Specialist · 10 checks

Protective Coatings
QA inspection checklist

Industrial protective coatings and specialist painting quality audit.

Every check below carries what good looks like, when it passes, the standard it comes from and the defects that usually fail it. That guidance is what turns a tick-box into an inspection.

Surface Preparation

  1. 1.
    Blast cleaning to specified standard (Sa2.5/Sa3)
    What to look forSurface visually inspected against ISO 8501-1 photographic standards. Sa 2.5 ("very thorough blast cleaning") shows only slight staining of mill scale, rust, and old paint. Sa 3 ("blast cleaning to visually clean steel") fully white-metal. Compared against ISO printed reference.
    Acceptable whenPer ISO 8501-1:2007 / NORSOK M-501: surface preparation per coating system spec — typical Sa 2.5 for atmospheric, Sa 3 for immersed / aggressive. Verified against ISO photographic standard.
    StandardISO 8501-1:2007 — Surface preparation visual assessment. ISO 12944-4 (preparation methods). NORSOK M-501.
    Common defectsSa 2 only achieved when Sa 2.5 specified — coating life shortenedMill scale residue at cornersFlash rust between blast and coat (re-blast required)Old paint not fully removedNo photographic record of preparation
  2. 2.
    Surface profile within specification
    Record: Profile (μm)
    What to look forSurface profile (peak-to-valley height) measured with replica tape (Testex / Press-O-Film) or digital surface profile gauge. Sample multiple areas. Profile depth per coating manufacturer / spec.
    Acceptable whenPer ISO 8503 / coating ETA: profile depth per coat — typical 50-75 µm (medium G-grade) for primers; 75-100 µm (coarse / G/H) for thick film systems. Measured with replica tape per ISO 8503-5.
    StandardISO 8503-1/2/3/4/5:2012 — Roughness characteristics of blast-cleaned surfaces.
    Common defectsProfile too shallow — poor mechanical key, peelingProfile too deep — coating cannot fill peaks, holidaysProfile measured at one spot — local variations missedWorn shot reused — round particles, low profileNo replica tape readings recorded
  3. 3.
    Dust level acceptable
    What to look forDust level checked by adhesive tape lift (ISO 8502-3) at sample points. Class 1-2 (low) acceptable for most coating systems. Surface vacuumed / blown clean. No abrasive grit residue. Surface chloride / soluble salt below threshold.
    Acceptable whenPer ISO 8502-3:2017 / ISO 8502-6 (chloride): dust class ≤ 2 typical; soluble chloride < 30 mg/m² for atmospheric, < 20 mg/m² for immersed.
    StandardISO 8502-3:2017 — Assessment of dust on prepared surfaces. ISO 8502-6 — Chloride. ISO 8502-9 (Bresle method).
    Common defectsDust class > 3 — coating bond failsSoluble salts > 30 mg/m² — osmotic blisteringBresle test not performedSurface contaminated by adjacent worksTape test not performed at sample density
  4. 4.
    Surface temperature and dewpoint checked
    Record: Temp / RH
    What to look forSurface temperature ≥ 3°C above dewpoint at time of coating. Air temperature, RH, surface temp logged hourly during application. No coating in rain, mist, or condensation. Wet-bulb data recorded.
    Acceptable whenPer ISO 12944-7 / coating manufacturer / NORSOK M-501: surface temperature ≥ dewpoint + 3°C (or as TDS); RH ≤ 85% (or as TDS); ambient ≥ minimum for product (typically ≥ 5°C for paint, ≥ 10°C for some).
    StandardISO 12944-7:2017 — Execution and supervision of paint work. NORSOK M-501. Manufacturer TDS.
    Common defectsSurface within 3°C of dewpoint — moisture on surface, blisteringNo environmental log — non-compliantCoating applied in rain — contaminationBelow product minimum temperature — slow / incomplete cureRH > 85% — moisture absorption

Coating Application

  1. 5.
    Coating system matches specification (primer/intermediate/topcoat)
    What to look forEach coat as designed — primer (zinc-rich, epoxy phenolic, etc.), intermediate (epoxy, MIO), topcoat (PU, fluoropolymer, polysiloxane). Manufacturer batch numbers recorded. Mixing per TDS — correct ratio, induction time observed.
    Acceptable whenPer ISO 12944 / NORSOK M-501 / project spec: system per environment class (C2-C5, Im1-Im4, CX). Each coat per TDS — including mix ratio, pot life, induction time.
    StandardISO 12944-5:2019 — Protective paint systems. NORSOK M-501. Manufacturer TDS.
    Common defectsWrong system grade (C3 used in C5-M environment)Coat omitted from systemGeneric / cheap product substituted for specifiedMix ratio wrong — incomplete cureInduction time not observed
  2. 6.
    WFT checked during application
    Record: WFT (μm)
    What to look forWet film thickness (WFT) measured during application with WFT comb gauge. WFT = target DFT / volume solids ratio. Operator monitors and adjusts coverage. Multiple readings per area.
    Acceptable whenPer ISO 12944-7 / TDS: WFT calculated from required DFT and product volume solids; WFT measured every few square metres during application. Adjustment to maintain target DFT.
    StandardISO 12944-7:2017. ISO 2808 (DFT measurement). Manufacturer TDS.
    Common defectsWFT not measured — DFT will be off-specOperator not converting DFT to WFT correctlySingle comb reading per area — variation missedComb scratching wet paintNo WFT log
  3. 7.
    DFT within specification per coat
    Record: DFT (μm)
    What to look forDFT measured per coat after cure with calibrated electromagnetic gauge. Multiple readings per area per BS EN ISO 19840 / 90/10 rule. Total system DFT meets spec. Edges / corners verified (Faraday cage areas).
    Acceptable whenPer BS EN ISO 19840:2012: DFT measured at minimum frequency per area; minimum 80% of readings ≥ NDFT (Nominal DFT); none < 80% of NDFT. Maximum 3× NDFT (some specs).
    StandardBS EN ISO 19840:2012 — Measurement of and acceptance criteria for the thickness of dry films. ISO 2808.
    Common defectsDFT below NDFT — corrosion protection halvedDFT excessive (> 3× NDFT) — solvent retention, blisteringEdges thin — early failure at cornersNo DFT recordsGauge not calibrated for substrate
  4. 8.
    Overcoat intervals within product limits
    What to look forTime between coats within minimum (cure time) and maximum (re-coat window) per TDS. Records show times and ambient conditions. If maximum exceeded, surface re-prepared per TDS (de-glossed, re-blasted, etc.).
    Acceptable whenPer ISO 12944-7 / manufacturer TDS: overcoat window per product, depending on temperature. If exceeded, re-preparation per TDS instructions. Record of times and conditions.
    StandardISO 12944-7:2017. Manufacturer TDS.
    Common defectsRe-coat window exceeded — bond fails between coatsCoat applied before cure — solvent entrapmentNo record of timesRe-preparation skipped after window exceededHigh-build coat over fresh coat — cracking
  5. 9.
    No runs, sags, misses, or contamination
    What to look forVisual inspection of cured film. No runs, sags, dust contamination, fish-eyes, orange peel, dry-spray, or holidays. Film smooth and uniform. Colour matches sample.
    Acceptable whenPer ISO 12944-7 / SSPC-PA 1: film free from defects that compromise durability. Cosmetic defects per project spec — Class A (top quality) or B per environment.
    StandardISO 12944-7:2017. SSPC-PA 1 — Shop, field, and maintenance painting of steel.
    Common defectsRuns / sags — over-applicationDry spray on adjacent area — poor adhesionDust nibs — windborne contaminationFish-eyes — silicone contaminationHolidays / misses — coating gap
  6. 10.
    Holiday/pinhole detection completed (if required)
    What to look forHoliday detector (low-voltage wet sponge for thin films < 500 µm; high-voltage spark for thicker / immersed) tests entire coated surface. Defects marked, repaired, and re-tested.
    Acceptable whenPer NACE SP0188 / ISO 29601: low-voltage 67.5 V or per coating thickness; high-voltage 5 V/µm typical. 100% coverage on immersed and severe-service coatings. Defects repaired and re-tested.
    StandardNACE SP0188 — Discontinuity testing of new protective coatings. ISO 29601:2011 — Pinhole detection.
    Common defectsHoliday testing skipped on immersed surfaceTest voltage too low — pinholes missedRepairs not re-testedNo record of testSponge wet contaminating coating

Questions people ask

What is a protective coatings QA inspection for?

To record that the work was checked against the specification before it was covered up or handed over: a pass or fail against each item, a measurement where one matters, and a photo where it failed. It is the evidence a client's quantity surveyor or clerk of works asks for, and the thing that settles the argument at final account.

What standards does this checklist check against?

Each item names its reference. On this checklist that includes ISO 8501-1:2007, ISO 8503-1/2/3/4/5:2012, ISO 8502-3:2017, ISO 12944-7:2017, ISO 12944-5:2019, ISO 12944-7:2017. ISO 2808 (DFT measurement). Manufacturer TDS.. The contract specification and the approved drawings always take precedence over a general standard; where they say something stricter, inspect to that.

Who signs a QA inspection off?

The person who carried out the check, named and dated, and where the contract calls for it the client's representative as a witness. The signature records that the check was done and what was found. It is not a warranty of the work.

How many items are on it, and do I have to use them all?

10 checks across 2 sections. Delete what does not apply to the job and add anything the specification asks for that is not here. A checklist that has plainly been thought about carries more weight than a long one nobody read.

Is this useful for a subcontractor as well as a main contractor?

More so. The subcontractor is the one who gets asked to come back and open something up. A signed inspection sheet with photos at the time is the cheapest insurance on a construction site.

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