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Intumescent Letterbox Liner - Installation Guide

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NHBC and LANTAC Approval


The purpose of this document is to give guidance to approved contractors and suppliers who are engaged in the fire stopping of service penetrations in walls and doors using the Astro Liner

All service holes through floors and compartment walls must be fire stopped to prevent the passage of fire, smoke and hot gases. The key points for intumescent passive fire protection products are :-

  • Prevent the spread of fire, smoke and hot gases through a building by containing it in the compartment of origin.

  • Maintain the integrity of escape routes from a building.

  • Reduce loss or damage to property from the effect of fire and smoke.

  • Maintain pressure differential between compartments and ventilation channels.

Astroflame Letterbox Liners

The Letterbox Liner / LB System consists of a high performance, self adhesive backed, PVC laminated intumescent material which has been designed to line the aperture of letterboxes in fire resistant doors

On exposure to a fire the liner will rapidly expand (intumesce) to seal the aperture and stop the spread of fire, smoke and hot gases through the door.

The liner has been independently tested to BS476: Part 22: 1987 and can provide in excess of 1 hour fire resistance.

Warrington Fire Research Assessment - 30 minute 44mm liner : 60 minute 50mm liner


Intumescent Liner available in Brown or Red pvc finish.

Letter plates in satin aluminium or brass effect, both aluminium construction.

Supplied in packs containing sufficient material to suit any size aperture up to 270mm x 69mm and can be used in both 1/2 and 1 hour fire door assemblies.

Larger sizes available on request.


The liner can be used in either existing or new letter boxes

To install into existing letterbox, remove the existing front and back plates, enlarge the aperture to suit the addition of the intumescent liner. Ensure that the aperture is clean and free from dust or grease, to ensure a good adhesive bond we recommend that the timber be sealed with either a primer or wood sealer.

Cut the liner to size, remove the release paper from the self adhesive backing, fit top and bottom liners first, pressing firmly into position, then fit side liners in the same manner.

Ensure leading edges of the liners are fitted flush with exterior face of door and that the top and bottom liner are not going to interfere with the operation of the letter box.

Ensure all liners are well bonded into position, trim to width if necessary (minimum 40mm for 60min rating.

Refit existing letterplates, external plate must be sprung, internal must be gravity type and both must be of aluminium construction.

To install into new work simply cut the aperture to the appropriate size then fit as detailed above, finally fit new Astro Letter Plates as detailed in this installation sheet.


Astro liners are manufactured in the EU, meeting the highest quality standard in compliance with ISO EN 9001:2000 . For fire test certification contact Astroflame Fireseals technical department.

Fire Test or Assessment Reports

BS 476 part 22 for in excess of 60mins - Test report : C 100767
BS part 22 - Test report RF 95041

Storage and disposal

Astro liner should be stored indoors. No shelf life is given as this product will not deteriorate in storage.

For additional testing, certification or technical information please contact ASTROFLAME FIRESEALS LTD.

Issue 01/03



Astroflame (Fire Seals) Ltd. Intumescent House
Unit 8, The IO Centre, Stephenson Road, Segensworth
tel 0800 023 2482
(01329 844500)
fax 0800 023 2483
(01329 844600)
tel +44 1329 844500
fax +44 1329 844600




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