Most ventilation air that enters a typical coal mine never reaches the mine working sections. Because of poor stopping construction, the air short circuits to the returns instead. With power costs at the present level and expected to rise, mines are becoming aware that ventilation air is a significant cost of operation. The Bureau of Mines concentrated on practical, low-cost improvements in building concrete block stoppings that would be available to any mine operator. It was found that a strong and airtight block stopping could be built by brushing instead of trowelling on mortars. Using a brush, rather than a trowel, has several benefits. The average mine laborer is more proficient with a brush. The final sealant finish is smooth, and any unsealed holes are apparent. Airtightness is improved at the block joints and around the periphery of the stoppings, where leakage is most prevalent. Finally, in the hands of the mine laborer, this method offers a faster application with less waste.