The AF 721 System is a flakeglass filled vinyl ester resin that is applied to a thickness of approximately 40 mils. Armor Flake 721 bonds to steel, wood, and concrete. Used to line tanks, sumps, trenches, and pump bases that are exposed to strong chemicals, Armor Flake 721 demonstrates very good chemical resistance, toughness and resistance to abrasion. The three coat system is easily applied by spray. The three components of the system are:

  • AF 721-1 Primer – vinyl ester resin
  • AF 721-2 Spray Grade Lining – flakeglass vinyl ester resin
  • AF 721-3 Sealing Coat – vinyl ester with wax added

Chemical Resistance

Armor Flake 721 has exceptional chemical resistance to acids and chlorine. Contact the Wil-Cor, Inc. Technical Department for chemical resistance in specific conditions.


  • High resistance to acids
  • Easy application
  • Bonds to steel, wood or concrete

Physical properties

Color Off White
Service Temperature Limit 220 °F
Flash Point 85 °F
Tensile Strength, (ASTM D-638) @ 77 °F 11-12,000 psi
Tensile Modulus, (ASTM D-638) @ 77 °F 4.9 x 10-6
Flexural Strength, (ASTM D-790) @ 77 °F 16-18,000 psi
Flexural Modulus, (ASTM D-790) @ 77 °F 4.5 x 10-6
Barcol Hardness (ASTM D-2583) 35-40
Elongation % 3 – 5
Heat Distortion Temperature 210 – 220 °F
Adhesive Properties, (ASTM D-1002 Modified)
Carbon Steel 800
304 Stainless Steel 800
2024T3 Aluminum 970
Dielectric Constant, (ASTM D-150) 77 °F and 1KHz 3.38
Dissipation Factor, (ASTM D-150) @ 77 °F and 1KHz 0.003

Installation Recommendation

Wil-Cor, Inc. Recommends supervision by Wil-Cor or that this product be installed by experienced fiberglass installers. Preparation, mixing and application information is provided for installers with adequate installation experience.


All components of the Armor Flake 721 Lining system are catalyzed with Armor Plate 60, methyl ethyl ketone peroxide. The mixing ratio is 1.5 – 2.5 oz. of catalyst for each gallon of AF 721-1, AF 721-2, or AF 721-3. NEVER use more than 2.5 oz. of catalyst per gallon of Armor Flake 721 component.

Catalyzed Armor Flake 721 components have a short pot life. Mix only enough material to use during a short period. Inhibitor may be added to extend pot life if needed; consult with your Wil-Cor representative.

Begin the mixing process with 1 quart of AF 721-1, AF 721-2 or AF 721-3, and the proper proportion of catalyst. Measure the quantities of catalyst and component carefully, because only a small amount of catalyst is necessary for each quart of component.

After the catalyst and component are thoroughly mixed, remove the material from the mixing pot and quickly spray or roll over the surface. Catalyzed material will not set up as quickly if it is not concentrated in the pot. Immediately follow the initial spreading process with a thorough application procedure.

If the applied material does not set up within 3 to 4 hrs, the amount of catalyst in the mixture may be increased. DO NOT add more than 2.5 oz. of catalyst per gallon of component. If using a conventional pot, mix material prior to pouring into the paint pot. DO NOT mix MEKP in the paint pot.

Surface Preparation

For Concrete:

  • 1All surfaces must be clean. Remove all dirt, oil, grease and contamination by sandblasting or acid wash.
  • 2All surfaces must be sound. Remove laitance, powdered concrete, or weak concrete by sandblasting.

For Carbon Steel:

  • 1All surfaces must be clean. Remove any oils, greases, or chemicals and sandblast to white metal.
  • 2Prime the surface immediately with Armor Flake 721-1 Primer to prevent rusting. The primer is not necessary if the Armor Flake 721-2 lining is to be applied within 8 hours of sandblasting.

For Stainless Steel:

  • 1Sandblast surfaces using extra large grit to achieve a deeper anchor pattern for better adhesion.
  • 2Prime the surface with AP 784 prior to application.

For concrete, carbon steel, or wood: The surface to which AF 721 is applied should be smooth, without cracks, pits, or sharp burrs. Rough areas may be smoothed or filled with AP 705, a catalyzed putty material, or may be topped with a laminate consisting of a 1.5 oz. mat or cloth tape saturated with AF 721-1 Primer. All baffles, nozzles and flanges should have a laminate applied before the AF 721-2 Primer is applied.


Armor Flake 721-2 Lining:

  • 1Armor Flake 721-2 is applied by spray.*
  • 2AF 721-2 may be applied after the AF 721-1 Primer and any patched areas are hard to the touch.
  • 3Two (2) 20-mil or four (4) 10-mil applications of Armor Flake 721-2, to give a 40-mil lining thickness of Armor Flake 721-2 should be applied to the tank shell, and a 60-mil lining thickness of AF 721-2 should be applied to the tank bottom.

Armor Flake 721-3 Sealing Coat:

  • 1Armor Flake 721-3 is applied by brush or roller.
  • 2AF 721-3 may be applied after the AF 721-2 Lining is hard to the touch.
  • 3To obtain a non-skid surface, sprinkle clean, sharp sand on the Armor Flake 721-3, coat while it is still soft. Completely cover the surface with the sand, and after the resin has set, sweep off any loose, excess sand.

* Spray Equipment
The following equipment has been found suitable for spray application; however, equivalent equipment may be substituted.
1 each 5-gallon pressure pot (83-5402) with dual regulators
1 each Binks 18 gun with 68 fluid tip, 368 fluid needle and a 68PE or PB air cap
1 each 0.5″ x 25′ material hose
1 each 0.375″ x 25′ air hose
1 each air valve


The Armor Flake 721 Lining system is not recommended as a lining for alkaline service.


Armor Flake 721 components are available in stock sizes of 1 quart, 1 gallon and 5 gallon.

Coverage and Estimating

The theoretical coverage of the Armor Flake 721 components

The theoretical coverage of the Armor Flake 721 components
AF 721-1 Primer 100-150 sq. ft/gal (Depends on surface texture)
AF 721-2 Lining 30-40 sq. ft./gal (Provides 40-50 mil thickness)
AF 721-3 Sealing Coat 100 sq. ft./gal

Shelf Life

Resin Solution, Flammable Liquid

Freight Classification

Armor Flake 721 components have a shelf life of approximately 3 months when stored under dry conditions, around 75 °F.


For Industrial Use Only! – Flammable Liquid

Resin Component

  • Causes eye or skin irritation. Always wear suitable clothing to minimize skin Contact.
  • Vapor caused headache, dizziness, nausea and unconsciousness. Area must be ventilated. If inhaled, remove victim to fresh air. Give artificial respiration if not breathing.
  • For eye Contact, flush with water immediately.
  • For skin Contact, wash with soap and water immediately. Remove contaminated clothing.
  • If swallowed, give large amounts of milk or water to drink and seek immediate medical attention.
  • Flammable. Keep away from all sparks, flames or heat. Extinguish fires with foam, dry chemical, carbon dioxide or water spray.

Hardener – AP 60 (Methyl Ethyl Ketone Peroxide)

  • Store in a cool place away from all sources of heat.
  • NEVER store near cobalt naphthenate or other promotors, accelerators or strong reducing agents.
  • Strong irritant. Ingestion can be fatal. If swallowed, induce vomiting and call physician.
  • For eye Contact, flush with water for 30 minutes and call physician immediately.
  • For skin Contact, wash with soap and water immediately. Remove contaminated clothing.

Before use, review Material Safety Data Sheet for further information. Read and follow the hazard information and first aid directions on each product label before using.