{
    "slug": "coating-thickness",
    "title": "Coating Thickness vs Salt Spray Hours by Finish",
    "description": "Coating thickness vs salt-spray hours for 13 CNC finishes: anodize, zinc plate, HDG, zinc-flake, phosphate, black oxide, powder and Ni-Cr, endpoints stated.",
    "lang": "en",
    "tables": [
        {
            "caption": "Coating thickness vs corrosion resistance — 13 finishes (NSS per ASTM B117 / ISO 9227)",
            "columns": [
                "Process",
                "Coating thickness (µm)",
                "Salt spray, NSS — endpoint stated",
                "Substrate",
                "Typical application",
                "Cost tier (editorial, 1–5)",
                "Standard",
                "Source"
            ],
            "rows": [
                {
                    "Process": "Anodizing Type II (sulfuric, conventional)",
                    "Coating thickness (µm)": "5–25 (spec window 2–25; decorative Class 2 commonly 8–15)",
                    "Salt spray, NSS — endpoint stated": "336 h, sealed specimens, no corrosion beyond spec limits",
                    "Substrate": "Aluminum alloys",
                    "Typical application": "Enclosures, consumer electronics, trim",
                    "Cost tier (editorial, 1–5)": "3",
                    "Standard": "MIL-PRF-8625F (formerly MIL-A-8625F) Type II",
                    "Source": "S1 / S3 / S4"
                },
                {
                    "Process": "Anodizing Type III (hardcoat)",
                    "Coating thickness (µm)": "25–75 (nominal 50.8 µm / 0.002 in)",
                    "Salt spray, NSS — endpoint stated": "336 h, sealed specimens, no corrosion beyond spec limits",
                    "Substrate": "Aluminum alloys",
                    "Typical application": "Hydraulic bores, wear plates",
                    "Cost tier (editorial, 1–5)": "4",
                    "Standard": "MIL-PRF-8625F Type III; ISO 10074",
                    "Source": "S2 / S3"
                },
                {
                    "Process": "Electroless nickel, mid-phosphorus (Type IV, 5–9% P)",
                    "Coating thickness (µm)": "SC1 5 / SC2 13 / SC3 25 / SC4 75 (minimums)",
                    "Salt spray, NSS — endpoint stated": "Typically 48–96 h to red rust (supplier data; B733 itself sets no NSS hours)",
                    "Substrate": "Steel, aluminum, stainless, copper alloys",
                    "Typical application": "Valve bodies, general industrial parts",
                    "Cost tier (editorial, 1–5)": "4",
                    "Standard": "ASTM B733",
                    "Source": "S5 / S6 / S7"
                },
                {
                    "Process": "Electroless nickel, high-phosphorus (Type V, above 10% P)",
                    "Coating thickness (µm)": "≥25 (SC3 and up; marine commonly 50)",
                    "Salt spray, NSS — endpoint stated": "Typically ≥1,000 h to red rust at 25 µm; up to 2,000 h after diffusion treatment (supplier data)",
                    "Substrate": "Steel, aluminum, copper",
                    "Typical application": "Marine, oil and gas, non-magnetic parts",
                    "Cost tier (editorial, 1–5)": "5",
                    "Standard": "ASTM B733 (high-phosphorus salt-spray clause)",
                    "Source": "S5 / S7 / S8 / S9"
                },
                {
                    "Process": "Zinc electroplate + clear trivalent passivate (Type V)",
                    "Coating thickness (µm)": "SC1 5 / SC2 8 / SC3 12 / SC4 25 (minimums)",
                    "Salt spray, NSS — endpoint stated": "72 h to white rust (Type V)",
                    "Substrate": "Steel",
                    "Typical application": "Indoor and light-duty fasteners and parts",
                    "Cost tier (editorial, 1–5)": "2",
                    "Standard": "ASTM B633",
                    "Source": "S10 / S11 / S12"
                },
                {
                    "Process": "Zinc electroplate + colored passivate (Type II hexavalent / Type VI trivalent)",
                    "Coating thickness (µm)": "SC1 5 / SC2 8 / SC3 12 / SC4 25 (minimums)",
                    "Salt spray, NSS — endpoint stated": "96 h (Type II) / 120 h (Type VI) to white rust",
                    "Substrate": "Steel",
                    "Typical application": "Outdoor-adjacent hardware",
                    "Cost tier (editorial, 1–5)": "2",
                    "Standard": "ASTM B633",
                    "Source": "S10 / S11 / S12"
                },
                {
                    "Process": "Hot-dip galvanizing (HDG)",
                    "Coating thickness (µm)": "45–100 (A123 grade, by steel category and thickness); EN ISO 1461: 85 µm average on steel ≥6 mm",
                    "Salt spray, NSS — endpoint stated": "Not specified by standard — accepted by thickness; typically 500 h+ to red rust (supplier data)",
                    "Substrate": "Steel",
                    "Typical application": "Structural, long-life outdoor",
                    "Cost tier (editorial, 1–5)": "2",
                    "Standard": "ASTM A123 (parts) / A153 (fasteners); EN ISO 1461",
                    "Source": "S14 / S15 / S16 / S26"
                },
                {
                    "Process": "Zinc-flake coating (Dacromet / Geomet type)",
                    "Coating thickness (µm)": "4–10 (sealer plus topcoat, reference)",
                    "Salt spray, NSS — endpoint stated": "240 h at 4 µm / 480 h at 5 / 600 h at 6 / 720 h at 8 / 960 h at 10 µm, no red rust; 72 h no red rust at a scribe (sacrificial)",
                    "Substrate": "Steel (preferred on ≥1,000 MPa high-strength fasteners)",
                    "Typical application": "Automotive chassis bolts; service where hydrogen embrittlement must be ruled out",
                    "Cost tier (editorial, 1–5)": "3",
                    "Standard": "ISO 10683:2018",
                    "Source": "S17 / S18 / S19"
                },
                {
                    "Process": "Zinc phosphate (Type Z) + oil (Class 2)",
                    "Coating thickness (µm)": "2–15",
                    "Salt spray, NSS — endpoint stated": "≥72 h to red rust with the specified oil supplement",
                    "Substrate": "Steel",
                    "Typical application": "Paint and powder pre-treatment, fasteners",
                    "Cost tier (editorial, 1–5)": "1",
                    "Standard": "MIL-DTL-16232G",
                    "Source": "S20 / S21 / S23"
                },
                {
                    "Process": "Manganese phosphate (Type M) + oil (Class 2)",
                    "Coating thickness (µm)": "Heavy film (accepted by coating weight per area, not µm)",
                    "Salt spray, NSS — endpoint stated": "≥48 h to red rust with the specified oil supplement",
                    "Substrate": "Steel",
                    "Typical application": "Gears and sliding parts for run-in and oil retention",
                    "Cost tier (editorial, 1–5)": "1",
                    "Standard": "MIL-DTL-16232G (DFL supplemental system: 100 h clause)",
                    "Source": "S20 / S22 / S23"
                },
                {
                    "Process": "Black oxide + supplementary oil or wax",
                    "Coating thickness (µm)": "0.5–2 (magnetite film ≈0.76 µm)",
                    "Salt spray, NSS — endpoint stated": "24–48 h (S26) / 24–72 h (S24) to red rust — both intervals listed, see the register",
                    "Substrate": "Steel, stainless",
                    "Typical application": "Indoor machinery, appearance, zero dimensional change",
                    "Cost tier (editorial, 1–5)": "1",
                    "Standard": "MIL-DTL-13924",
                    "Source": "S24 / S25 / S26"
                },
                {
                    "Process": "Powder coating (epoxy / polyester / hybrid)",
                    "Coating thickness (µm)": "60–120",
                    "Salt spray, NSS — endpoint stated": "Typically epoxy 1,000+ h / polyester 500–1,000 h / hybrid 500–800 h; acceptance by scribe creepage ≤2–3 mm (ASTM D1654)",
                    "Substrate": "Steel, aluminum",
                    "Typical application": "Enclosures, furniture, architectural",
                    "Cost tier (editorial, 1–5)": "2",
                    "Standard": "Test methods ASTM B117 + D1654/D714 (no single governing spec; QUALICOAT for architectural)",
                    "Source": "S27 / S28 / S29"
                },
                {
                    "Process": "Decorative nickel + chromium (Ni/Cr)",
                    "Coating thickness (µm)": "Ni 10–30 + Cr 0.13–0.8 (DB34 example: Ni ≥20 + Cr ≥0.25)",
                    "Salt spray, NSS — endpoint stated": "NSS 24–96 h depending on system (single-layer 12 µm Ni ≈24 h; copper under-layer + multilayer Ni passes 96 h); acceptance via CASS (ASTM B368), SC4 service condition 22–24 h",
                    "Substrate": "Steel, brass, copper alloys",
                    "Typical application": "Cosmetic hardware, hand tools",
                    "Cost tier (editorial, 1–5)": "4",
                    "Standard": "ASTM B456 / B368",
                    "Source": "S30 / S31"
                }
            ]
        },
        {
            "caption": "My Part Is 6061 Aluminum — Which Coating Survives 500 Hours of Salt Spray?",
            "columns": [
                "Coating (aluminum-eligible)",
                "Thickness (µm)",
                "NSS hours",
                "How to read it"
            ],
            "rows": [
                {
                    "Coating (aluminum-eligible)": "Type II anodize, sealed",
                    "Thickness (µm)": "5–25",
                    "NSS hours": "336 h (spec)",
                    "How to read it": "The appearance default; dimensionally tight"
                },
                {
                    "Coating (aluminum-eligible)": "Type III hardcoat, sealed",
                    "Thickness (µm)": "25–75",
                    "NSS hours": "336 h (spec); typically higher",
                    "How to read it": "Wear plus corrosion in one step"
                },
                {
                    "Coating (aluminum-eligible)": "High-phosphorus electroless nickel",
                    "Thickness (µm)": "≥25",
                    "NSS hours": "≥1,000 h typical (supplier data)",
                    "How to read it": "Uniform in blind holes; the 1,000 h+ pick"
                },
                {
                    "Coating (aluminum-eligible)": "Polyester powder",
                    "Thickness (µm)": "60–120",
                    "NSS hours": "500–1,000 h typical",
                    "How to read it": "Thickest barrier; adds the most dimension"
                }
            ]
        },
        {
            "caption": "How Much Does Hard Anodizing Add to My Part Dimensions?",
            "columns": [
                "Case",
                "Thickness (µm)",
                "Growth per face (µm)",
                "Across a coated diameter (µm)"
            ],
            "rows": [
                {
                    "Case": "Type III at nominal 50 (spec 50.8 µm / 0.002 in)",
                    "Thickness (µm)": "50",
                    "Growth per face (µm)": "≈25",
                    "Across a coated diameter (µm)": "≈50"
                },
                {
                    "Case": "Type II at the 8–15 mid-band (12 µm, calculated)",
                    "Thickness (µm)": "12",
                    "Growth per face (µm)": "≈6",
                    "Across a coated diameter (µm)": "≈12"
                }
            ]
        },
        {
            "caption": "What Zinc Plating Thickness Do I Need Outdoors?",
            "columns": [
                "Service condition",
                "Minimum zinc (µm)",
                "Typical environment",
                "Type V clear (h to white rust)",
                "Type II colored (h to white rust)",
                "Type VI colored (h to white rust)"
            ],
            "rows": [
                {
                    "Service condition": "SC1",
                    "Minimum zinc (µm)": "5",
                    "Typical environment": "Indoor, dry",
                    "Type V clear (h to white rust)": "72",
                    "Type II colored (h to white rust)": "96",
                    "Type VI colored (h to white rust)": "120"
                },
                {
                    "Service condition": "SC2",
                    "Minimum zinc (µm)": "8",
                    "Typical environment": "Indoor humidity, light exposure",
                    "Type V clear (h to white rust)": "72",
                    "Type II colored (h to white rust)": "96",
                    "Type VI colored (h to white rust)": "120"
                },
                {
                    "Service condition": "SC3",
                    "Minimum zinc (µm)": "12",
                    "Typical environment": "Occasional rain and condensation",
                    "Type V clear (h to white rust)": "72",
                    "Type II colored (h to white rust)": "96",
                    "Type VI colored (h to white rust)": "120"
                },
                {
                    "Service condition": "SC4",
                    "Minimum zinc (µm)": "25",
                    "Typical environment": "Saline or frequently wet",
                    "Type V clear (h to white rust)": "72",
                    "Type II colored (h to white rust)": "96",
                    "Type VI colored (h to white rust)": "120"
                }
            ]
        },
        {
            "caption": "Blue-White Zinc or Yellow Zinc — Which Lasts Longer?",
            "columns": [
                "Passivate type",
                "Chemistry",
                "To white rust"
            ],
            "rows": [
                {
                    "Passivate type": "Type V",
                    "Chemistry": "Clear trivalent passivate (blue-white)",
                    "To white rust": "72 h"
                },
                {
                    "Passivate type": "Type II",
                    "Chemistry": "Colored chromate, hexavalent (yellow)",
                    "To white rust": "96 h"
                },
                {
                    "Passivate type": "Type VI",
                    "Chemistry": "Colored passivate, trivalent",
                    "To white rust": "120 h"
                }
            ]
        },
        {
            "caption": "Why Specify Zinc-Flake Coating on 12.9-Class Bolts?",
            "columns": [
                "Coating thickness (µm)",
                "NSS to first red rust (h)"
            ],
            "rows": [
                {
                    "Coating thickness (µm)": "4",
                    "NSS to first red rust (h)": "240"
                },
                {
                    "Coating thickness (µm)": "5",
                    "NSS to first red rust (h)": "480"
                },
                {
                    "Coating thickness (µm)": "6",
                    "NSS to first red rust (h)": "600"
                },
                {
                    "Coating thickness (µm)": "8",
                    "NSS to first red rust (h)": "720"
                },
                {
                    "Coating thickness (µm)": "10",
                    "NSS to first red rust (h)": "960"
                }
            ]
        },
        {
            "caption": "Does Hot-Dip Galvanizing Need a Salt Spray Certificate?",
            "columns": [
                "Standard",
                "Scope",
                "Acceptance basis",
                "Coating thickness"
            ],
            "rows": [
                {
                    "Standard": "ASTM A123",
                    "Scope": "Articles and assemblies after fabrication",
                    "Acceptance basis": "Coating grade by steel category and thickness",
                    "Coating thickness": "45–100 µm average"
                },
                {
                    "Standard": "ASTM A153",
                    "Scope": "Fasteners and hardware",
                    "Acceptance basis": "Coating class",
                    "Coating thickness": "Per class; not tabulated on this page"
                },
                {
                    "Standard": "EN ISO 1461",
                    "Scope": "After-fabrication galvanizing",
                    "Acceptance basis": "Average minimum by steel thickness",
                    "Coating thickness": "85 µm average on steel ≥6 mm"
                }
            ]
        },
        {
            "caption": "Can Electroless Nickel Pass 1,000 Hours?",
            "columns": [
                "Type",
                "Thickness classes",
                "Typical NSS",
                "Typical use"
            ],
            "rows": [
                {
                    "Type": "Type IV, mid-P (5–9% P)",
                    "Thickness classes": "SC1 5 / SC2 13 / SC3 25 / SC4 75 µm minimums",
                    "Typical NSS": "48–96 h to red rust",
                    "Typical use": "Valve bodies, general industrial"
                },
                {
                    "Type": "Type V, high-P (above 10% P)",
                    "Thickness classes": "≥25 µm (SC3 and up); marine commonly 50 µm",
                    "Typical NSS": "≥1,000 h to red rust; up to 2,000 h after diffusion",
                    "Typical use": "Marine, oil and gas, non-magnetic parts"
                }
            ]
        },
        {
            "caption": "Is Black Oxide Enough for Outdoor Parts?",
            "columns": [
                "Process",
                "Film",
                "NSS with supplement",
                "Supplement"
            ],
            "rows": [
                {
                    "Process": "Black oxide (MIL-DTL-13924)",
                    "Film": "0.5–2 µm (≈0.76 µm magnetite)",
                    "NSS with supplement": "24–48 h (S26) / 24–72 h (S24) to red rust",
                    "Supplement": "Oil or wax required"
                },
                {
                    "Process": "Zinc phosphate, Type Z (MIL-DTL-16232G)",
                    "Film": "2–15 µm",
                    "NSS with supplement": "≥72 h to red rust",
                    "Supplement": "Specified oil, Class 2"
                },
                {
                    "Process": "Manganese phosphate, Type M (MIL-DTL-16232G)",
                    "Film": "Heavy film, accepted by coating weight",
                    "NSS with supplement": "≥48 h to red rust; DFL supplemental system 100 h",
                    "Supplement": "Specified oil, Class 2"
                }
            ]
        },
        {
            "caption": "Powder Coat or Anodize for an Outdoor Aluminium Enclosure?",
            "columns": [
                "Resin family",
                "Thickness (µm)",
                "Typical NSS",
                "Note"
            ],
            "rows": [
                {
                    "Resin family": "Epoxy",
                    "Thickness (µm)": "60–120",
                    "Typical NSS": "1,000+ h",
                    "Note": "Highest hours of the three families"
                },
                {
                    "Resin family": "Polyester",
                    "Thickness (µm)": "60–120",
                    "Typical NSS": "500–1,000 h",
                    "Note": "The common outdoor choice"
                },
                {
                    "Resin family": "Hybrid (epoxy-polyester)",
                    "Thickness (µm)": "60–120",
                    "Typical NSS": "500–800 h",
                    "Note": "Balance of the two"
                }
            ]
        },
        {
            "caption": "How Much Nickel Is Required Under Decorative Chrome?",
            "columns": [
                "Conflict point",
                "Source A",
                "Source B",
                "Handling on this page"
            ],
            "rows": [
                {
                    "Conflict point": "Black oxide + oil salt-spray interval",
                    "Source A": "24–48 h (S26)",
                    "Source B": "24–72 h (S24)",
                    "Handling on this page": "Both intervals listed in the main table; size from the conservative 24 h"
                },
                {
                    "Conflict point": "ASTM B633 salt-spray hours",
                    "Source A": "Type II 96 h / Type V 72 h / Type VI 120 h to white rust (S10, S11, S12 agree)",
                    "Source B": "Type I 48 h / Type II 240 h to red rust (S13, single source)",
                    "Handling on this page": "Table uses the three-source set; S13 is quarantined here, not in the tables"
                },
                {
                    "Conflict point": "Zinc SC3 thickness",
                    "Source A": "12 µm (S10, S11, S12)",
                    "Source B": "13 µm (S15, rounding of 0.0005 in)",
                    "Handling on this page": "Table pins 12 µm; the rounding is noted in the footnotes"
                },
                {
                    "Conflict point": "Type II anodize salt spray",
                    "Source A": "Sealed 336 h per MIL-PRF-8625F (S1, S3, S4)",
                    "Source B": "Up to 168 h (low-authority SEO page)",
                    "Handling on this page": "336 h per the specification; the SEO figure is dropped"
                },
                {
                    "Conflict point": "HDG salt-spray hours",
                    "Source A": "Not specified by the standard — accepted by thickness grade (S14, S15, S16)",
                    "Source B": "500 h+ to red rust (S26, supplier data)",
                    "Handling on this page": "Table states standard-silent; the typical value is listed separately"
                }
            ]
        }
    ]
}