew-point control threshold; salt contamination not removed	Reduce time-to-coat; check and enforce dew-point conditions; test and treat for soluble salts before blasting; schedule blasting immediately before coating window
Rust halos appearing on stainless steel after coating	Brown fused aluminum oxide used instead of white; cross-contamination from shared equipment; ferroxyl test not performed	Strip coating; re-blast with white fused Al₂O₃ on dedicated clean equipment; perform and record ferroxyl test; review procurement and equipment protocols
Inconsistent anchor profile across the work area	Nozzle worn unevenly; media size distribution drifted; operator speed inconsistent; air supply pressure fluctuating	Replace nozzle; top up with fresh media; calibrate air supply pressure; train operators on consistent nozzle travel speed and pattern overlap
Substrate distortion on thin-section steel	Grit too coarse for section thickness; blast pressure too high; excessive dwell time per area	Step to finer grit (F46–F60); reduce pressure to 40–55 PSI; increase nozzle travel speed; blast from both sides alternately on thin sections
Media bridging in blast cabinet hopper	Media moisture content too high; grit too fine clumping under compression; hopper geometry inadequate for fine grits	Dry media before use (110 °C / 2 hours if severely damp); specify media moisture ≤0.3% on CoA; install vibrating hopper agitator for fine-grit applications

10. Frequently Asked Questions

SSPC-SP 10 (Near-White Metal Blast, equivalent to ISO Sa 2½) requires that at least 95% of each unit area of the surface is free of all visible contamination — allowing light staining of rust or mill scale on the remaining 5%. SSPC-SP 5 (White Metal Blast, ISO Sa 3) requires 100% removal of all visible contaminants with no staining permissible. SP 5 is required for immersion service (tank linings, buried pipelines, offshore submerged zones, chemical plant vessels), where even minor residual contamination under a high-build coating will initiate osmotic blistering. SP 10 is the standard for most atmospheric-exposure structural steel, marine topside, and general industrial protective coating. SP 5 adds approximately 25–40% to blast time and media consumption compared to SP 10 — cost it into the specification before mandating it.

Yes, aluminum oxide is compatible with centrifugal wheelblast machines, which are widely used in pipe coating plants, steel service centers, and structural fabrication shops for high-volume continuous processing. The key consideration is that aluminum oxide’s higher hardness (Mohs 9) causes higher wear rates on wheelblast impellers, control cages, and blades compared to steel grit or steel shot. Tungsten carbide-lined or ceramic-lined blast wheels are recommended when running aluminum oxide continuously to achieve acceptable component life. The economics are typically favorable despite higher wear costs, because aluminum oxide’s media efficiency (faster cleaning, better profile consistency, multi-cycle recyclability) offsets the component maintenance cost at production volumes above approximately 200–300 m²/day.

The only reliable indicator is anchor profile measurement — not visual inspection of the media or elapsed time. Measure the achieved Rz using ISO 8503 replica tape at the start of each production shift, and again midway through if processing more than 100 m² per shift. When the mean Rz across five readings drops below the lower tolerance in your coating PDS, it is time to top up with fresh media. A secondary indicator is increased blast time required to achieve SP 10 on equivalent steel grades — this signals that the cutting efficiency of the media charge has degraded. Keep a production log of Rz readings versus cumulative blast area to predict top-up intervals on an empirical basis rather than guessing. For detailed guidance on media life management, see: Is Aluminum Oxide Blast Media Reusable? How Many Times?

Flash rust prevention requires managing three variables simultaneously: time, humidity, and salt contamination. Apply the first coat within the window specified in the coating PDS — typically 4 hours maximum at <60% RH, 2 hours at 60–85% RH, and sometimes as short as 30 minutes in marine conditions. Use a dew-point instrument (digital hygrometer with thermocouple) to verify that steel surface temperature is at least 3 °C above the dew point before and throughout blasting and coating. Eliminate salt contamination before blasting using a Bresle patch test — residual chlorides act as hygroscopic nuclei that dramatically accelerate flash rust formation on freshly blasted steel. In unavoidable high-humidity situations, some coating specifications permit application of a blast primer within minutes of blasting, which seals the surface before significant re-oxidation occurs — always check that the blast primer is compatible with the coating system being applied over it.

Yes — significantly. Coarser grits carry more kinetic energy per particle and remove more surface mass per impact event, which translates to faster cleaning rates on contaminated steel. On Grade A (intact mill scale) carbon steel at 80 PSI with a 7 mm bore venturi nozzle, a rough comparison: F16 achieves approximately 8–12 m²/hour; F36 achieves approximately 15–22 m²/hour. The finer grit is faster because it delivers more impact events per second over the blast pattern area, even though each event removes less material. The crossover point depends on the contamination type — for mill scale, which requires aggressive undercutting, F16–F24 is faster per unit of specification-grade area achieved; for light rust (Grade C–D), F36–F46 is faster per unit area because there is no hard scale layer to overcome. Match grit to contamination type, not just to the target profile depth.

For Sa 2½ (SSPC-SP 10) with a minimum 50 µm Rz on mild steel, the standard specification is brown fused aluminum oxide F24–F36 at 70–85 PSI. F36 will typically deliver Rz 40–65 µm on Grade B–C steel — the lower portion of this range may fall just under 50 µm on softer Grade D steel with minimal surface contamination. To ensure you consistently hit 50 µm minimum, order F24 if your steel is Grade A–B (significant mill scale present), or F36 if your steel is Grade B–D with moderate-to-heavy rust and minimal scale. Run a trial blast and measure with Testex replica tape before committing to full production — the combination of your specific steel hardness, blast equipment, and operating conditions will define the achieved Rz more precisely than any table can predict in the abstract.

Source the Right Grade for Your Steel Application

Jiangsu Henglihong Technology supplies brown fused and white fused aluminum oxide abrasives in the full FEPA grit range — with lot-specific Certificates of Analysis, ISO 9001:2015 quality management, and global export capability.

Request a Quote View Products