Application Guide

The following specification is a typical cold roof application, it can however, be adapted to most warm roof type applications by incorporating the vapour barrier and insulation.

Note – Polyester Underlay to be nailed or fixed using suitable adhesive on combustible type roof decks. Please refer to the ‘Safe 2 Torch’ latest guidelines when using gas torches. Visit

1. Preparing the deck

  1. Make good the deck surface and repair all required areas.
  2. Fit angle fillets along the base of all upstand and parapet walls.
  3. Cut out flashing channel along all upstand and parapet walls.
  4. When deck is clean and dry apply the fast dry primer following the manufacturers instructions.

2. Locating the Venting Layer

  1. Before each run of Underlay is applied, roll out the required amount completely and cut.
  2. Align the felt with a 3″ (75mm) side lap.
  3. Re roll from both ends to the centre. The underlay will then follow the desired path, when applied as described in (4.1 and 4.2).

3. Applying The Underlay

  1. Working from the centre, apply the underlay by directing the torch at the roll slightly above the point at which it contacts the under surface. Move the torch from side to side making sure the bitumen is sufficiently heated to fully bond the underlay.
  2. Care needs to be made not to over torch the underlay. However, a bleed of bitumen needs to be just visible at both edges as the membrane is rolled out.

4. Underlay Detailing

  1. Cut out the upstand detailing and apply where required. A smaller detailing torch may make this application easier. Make sure a good bond is established.
  2. The overlaps for the detailing are the same as the flat runs, leaving a 3″ (75mm) side lap and 6″ (150mm) end lap.
  3. Go over all laps within the underlay and check a correct seal has taken place. Re seal where required using a torch and a trowel or scraper.

5. Locating The Cap Sheet

  1. Locate the cap sheet with the underlay overlap in the centre of the width of the cap sheet roll.
  2. Re roll into the centre as with the underlay (3.3).
  3. On mineral finishes protect the mineral closest to the selvage edge with paste. Normal household wallpaper paste can be used for this.

6. Applying The Cap Sheet

  1. Apply the cap sheet in the same manner as the underlay (4.1).
  2. Make sure a slight bleed of bitumen is visible at both edges.
  3. Care needs to be taken not to mark the mineral finish while the membrane is warm

7. Creating An End Lap

1. When more than one roll is required in the same run, allow 6″ (150mm) end lap.
2. Protect the mineral on the inside of the end lap area with paste.
3. Heat the mineral just enough to scrape the finish off with a trowel.
4. Apply end lap making sure the bitumen is heated enough to create a good bond.

8. Finishing

  1. Cut all cap sheet detailing (see detailing section) and apply using a detailing torch.
  2. Finish all upstands with the required flashing and repoint.
  3. Where mineral finishes have been protected with paste, allow the paste to dry and then carefully trim the bitumen bleed with a handy knife. The paste will now lift like tape leaving a tidy overlap – fully sealed without unsightly bitumen bleeds.

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