TECHNICAL GUIDE / 2026-10-02
Short answer. A surface can have an acceptable anchor profile and still be unsuitable for coating because dust, salts, oil or other residue remains. Define each acceptance method from the coating specification, clean and inspect at the right time, and record abrasive grade, equipment and substrate history. The brown fused alumina designation alone cannot certify the prepared surface.
Separate cleanliness from profile
Blasting with brown fused alumina can remove a layer and create surface texture, but those are only parts of a coating preparation decision. A coating system may also require limits on dust, soluble salts, oil, residual coating or embedded foreign material. Define the complete inspection checklist from the project specification before work begins. A rough-looking surface is not automatically clean, and a clean-looking surface may lack the required anchor profile. Keep the acceptance criteria and methods distinct so a passing check does not mask a failure elsewhere.
The substrate's history matters. Parts exposed to marine environments, process chemicals or handling oils can bring contaminants that blasting alone may not remove or may spread. Record the pre-cleaning step and any wash, degrease or rinse procedure. If wet blasting is used, water quality and drying become part of the sequence. Do not attribute all post-blast residue to the abrasive without investigating the substrate and process inputs.
Inspect airborne and settled dust
Dust can originate from broken abrasive, the old coating, rust, scale or substrate. The site's approved dust test should be performed after the specified cleaning step and before coating, with representative locations. A quick hand wipe may reveal a concern but does not replace an agreed method. Record whether compressed air, vacuuming or another approved cleaning route was used. Also check recesses and edges where material can settle after a broad flat area appears clean.
If a new abrasive supplier is being evaluated, compare the fresh media's documented grade and lot with the actual circulating or reclaimed media. Fines accumulated in a blast system can influence dust left on the surface. Check extraction and separator condition before declaring a grain problem. A change in nozzle pressure or stand-off can also alter the amount of fractured material. Keep equipment settings and reclaim history with the surface inspection record.
Check soluble or oily residue by the specified method
Where a coating specification requires soluble-salt testing, follow its named sampling and analytical method. The acceptable value and interpretation belong to the coating or project technical owner, not to a generic abrasive seller. Sampling time and location matter: rain, cleaning water, handling or a delay after blasting can change the surface. Record the method, result and any corrective wash and retest. A successful profile measurement does not waive the chemical cleanliness requirement.
Oil or grease may be present before blasting and can be driven into or spread across the surface. Pre-cleaning should address it under the approved process. After blasting, inspect for residues by the specified visual or test method. If the source appears to be the compressed-air system or handling equipment, repair that cause before changing abrasive grades. A supplier PDS for brown fused alumina does not certify that the customer's air line, wash water or gloves are clean.
Control the interval before coating
Prepared surfaces can be recontaminated during waiting, transport or handling. Set an approved time window and environmental conditions for inspection and coating. If the window is exceeded or the surface is exposed, apply the project's reinspection rule. Keep the workpiece ID, inspection time, abrasive batch, blast settings and coating application time together. This trail helps distinguish an abrasive issue from contamination that entered after the blast operation was finished.
When a check fails, isolate the affected area or parts and follow the approved cleaning and retest procedure. Do not simply blast longer without considering profile, substrate loss or the actual contaminant. A targeted response may involve re-cleaning, water treatment, equipment repair or media replacement. Use measured evidence to choose the step and document the final passing condition before coating.
Selection guidance
For CHAOYAN, state the substrate, existing contamination, coating system, intended F grit, fresh or reclaimed media use, and the specified surface checks. Request the exact abrasive product sheet and sample for a controlled trial. The surface-preparation guide covers the process; the anchor-profile guide addresses texture measurement. This article addresses contamination that may remain after a seemingly successful blast. The coating decision belongs to the full inspection record, not one abrasive characteristic or photograph.
Common mistakes
- Treating an acceptable profile as proof that salts and dust are absent.
- Blaming the abrasive for contamination from a substrate, air line or rinse water.
- Inspecting a flat test area while ignoring edges and recesses.
- Coating after an uncontrolled delay without rechecking the surface.
Related technical guidance
Frequently asked questions
Does using brown fused alumina eliminate soluble-salt testing?
No. If the coating specification requires that test, perform it on the prepared surface by the named method regardless of abrasive choice.
Can a clean-looking surface still fail coating preparation?
Yes. Dust, salts, oil or an out-of-range profile may not be reliably judged by appearance alone. Use the approved inspection plan.
