Intumescent Paint and Coatings Guide

We provide a full specification service and certification for building control please call for technical advice and product costings on 01935 414012 or email us

All our intumescent paint products have been tested to relevant European or British Standards.

The products have been designed for ease of application and are water borne for environmental and handling considerations.

Fire resistant or intumescent paints and varnishes will create a barrier against fire by forming a foaming char layer above substrates such as timber, steel or plaster. Chemicals within the coating react to heat by creating bubbles of inert gas which are strengthened by both the paint’s own polymer and additives. This non-combustible meringue type layer insulates the substrate and increases the time it takes for the fire to penetrate through. In the case of steelwork, this insulation keeps the metal cool for longer, extending the time it takes to collapse. Intumescent paints are usually rated by time (i.e. 30, 60 or 90-minutes resistance). Customers often think these coatings protect the substrate for the specified time, but this is not the case. The time given is the time it takes for the paint and substrate to fail (i.e. for fire to go through a treated door). Generally intumescent paints will need to comply with EN1364, EN1634 or BS476 Parts 20-23.

Not all substrates can be protected to 30 or more minutes. The level of protection which can be achieved is very much dependent on either the thickness or composition of the substrate. It should be possible to upgrade elements such as structural steel beams and columns or large timber joists. However, it is unlikely thin steel sheet or matchboard and some thin walled hollow section would achieve the minimum of 30-minutes as they have no inherent fire resistance


Fire retardant paints and varnishes will, when applied to combustible surfaces, such as timber, make them much more difficult to ignite to the point where some small fires can self-extinguish. Once a surface has caught fire, the rate of flame spread is much slower. This also reduces the phenomenon of flash-over in confined spaces. Generally these coatings need to comply with either BS476 Parts 6&7 or EN13501-1. Both are accepted under Part B of the Building Regulations. Occasionally these are referred to as intumescent paints, but not all fire retardants are intumescent


In the UK only EU and BS standards are recognized. US standards such as UL and ASTM as well as some DIN and others may not satisfy the requirements of UK building standards.


Intumescent and fire retardant coatings should not be confused with heat resistant paints, which perform a different function. Prospective users should also check that the fire retardant varnish or paint will impart the protection to the surface on which it’s applied. In some cases, although the paint itself is fire retardant, it isn’t a fire retardant treatment for the substrate.


When intumescent paints are used to protect structural elements, such as beams and columns, the test should take into account not just the insulation and integrity criteria, but also the load-bearing capability. This is especially the case with paints used to treat structural steel.


All fire retardant paints, coatings and varnishes have to be independently tested by accredited laboratories with no commercial connection to the producer. All of the coatings and fire retardant liquids supplied by ACS have been independently tested.


ACS can supply a range of coatings for many different substrates

Wood and wood related substrates

S92/FR/P is a waterborne two-pack system, available in both clear and white for interior use only. This fire retardant is designed for application to both bare and painted timber and wood related products, such as plywood, MDF and particleboard. When correctly applied S92/FR/P will give protection to Class B (EN13501-1) or Class 0&1 (BS476 Parts 6&7)

S92/FR is a single-pack fire retardant paint or varnish, which, when used with the correct protective lacquer can protect both interior and exterior timber, such as cladding. S92/FR can also be used with proprietary topcoats such as pre and acid cat lacquers, so is useful for high quality panel finishing.

FC0 is a clear waterborne impregnating fire retardant treatment for bare timber. Unlike some other treatments, FC0 can be used on softwood, hardwood and modified timber such as Accoya and Thermowood. Once dry, FC0 doesn’t require a protective topcoat although it can be used in conjunction with the ACS Woodbead to give added protection and resistance to water and dirt pick-up.

S42/01/E and S42/02/E are white (01) and clear (02) intumescent paints suitable for use as both fire retardant and fire protection coatings. Providing certain criteria are met, both systems are capable of providing not just Class B (Class 0&1), but 60-minutes protection to exterior timber cladding and 30-minutes insulation, integrity and load-bearing capacity to timber beams and floors.


Intumescent paints for plasterboard and lath and plaster

S105/SPC is a microporous water-based paint, used to increase the fire resistance of skimmed or skimmed and painted plasterboard. Two coats applied to 12.0mm ceiling board or 9.0mm wall board will give 60-minutes fire resistance. The product can be used with a number of different topcoats to give a fully decorative finish. This system has also been independently tested on lath and lime plaster to give 74-minutes insulation and integrity.


Intumescent paint for steelwork

S83/ISC is a relatively thin-film, smooth intumescent coating system for application to new, primed and previously painted steelwork. It offers protection for up to 90-minutes depending on the size and orientation of the steel and is suitable for both on and off-site application. There are a range of protective topcoats available, which allows both interior and exterior application. S83/ISC can be used to protect a wide range of structural steelwork, including RSJ, UB, UC, PFC and hollow steels.


ACS provides a full specification service and we recommend you contact us to ensure you have the correct product for the job. On completion, we can, if required, issue a Certificate of Supply for Building Control. Contact us at or call 01935-414012 (outside the UK +44 1935-414012)



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