• Should I put the intumescent strip in the door or frame?

    You should follow the door manufacturer’s instructions regarding intumescent seals. It is important to use the type, dimensions and location of seal that is detailed, as a change to any of these could negate the likely fire resistance performance of the doorset.

  • How can you tell if a fire door needs a smoke seal?


    This ‘S’ decal is used in the FD rating; for example, FD 30S means the fire door has a minimum of 30 minutes resistance AND a smoke sealed door. For smoke seals here we are talking about ‘cold smoke seals’ which handle smoke which has moved away from the fire.


  • What is an intumescent product and what is its application?

    Intumescent materials intended for use with the operating gaps in fire doors are usually marketed as strips either manufactured as such or cut from sheets that are fixed with adhesive into grooves in the door leaf edge or in the door frame opposite the door leaf edge. For other purposes in connection with glazing or installation, other forms of intumescent material such as putty, mastic or preformed and malleable components may be more suitable.

    Often the intumescent strip is housed in a pvc casing, which provides protection from moisture and a more pleasing appearance. Plain colours, wood grains and metallic finishes are available. It is usual that pvc casings are self-adhesive protected by peelable tape.

    These seals are commonly available in a thickness range of 3 ~ 4mm and in widths ranging between 10 and 30mm. The thickness of the intumescent content is between 2 and 4mm. Other proprietary brands are supplied in aluminium carriers that are generally thicker and require a deeper groove. Some brands provide combined low-pressure ammonium phosphate with graphite.

  • What do intumescent strips do?

    The word intumescent means to swell or expand, which is exactly what an intumescent strip does: it swells up when hot, filling the void between two surfaces to create a fire seal.

  • What is the difference between the various types of intumescent seals?


  • Why do I need intumescent seals in my fire door?

    With the advent in 1972 of BS 476: Part 8 and the requirement for positive pressure in the furnace, the introduction of the cotton fibre pad to measure integrity made it necessary to employ intumescent materials in virtually all timber fire door designs.

    These expand on heating to close off operating gaps around door leaves through which hot gas and flames could otherwise pass to the unexposed face of fire doors and cause integrity failure early in a fire test.

  • Does the plastic not burn to create a failure?

    The type of PVC used in intumescent strips are not very flammable and will not sustain flame.

  • What is Intumescent?

    The dictionary definition of Intumescent means ‘to swell, or become swollen’.

    As a product any material which expands under the single introduction of heat may be called intumescent however there is a lot more to the technology than just its reaction.

  • Where do I need to protect Ironmongery?



  • Why use intumescent material?


    A second feature shared by proprietary intumescent products is that they will remain inactive and inert at temperatures below those which are characteristic of a fire. As a result they can be built into fire doors without affecting the normal operation of the door and will only be activated in a fire.

  • How much will an intumescent strip normally expand?

    The amount an intumescent strip expands varies depending on the manufacturer.

    It would not be unusual for an intumescent strip to swell up to 20 times its own volume! However, this does not mean it will satisfactorily seal a gap that large.

  • What do I use at the base of a fire door with reference to intumescents?

    Normally, nothing. The heat rises naturally to create a positive pressure at the upper half of the door, developing a balance of negative pressure at the base of the door and pulling ambient air over the face of the door.

    This renders any heat-activated products useless in this area. Intumescents can be used here on doors where specific problems arise with burn-through at the base, but it would be highly uncommon to use intumescents on the base of a door.

  • What is the difference between Palusol and Graphite?

    Palusol is the trade name BASF give to ‘Hydrated Sodium Silicate’ which expands when exposed to high temperatures.

    Palusol is driven by the water boiling, creating course steam blisters as the material expands.

    Graphite has many forms; Pyroplex Graphite is the latest in a line of highly developed intumescents designed to fulfil the requirements of BS476 parts 20: 22. Graphite is driven by chemical reaction, giving a longer and more controllable expansion.

    Graphites in today’s markets are variable in the pressure formulation and can be almost prescribed to suit, a feature Palusol simply cannot match.

  • How should I choose a brand of intumescent seal?

    Multiple manufacturers offer similar intumescent products, but they all provide different levels of fire protection and function differently. Often times, there are a number of intumescents that can satisfy basic fire protection applications.

    The Certifire seal of approval provides a technical schedule to enable the interchangeability of intumescents called TS35 (technical schedule 35).

    On a bespoke basis and for specification purposes, we recommend you stay with the detailed manufacturer to preserve test evidence. If the specification is performance-specified, speak to our technical department with regards to the door size and construction, and they’ll be able to point you in the right direction.

  • What size of cutter should be used for a standard intumescent strip?

    Most of the major manufacturers make just about a perfect sized width with very little tolerance. Therefore, a 10mm x 4mm strip will need a full 10mm cutter set to 4mm depth.

    The products are made to have a friction fit as well as the self-adhesive tape applied.

    The strips have a tolerance of as little as ± 0.2mm which ensures the strip will fit! Best practice for these strips is a tight fit.

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