Description
VpCI®-373 is a water-based wash primer that bonds subsequent primers and topcoats to a range of metals. Cortec specifies it under VpCI-395 on aluminum, galvanized and plated substrates. Thin coat — half a mil to one mil dry. This listing is the green grade in a 5-gallon pail, which covers roughly 5,000 sq ft at the recommended half-mil film.
VpCI-373 replaces the phosphate and chromate conversion treatments that used to be the only way to get paint to stick to aluminum, galvanized steel and plated parts, and it conforms to MIL-P-15328D when used as a bonding primer. Cortec’s application guides for VpCI-395, VpCI-396, VpCI-386, VpCI-375 and VpCI-371 all call for it at 0.5 to 1.0 mil on those substrates, with an adhesion test before full-scale work. It is not a stand-alone finish — Cortec lists only 72 hours salt spray and 100 hours humidity for the primer by itself; its job is adhesion and a first layer of inhibitor under the coating that does the protecting. In the Cortec Product Consultation Guide it is rated 3 (outside, sheltered) on carbon steel, stainless steel, cast iron, aluminum, galvanized steel, copper, brass and solder, which describes what the primed-but-uncoated part can tolerate before topcoating.
Typical applications
- Wash primer under VpCI-386 and other topcoats
- Adhesion promoter on multiple metal substrates
- Pre-treatment prior to topcoating
- Aluminum, galvanized and plated parts going under VpCI-395, 396, 375 or 371
- Replacement for phosphate and chromate pretreatment on paint lines
- Bonding primer where MIL-P-15328D is specified
- OEM production lines finishing mixed-metal assemblies
How to apply VpCI-373
- Surface preparation. The substrate must be free of grease, oil, dirt, fingerprints, drawing compounds, rust inhibitors and anything else that would affect adhesion. Cortec recommends VpCI-440 or a similar phosphatizing pretreatment on production lines and a minimum of NACE No. 3 / SSPC-SP6 commercial blast on structural steel. Aluminum and galvanized surfaces must be free of oxide bloom and oil; a clean solvent wipe or alkaline wash and rinse is usually enough.
- Mixing and dilution. Power-agitate to a uniform consistency with a squirrel-cage or drill mixer. VpCI-373 may be thinned with water up to 10 % by volume to adjust viscosity.
- Conditions. Apply between 45 and 90 °F (7 to 32 °C) with the surface at least 5 °F (2 °C) above the dew point. Flash point is 130 °F (54 °C), so treat it as a combustible liquid despite the water base.
- Equipment. Spray, roll, brush or dip. HVLP or conventional spray: 0.009 to 0.021 in tip, 45 to 55 psi air and 10 psi fluid, 3/8 in ID fluid hose no longer than 50 ft, dual-regulated pot kept at gun height. Airless or air-assisted airless: 0.015 to 0.035 in tip, 1,800 to 2,500 psi, 3/8 in ID hose (a 1/4 in whip end is fine) no longer than 100 ft. Tip size depends on pressure and viscosity. A fine tip and low fluid pressure help hold the thin film.
- Film build. Apply 0.5 to 1.0 mil (12.5 to 25 µm) dry, 1.6 to 3.3 mils wet. Theoretical coverage is 495 sq ft per gallon at 1.0 mil DFT, so about 990 sq ft per gallon at 0.5 mil. More is not better; a wash primer works as a thin tie coat.
- Drying and topcoating. Dry to touch in about 20 minutes and dry to handle in about 40 minutes; force-dry 15 to 20 minutes at 150 °F (65 °C) if needed. Apply the topcoat between 40 minutes and 72 hours; after 72 hours scuff-sand before coating. Test adhesion of the full system on a sample before production.
- Cleanup. Clean tools with water while wet; once dry use butyl cellosolve or MEK, following the solvent manufacturer’s safety directions.
- Storage. Keep the container sealed, do not let it freeze and do not store above 100 °F (38 °C). Shelf life is 12 months at 75 °F.
- See the Cortec coatings application guides and comparison table for the shared spray, prep and storage instructions across the Cortec coating range.
Where it fits in the Cortec line
VpCI-373 comes in clear and green; the green grade shows coverage on bright metal. It sits under the permanent coatings: VpCI-386 water-based acrylic topcoat, VpCI-375 one-coat acrylic, VpCI-395 two-component epoxy primer, VpCI-396 moisture-cure urethane and VpCI-371 high-temperature silicone. It is not needed under Cortec’s temporary coatings (VpCI-368, VpCI-369, VpCI-389, VpCI-391) or under CorrVerter, which goes on rusted ferrous steel only. On steel, VpCI-440 phosphatizing pretreatment is the production-line partner. Browse the full Cortec VpCI line.
Field notes
Cortec lists VpCI-373 with VpCI-375, VpCI-386 and VpCI-396 among the coatings used in nuclear power plant maintenance programs, where wash-primed aluminum and galvanized components are topcoated with the same water-based system as the steel (Cortec field data).
Specifications
| Recommended DFT | 0.5–1.0 mil (12.5–25 microns) |
|---|---|
| Coverage | 495 ft²/gal @ 1.0 mil DFT (12.1 m²/L @ 25 µm) |
| VOC (ASTM D3960) | 0.6 lbs/gal (72 g/L) |
| Cleanup | Water |
| Shelf life | 12 months @ 75°F |
| Note | Designed to be topcoated; as a stand-alone film Cortec lists 72 hours salt spray (ASTM B117) and 100 hours humidity (ASTM D1748) |
| Type | Water-based wash primer / adhesion promoter |
| Color | Olive green |
| Specification | Commercial equivalent to MIL-P-15328D; NSN 8010-01-470-2739 |
| Volume solids | 30.9% |
| Gloss (ASTM D523) | 15–25 |
| Pencil hardness (ASTM D3363) | HB; adhesion 5B (ASTM D3359) |
| Recommended WFT | 1.6–3.3 mils (40–83 µm) |
| Viscosity | 18–45 s Zahn #3 |
| Weight per gallon | 10.17 lb (1.22 kg/L) |
| Flash point | 130 °F (54 °C) |
| Dilution | Water, up to 10% by volume |
| Dry to touch / dry to handle | 20 min / 40 min |
| Recoat / topcoat window | 40 min – 72 hr; sand thereafter |
| Force dry | 15–20 min at 150 °F (65 °C) |
| Full cure | 3–7 days |
| Substrates | Aluminum, galvanized steel and plated parts under Cortec coatings; also carbon steel, stainless steel, cast iron |
| Consultation guide rating | 3 – outside, sheltered (before topcoating) |
| Application temperature | 45–90 °F (7–32 °C), surface 5 °F above dew point |
| Storage | Original packaging, indoors, out of direct sunlight, 40–100 °F (4–38 °C); keep from freezing |
| Size | 5 Gallon Pail |
| Shipping weight | 52.5 lb (23.8 kg) |
| Availability | In stock |
| Cortec product number | 12400465 |
Solvent Recycling Systems is an authorized Cortec® distributor. See the full Cortec VpCI line, browse the VpCI product selection guide, or contact us for volume pricing and lead times.
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