Protal ST Epoxy Mastic by Denso

Surface Tolerant Liquid Epoxy. Resists long-term exposure to water.

Available in:

1/2 Gallon kit
1 Quart Kit 


Denso Protal ST Epoxy Mastic is a two-pack, high-solids, fast-drying epoxy coating for application directly onto wire brushed rusty steel substrates to SSPC-SP2/3. Its good penetration and adhesive properties ensure excellent protection in long-term exterior exposure.


Denso Protal ST Epoxy Mastic is used wherever steel grit blasting is not possible. Protal ST Epoxy Mastic can be used alone or in combination with other topcoats for long term exposure to water in applications such as: structural steel, pipe externals, pipe racks, tanks, offshore platforms, locks, gates, and bridges.


  • Minimal surface preparation (SSPC-SP2/3)
  • Long-term exterior protection
  • Excellent water/sea water resistance
  • Good resistance to acids and alkalis
  • Good flexibility, hardness and adhesion
  • Good impact resistance
  • Low VOC’s


Prepare surfaces by removing all loose scale, rust or other foreign matter in accordance to SSPC-SP2 “Hand Tool Cleaning” or SP3 “Power Tool Cleaning”. High pressure water wash of 3,000 - 7,000 psi is also suitable. This can be achieved using power brushing or machine grinding. If the surface is severely corroded, chipping hammers and needle guns will be required. The surface should finally be cleaned with a vacuum cleaner, clean dry with compressed air or a clean brush. The steel should then have a faint metallic sheen. Use as supplied in pre-weighed packs Part A (base component) with Part B (hardener). Pour all of Part B into Part A and thoroughly mix with a power whip for at least 2 minutes.

The substrate temperature must be a minimum of 5°F (3°C) above the dew point temperature before proceeding with the coating operation. The first coat can then be applied by brush or spray to a wet film thickness of 10 mils (8 mils DFT). Check the film thickness of the coating regularly with a wet film gauge during application. Minimum wait time for overcoating is 4 hours at 77°F (25°C).

Spraying is carried out using a 45:1 airless spray pump and a 21 to 31 thousands of an inch tip. Below 59°F (15°C), add 5% Denso Protal Thinner No. 55. Apply the second coat at 10 mils wet film thickness in the same manner as the first. When dry, a final weather resistant top coat such as a water based acrylic or polyurethane can be applied by brush or spray.

Technical Data


Pot Life @ 77°F (25°C) (ASTM 2196)

1 hour

Touch Dry @ 77°F (25°C) (ASTM D1640)

3 hours

Theoretical Wet Film Thickness (typical)

10 mils per coat

Theoretical Coverage

163 ft2/gallon @ 10 mils
4 m2/liter @ 10 mils

Solids by Volume


Mixing Ratio by Volume

2 Parts Base:1 Part Hardener

Application Temperature

-20°F to 125°F (-29°C to 52°C)
Note: If temperature falls below 50°F (10°C), surface must be preheated.

Theoretical Coverage

14 ft2 (1.3 m2) / 30 mils / liter

Recommended Paint System
     First coat Denso Protal ST 8 mils (DFT)
     Second coat Denso Protal ST 8 mils (DFT)
     Final coat acrylic, enamel or polyurethane

8 mils (DFT)
8 mils (DFT)
2 mils (DFT)

Overcoating Time (min.) (ASTM D3359B)
     50°F (10°C)
     60°F (16°C)
     77°F (25°C)
     95°F (35°C)

12 hours
8 hours
4 hours
2 hours

Shore D Hardness @ 77°F (25°C)


Adhesion to Steel (ST2) (Elcometer pull-off)

1,800 psi

Hot Salt Fog @ 95°F (35°C) (ASTM B117)

1500 hours

Humidity Test @ 104°F (40°C) w/100%

1500 hours


Light gray

Handling & Storage



Store the containers in a dry, well ventilated area. The containers should be kept tightly sealed. Shelf life: 2 years.


1 quart, 0.5 gallon kits and 1.0 gallon kits (1.9 liter kit or 3.8 liter kit).
Special kit sizes available.

Health & Safety

Spray or brush under well-ventilated conditions. Wear suitable protective clothing and glasses. See material safety data sheet..