50 lbs. bag

BMI 777 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.



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.


Do not over water BMI 777. It shall not be used to adhere EPS directly to wood-based substrates. Mixing paddles and pails must be clean. Contamination from previous mixing will lead to a short pot life.

Substrate and air temperatures must be 40*F or higher and rising at time of application. Wear protective eyewear and clothing since the product contains cement, which can cause irritation. Avoid working in direct sunlight and keep mixed BMI 777 in the shade.

Surface Preperation:

Surfaces must be clean and free of bond-inhibiting materials such as dirt, dust, rust, grease, oil, efflorescence, mildew, fungus, form-release agents, or any other contaminants. Remove or repair any loose paint, mortar, stucco, concrete or masonry by water-blasting, sand-blasting, scraping or using a wire brush. Substrate should be securely fastened. Repair all cracks with appropriate patching compound. Mask off area accordingly. Prime all surfaces with BMI Primer 100 before applying BMI Acrylic 200.

Acceptable 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 lbs/sq. yd.


All insulation board irregularities greater 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 so as to avoid wrinkles. The BMI Mesh shall be continuous at all corners 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, application 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 777 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.