Everbuild Black Jack 903 Bitumen Trowel Mastic Bitumen Trowel Mastic is a trowel applied black heavily filled bituminous compound with added fibres for reinforcement. The product forms a surface skin, but the mass below remains soft to allow for moderate movement. Suitable for sealing and filling holes in mastic asphalt, roofing felt, corrugated iron, metal guttering and downpipes. Suitable for waterproofing, stopping, bedding, bonding and sealing. Adheres to/fills holes in mastic asphalt, roofing felt, corrugated iron, cast iron, fibre cement, slates, lead, copper, zinc, concrete and timber.