Elastomeric Roofing - TOPCOAT MP-300 Rust Inhibiting Primer

TOPCOAT® MP-300 Rust-Inhibiting Primer


TOPCOAT® MP-300 rust-inhibiting primer is a light blue, acrylic water-based, industrial primer/rust inhibitor that must be applied to any areas of rust before TOPCOAT® Flashing Brush Grade or TOPCOAT® Membrane can be applied. Heavy, flaking rust and scale must be removed by scraping, wire brushing, or grit blasting, followed by power washing with water. TOPCOAT® MP-300 primer can be used to brush-treat small scattered areas of rust, or it can be sprayed over areas of widespread rust. It is non-flammable, VOC compliant, and cleans up with water.


TOPCOAT® MP-300 Primer is designed for use on metal and should be applied over any areas of rust that remain on the substrate after pressure washing. All rust areas must be treated with TOPCOAT® MP-300 Primer to prevent further deterioration of the metal roof panels. For use with water-based sealants and coatings only. Do not apply at temperatures below 42°F. Substrate temperatures must be below 120°F when applying product.

  • Used to inhibit further rust and provide added protection

  • Light blue in color to ensure proper application

  • Ideal for use in preventing rust from bleeding through TOPCOAT® Elastomeric Roofing Membrane

  • Non-flammable, VOC compliant, and easy to clean up

  • Limited material warranty available for up to 10 years*

  • Guarantees available for up to 20 years*

  • Available in 5-gallon pails, 55-gallon containers, and bulk totes

For application questions, please contact GAFMC Contractor Services at

Applicable Standards

ASTM B-117, ASTM C-794, ASTM D-21-96, ASTM D-1475, ASTM E-1644

Note: Repair leaks promptly to avoid adverse effects, including mold growth

*See warranties and guarantees for complete coverage and restrictions
** When used as a part of a multi-ply system

TOPCOAT® MP-300 Technical Data
Application Rate: 1 gallon/100 sq. ft.
Application Method: Brush or airless sprayer
Application Temp (air, surface): 42°F – 120°F
Drying Time (75°F, 50% RH): Approximately 2 hours
Wet Mil Thickness: (1.0 Gallon/100SF) – 16 wet mils
Dry Mil Thickness: (1.0 Gallon/100SF) – 6 dry mils
Total Solids (by weight): 50% ± 1%
Total Solids (by volume): 40% ± 2%
Specific Gravity: 1.19 ± 0.1
Weight per Gallon: 9.9 ± 0.5 lbs
Viscosity (75°F): 5,000 ± 1,000 cps
Storage: Store in well-ventilated area at 50°F to 80°F; protect from freezing
Shelf Life: 1 Year
Clean-up: Water before curing


All documents are U.S. English unless otherwise noted

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