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Black Jack 903 Bitumen Trowel Mastic - 5 Litres


This Black Jack (903) Bitumen Trowel Mastic is a versatile solution for efficient sealing and filling across various surfaces. This trowel-applied product boasts a black, heavily-filled bituminous compound fortified with fibres for added reinforcement. While it forms a durable...Read More

£27.00 Incl. VAT
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This Black Jack (903) Bitumen Trowel Mastic is a versatile solution for efficient sealing and filling across various surfaces. This trowel-applied product boasts a black, heavily-filled bituminous compound fortified with fibres for added reinforcement. While it forms a durable surface skin, the mass beneath retains flexibility, accommodating moderate movements with ease.

With a straightforward application process, this Black Jack Bitumen Mastic is ready to use with no thinning required. From waterproofing and stopping to bedding, bonding and sealing, it is perfect for addressing cracks and holes in mastic asphalt, roofing felt, corrugated iron, metal guttering and downpipes. It also adheres to cast iron, fibre cement, slates, lead, copper, zinc, concrete and timber. With a coverage of 3 litres per square metre at a 2mm wet thickness and a drying time of 24 hours to develop a skin surface, it offers a reliable solution.

Features & Benefits: Black Jack 903 Bitumen Trowel Mastic - 5 Litres

  • Trowel-applied compound with black, heavily-filled bitumen and added reinforcing fibres
  • Forms a surface skin while maintaining a soft mass for moderate movement
  • Ideal for sealing and filling cracks and holes
  • Compatible with mastic asphalt, roofing felt, corrugated iron, metal guttering and downpipes
  • Ready to use without thinning
  • Mainly used for waterproofing, stopping, bedding, bonding and sealing
  • Adheres to/fills holes in various surfaces
  • Coverage of 3 litres per m², giving a 2mm wet thickness
  • 24-hour drying time, develops a surface skin with elastic mass for many months
  • 24-month shelf life from date of manufacture in undamaged containers

Simply apply it with a steel trowel or putty knife for efficient coverage. When dealing with cracks and holes, force the compound into the crevices, finishing with a 25mm band at a 3mm thickness along the length. For larger areas, employ a closely woven glass fibre membrane embedded in the compound and overlap the hole or crack by 50mm, allowing for a seamless, reinforced finish after drying with a second coat.

Surface Preparation

  • Ensure your surfaces are thoroughly sound, stable, clean and dry for optimal adhesion and longevity. Prepare metal surfaces by employing a wire brush to effectively eliminate any rust present. For sustained protection over the long term, initiate the process with a rust-inhibiting product like red lead or zinc phosphate. Rid the surface of any loose or blistered paint to ensure a smooth application. In the case of newly galvanised surfaces, either roughen them up using a wire brush or treat them with a specialised etch primer.
  • If the surface retains dust post-preparation or is coated in weathered bitumen, finish the preparation process by priming with Black Jack bitumen primer. Allow ample time for the primer to dry.


  • For corrugated iron and fibre cement sheeting: Start by securing any loose hook bolts and applying the mastic around with a trowel. Eliminate any wobbly screws, re-bed them with washers in the mastic and tighten. To achieve a flawless finish, seal the top with an additional layer of mastic, trowelling it for a smooth surface. If the sheet displays cracks, initiate a thorough cleaning and priming process using Black Jack bitumen/flashing primer. Apply a bandage strip of glass fibre, fully embedded in the mastic. Once dry, layer it with Black Jack bitumen/flashing primer, followed by a coating of Black Jack bitumen paint. Employ the same method for sealing side and end laps in corrugated sheeting.
  • For tiles: Enhance their integrity by using Black Jack mastic to point up the butt edges of ridge tiles, fillets and slates.
  • For lead and zinc surfaces: Address cracks and pinholes by meticulously trowelling over them. Reinforce as necessary with a woven glass membrane, ensuring full embedding and coverage.
  • For felt: Reattach any loose sections using Black Jack roof felt adhesive. Apply Black Jack bitumen mastic, and for added protection, overcoat with Black Jack all-weather coating. Keep in mind that the felt must be entirely dry before applying the mastic for optimal results.

Please note:

  • Before applying, surfaces should be repaired, dry and clean, as well as free from loose debris, dirt, grease and rust. A stiff-bristled brush should remove algae and fungus growth, then areas can be treated with Everbuild Fungicidal Wash to kill spores and prevent regrowth. Porous surfaces can be primed with a coat of Black Jack Bitumen Primer.
  • After 24 hours, check all bonding for full adhesion. Make sure to check all laps and if in doubt, press home or roll any felt that lacks adhesion.
  • Tools can be cleaned with paraffin or white spirit and spills should be wiped clean before the felt adhesive is set.
  • Do not use in places where subsequent solvent contact is likely. Avoid inhalation of vapours in tight spaces. Nail down the first felt layer on timber roof structures to meet BS 8217-1994.
  • Black Jack Roof Felt Adhesive contains a flammable solvent. Normal fire precautions must be taken during storage and use. Store in the original container in cool dry conditions and keep clear of sources of ignition.
  • If you plan to place a large order of this product, please note that it will be sourced directly from the supplier. As a result, there will be an extended lead time of 10-12 days. If you require more information regarding this, please feel free to contact our friendly sales team who will be more than happy to assist you.


Length 1mm Depth 1mm Width 1mm

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Black Jack 903 Bitumen Trowel Mastic - 5 Litres

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