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Bostik Bituminous Mastic for Waterproofing Roofs - 2.5L

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Bostik Bituminous Mastic for Waterproofing Roofs - 2.5L

  • Bostik Bituminous Mastic For Roofs is a multi-purpose trowel grade bituminous material for waterproofing, stopping, bedding, pointing and sealing.
  • It can be applied to mastic asphalt, roofing felt, currugated iron, cast iron, fibre cement, slates, lead, copper, zinc, concrete and timber.
  • It dries to a flexible black material which remains soft and pliable for a long time after application.
  • Size: 2.5L   (Available in sizes 1.2L and 2.5L)


  • Bostik Bituminous Mastic For Roofs must only be applied to surfaces that are completely dry.
  • Ensure that when applied to bitumen felt no moisture is contained within the felt.
  • Ensure the roof surface is structurally sound, clean, dry and free from surface contaminents such as grease, oil, dirt and loose materials.
  • Remove any organic growth i.e. moss or lichen with Fungicidal Wash.
  • If the surface is either dusty after cleaning, or covered with weathered bitumen, prime with Bostik Penetration Primer for Roofs and allow to dry.
  • To assist application in cold weather , store the amterial in a warm room overnight prior to use.


Apply with a steel trowel or putty knife.

Crack / holes:

  • Force Bostik Bituminous Mastic into the cracks, covering over the area to be treated by 25mm either side, at a thickness of 3mm.
  • For large cracks and holes apply over areas to be treated and embed a closely woven glass fibre membrane into the compound to overlap the crack or hole by approx 50mm.
  • Allow to dry and then apply a second coat, fully covering the reinforcing membrane.

Corrugated iron / fibre cement sheeting:

  • Tighten loose hook bolts and trowel around with Bostik Bituminous Mastic.
  • Remove loose screws then rebed screws and washers in Bostik Bituminous Mastic and tighten; top seal and trowel to a smooth finish.
  • If a sheet is cracked: clean, prime and apply a bandage with a strip of woven glass membrane embedded in Bostik Bituminous Mastic.
  • Allow to dry, then overcoat.
  • Where it is required to seal side and end laps in corrugated sheeting use the same technique.


  • Point up butt ends of ridge tiles, fillets and slates with Bostik Bituminous Mastic.

Lead and Zinc:

  • Trowel over cracks and pinholes, where necessary reinforcing with a fully embedded and covered woven glass membrane.


  • Re-adhere loose felt especially flashings and details, then seal joints with Bostik Bituminous Mastic.
More Information
General Colours Black
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