CategoryShot Blasting
Shot blasting for steel: cleanliness grades, surface roughness and what a quote needs
Shot blasting propels abrasive at the steel surface to strip mill scale, rust and old coatings, leaving a clean, uniformly roughened profile that primer and coatings key into. This page covers what actually decides the outcome — the cleanliness grade a standard defines against what a supplier will commit to, the surface roughness the process leaves, and the six things a shop needs before it can quote a firm price instead of a range. Where the industry publishes no figure, this page says so rather than filling the gap.
Cleanliness grades
Sa 1
Equivalent: SSPC-SP7 / NACE No. 4
Light blast cleaning. Loose mill scale, rust and old coatings are removed; firmly adhering residues may remain.
Standard-defined
Source: ISO 8501-1 — light blast-cleaning grade Sa 1 (worldofcorrosion.com grade summary; SSPC/NACE cross-reference independently confirmed via Belzona and HLH cross-reference pages)
Sa 2
Equivalent: SSPC-SP6 / NACE No. 3
Thorough blast cleaning. Most mill scale, rust and old coatings are removed; slight residual shadows and stains are permitted.
Standard-defined
Source: ISO 8501-1 — thorough blast-cleaning grade Sa 2
Sa 2½
Equivalent: SSPC-SP10 / NACE No. 2
Very thorough (near-white) blast cleaning. The surface is free of visible mill scale, rust and old coatings except for slight shadows or stains — the grade most steel stockholders offer as standard.
Standard-defined
Source: ISO 8501-1 — near-white blast-cleaning grade Sa 2½; confirmed as an actually-stocked service by Stahlhandel Ulm ('Strahlen SA 2,5')
Sa 3
Equivalent: SSPC-SP5 / NACE No. 1
White metal blast cleaning. Uniform metallic appearance, with no visible mill scale, rust, old coatings or other contaminants.
Standard-defined
Source: ISO 8501-1 — white metal blast-cleaning grade Sa 3
Surface roughness
| Grade | Roughness (Ra) | | |
|---|
| Fine | 23–28 µm | Standard-defined | Source: ISO 8503-1/-2, shot-blasting (Type S) comparator segment, as published by messmittel.tools |
|---|
| Medium | 35–45 µm | Standard-defined | Source: ISO 8503-1/-2, shot-blasting (Type S) comparator segment, as published by messmittel.tools |
|---|
| Coarse | 60–80 µm | Standard-defined | Source: ISO 8503-1/-2, shot-blasting (Type S) comparator segment, as published by messmittel.tools |
|---|
Indicative figures published by standards and suppliers, not a quotation. Confirm the achievable grade and roughness with the provider for your material, its condition and the quantity.
What drives the price
- Abrasive media and target grade
- Starting surface condition — mill scale, rust grade, old coating
- Part size and total surface area
- Batch size
- Access — single side, both sides, or fully enclosed shapes
What a quote needs
- The material and its current surface condition
- The target cleanliness grade you need
- Part dimensions and quantity
- The total surface area to be blasted
- Any areas that must be masked off
- Delivery address and the date you need it
Traceability and EN 10204 certificates
Standard for steel purchases: 3.1
Blasting does not itself create an EN 10204 certificate — the certificate belongs to the material. The real question is whether traceability survives the blast and how each part is re-marked so it does.
Standard-defined
Source: EN 10204 defines inspection-document types; Holter Eisenhandel explicitly offers 'Werkszeugnis 2.2 oder ein Abnahmeprüfzeugnis 3.1' as part of its Anarbeitung programme.
Services
What cleanliness grades does shot blasting achieve?
Shot blasting is specified against ISO 8501-1, which defines cleanliness grades by how completely mill scale, rust and old coatings are removed. Sa 1 (light blast cleaning) removes loose scale and rust while firmly adhering residue may remain — equivalent to SSPC-SP7 / NACE No. 4. Sa 2 (thorough blast cleaning) removes most contamination with slight staining permitted — SSPC-SP6 / NACE No. 3. Sa 2½ (near-white, very thorough) leaves only slight shadows or stains — SSPC-SP10 / NACE No. 2, and the grade most steel stockholders offer as their standard service. Sa 3 (white metal) leaves a uniform metallic appearance with no visible contamination at all — SSPC-SP5 / NACE No. 1.
Sa 2½ or Sa 3 — which one do I need?
Sa 2½ is the practical standard for most coating systems: near-white, with only slight shadows or stains permitted, and it is what steel stockholders typically stock as their default blasting service. Sa 3 (white metal) removes every visible trace of contamination and is reserved for the most demanding coating or corrosion-protection specifications, where the cost of the extra blasting time is justified by the service the steel will see. Unless your coating specification or project standard explicitly calls for Sa 3, Sa 2½ is usually the right and more economical choice — confirm the requirement against your coating manufacturer's data sheet or your project specification.
How rough is the surface after shot blasting?
ISO 8503 grades the surface profile separately from the cleanliness grade, using a comparator with Fine, Medium and Coarse segments. For shot blasting (dimpled profile, Type S), published figures are Fine 23–28 µm, Medium 35–45 µm and Coarse 60–80 µm, measured as Ra. Which band you land in depends on the abrasive size and blasting parameters used, not on the Sa cleanliness grade — a Sa 2½ surface can be blasted to a fine or a coarse profile depending on what the coating that follows needs. State the roughness band your coating system requires alongside the cleanliness grade when you order.
What abrasive media do you use?
ISO 8503 distinguishes surfaces by the profile shape the abrasive leaves rather than by a specific product: shot abrasive (Type S) leaves a dimpled profile, grit abrasive (Type G) leaves an angular one, and the roughness figures on this page are for the shot (Type S) profile specifically. None of the suppliers we reviewed publish the specific media — steel shot size, grit type or brand — that they run, so we will not invent one. Ask the provider directly which abrasive they use and whether it matches the profile shape your coating specification calls for.
What size parts can you blast?
It depends on the shop's equipment. One supplier's continuous-line system runs a pass-through opening of 1500 x 500 mm at a throughput of 0.8–1.5 m/min, descaling all sides; another runs a batch system that accommodates plate up to 124 in wide with a maximum height of 14 in. Both figures describe one supplier's machine, not an industry limit — a shop with a larger chamber or a wider continuous line handles larger parts. Confirm your part's dimensions against the specific shop's equipment before ordering.
Do I get an EN 10204 certificate?
The same answer as for any processed steel: blasting does not create a certificate. EN 10204 defines the inspection-document types 2.1, 2.2, 3.1 and 3.2; one supplier in this lane explicitly offers 'Werkszeugnis 2.2 or an Abnahmeprüfzeugnis 3.1' as part of its processing programme, and 3.1 is the usual default in steel procurement. What matters is whether traceability survives the blast and how each part is re-marked so the heat or batch stays linked to it. Ask the provider directly how they handle re-marking.
What does shot blasting cost?
Shot blasting is not priced from a single rate, so any figure quoted here would mislead. What drives it is the abrasive and the target cleanliness grade, the starting surface condition — how much mill scale, rust or old coating has to come off — the part size and total surface area, the batch size, and whether the shop needs to reach both sides or the inside of an enclosed shape. Send the six items in the quote checklist and you will get a firm price instead of a range.
What information do you need for a quote?
The material and its current surface condition, the target cleanliness grade you need, part dimensions and quantity, the total surface area to be blasted, any areas that must be masked off, and the delivery address with the date. Those six turn an enquiry into a firm price rather than a range.
Is there a minimum order quantity?
There is no industry-wide minimum order quantity for shot blasting; it varies by provider. Some shops blast single parts as part of a larger processing order, others set a practical minimum batch. Ask as part of your enquiry rather than assuming.
What is the lead time?
No supplier in the sources we reviewed publishes a standard lead time for shot blasting, and we will not invent one. It depends on the shop's queue, the batch size and whether the part needs other processing first. Ask the provider directly when you enquire.
Why blast steel before welding or cutting?
A blasted surface removes mill scale, rust and old coatings that would otherwise interfere with downstream work: robotic welding sees a clean, consistent surface to arc against, and laser cutting starts from bare metal instead of a scaled one, both of which improve process reliability. It is also the standard first step before priming or coating, since paint keys into the roughened profile a blast leaves rather than a smooth mill surface. Shipbuilding, railcar manufacturing and structural fabrication all use it as a preparation step ahead of welding, cutting or coating.
Can you blast the inside of pipes and profiles, not just the outside?
Yes — one supplier in this lane specifically advertises mechanical descaling and blasting for both internal and external surfaces, which matters for tube, pipe and hollow profile work where the bore needs the same cleanliness grade as the outside. Confirm with the provider that their equipment reaches the specific internal diameter and length of your part, since internal access is a function of their equipment, not a given for every shop.
