Everbuild Black Jack(r) 903 Bitumen Trowel Mastic is a black, heavily filled, bituminous compound with added fibres for reinforcement, that is applied by trowel. It is used primarily for patching holes in roofs and bituminous coatings. 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.