BMI 777 Polymer-Modified Base Coat

Polymer Modified Base Coat

BMI 777 is a high-performance, fiber-reinforced, dry-mix, polymer modified, cementitious base coat specifically formulated for use with BMI Acrylic system. 

BMI 777 is used to embed reinforcing mesh as part of the base coat for BMI Acrylic systems. 

Where to use

BMI 777 Polymer-Modified Base Coat is used to embed reinforcing mesh as part of the base coat for BMI Acrylic systems. Appropriate substrates: 

  • Exterior fiber reinforced cement or calcium silicate boards
  • Unglazed brick
  • Cement plaster
  • Concrete or masonry
  • Galvanized expanded metal lath 2.5 or 3.4 lb/yd2


Compliance with the following codes:

  • 2009 International Building Code (IBC)
  • 2009 International Residential Code (IRC) 


BMI 777 one 50 pound bag will produce approximately a 5-gal mixture. Add 5-6 quarts of clean potable water into a clean plastic container. Add BMI 777 slowly while constantly mixing with a twister paddle or equivalent mixing blade, powered by a drive at 500-1200 rpm. NOTE: A minimum 7 amp drill works best for Portland cement based materials. Thoroughly mix until uniformly wetted, adjusting consistency with a small amount of water or BMI 777. Allow the material to set for 3-5 minutes then re-temper, adding a small amount of water if necessary. Material must be free of lumps before using.

If using a mortar mixer add 5-6 quarts of clean potable water for each 50 pound bag of BMI 777. Add the BMI 777 while the mixer is running. Let mix 3-5 minutes, then run mixer for another 2-3 minutes to break the set adding a small amount of water if necessary to adjust workability. The pot life is 1-1.5 hours depending on weather. 

All insulation board irregularities great than 1.6 mm must be sanded flush. Apply BMI 777 to the entire surface of the insulation board. Fully embed the BMI Mesh in the wet base coat troweling from the center to the edge of the reinforcing mesh to avoid wrinkles. The BMI Mesh shall be continuous at all corner and lapped or butted in accordance with BMI's recommendations.

The overall minimum base coat thickness shall be sufficient to fully embed the BMI Mesh. The recommended method is to apply the base coat in two applications. All areas requiring higher impact resistance shall be detailed on the plans and described in the contract documents. The application shall be in accordance with BMI's recommendations.


BMI 777 50 lb. bag covers appx. 120 sq/ft of surface, depending on job conditions, applications techniques, etc. 


Surface Burning Characteristics - ASTM E 84
Water Vapor Transmission - ASTM E 94 Procedure B
Accelerated Weathering - ASTM g 23 (Carbon Arc)
Freeze-Thaw Resistance - ASTM E 2485
Water Resistance - ASTM D 2247
Tensile Bond - ASTM C 297/ E 2134
Water Penetration - ASTM E 331
Ignitability - NFPA 268

Working Time:
After mixing the work time of BMI 77 is appx. 1 to 1.5 hours, depending on ambient weather conditions. 

BMI 777 bags must be protected from moisture and weather. The bags shall be stored off the ground in a cool dry location out of direct sunlight. IF the BMI 777 is warm or hot the pot life of the BMI 777 mixture will be reduced. The shelf life is 1 year from the date of manufacture when properly stored in unopened bags. 

Drying time is dependent on the air temperature and relative humidity. Under average drying conditions (70°F) BMI 777 mixture will dry in 24 hours. Protect work from rain for at least 24 hours. Being a cementitious product, the BMI 777 mixture develops full strength in 28 days.