Intumescent Paint for Structural Steel and Cast Iron (WI & WO)

  • Water based Intumescent for structural steel.

  • For 30 mins protection: 1 thick coat – 2.5kg 4 linear m, 5kg 8 linear m, 20kg 32 linear m – if in any doubt please contact us.

  • For 60 or 90 minutes protection: contact us for further advice specific to your project.



ISS-WI & WO intumescent Steel Coating


How it works

The heat of a fire triggers a catalytic reaction, causing the expansion of an insulating char layer up to 50 times the paint thickness. This layer keeps the steel below its critical temperature, thus maintaining the structural integrity of the building.


Fire testing

Product performance assessment is based upon UKAS/EGOLF Fire Test Laboratory Certification to BS 476 Part 21 - Fire Resistance to load bearing elements of structures. For certification and compliance with regulations the manufacturer will supply a Certificate of Supply on request.


Preparation and Pretreatment

Steel and cast iron should be free from rust and millscale and primed with HBP Primer to 75 microns DFT ( or alternative good quality anti-corrosive primer compatible with intumescent paints) in accordance with manufacturers instructions. Treat galvanised surfaces with “T” wash/Mordant solution & prime with zinc phosphate or other primer for steel. HBP Primer may be left without further overcoating or decorated with appropriate conventional paint where no fire resistance is required.


To Specify

  • Dry Internal: Apply ISS-WI & WO in accordance with intumescent-paints film thickness schedule to acheive 30, 60, 90, 120 min.
  • Visible or occasional modest damp internal areas: Also apply 1 good coat FR Paint
  • Wet or External Under Cover: Apply 2nd coat Flame Retardant paint
  • Full External Exposure - Contact Technical Dept.

We are happy to provided specifications and quotations - please use our structural steel specification form to ensure we cover all aspects of your fire protection and decorative requirements in our quote. We accept any order size.


Prior to application the contractor should contact the Technical Department (see below) to obtain a basecoat application schedule.


For help please speak to the technical team on: Tel: 01329 841 416 or Email:



  • ISS-WI & WO may be applied by brush, roller or airless spray. To achieve the best finish in the shortest time, spray application is recommended. Prior to application the contractor should contact the Technical Department and obtain a basecoat application schedule. To assist correct application in accordance with this schedule, a wet film gauge will be supplied with the order. Further wet film gauges will be provided on request.
  • Maximum wet film thickness per brush coat – 800 microns
  • Maximum wet film thickness per spray coat – 1400 microns



Brush/roller application

  • Surface touch dry: minimum 2 hours, handle min 24hrs
  • Recoat: minimum 6 hours
  • Overcoating with Flame Retardant finish: minimum 24 hours


Spray application

  • Surface Dry: minimum 4 hours
  • Recoat: minimum 10 hours
  • Overcoating with Flame Retardant finish: minimum 48 hours


Spray Equipment

Airless Spray Pump


Use equipment recommended by manufacturer for the application of high viscosity intumescent paints.

  • Filter size 30 mesh. 10mm hose 3/8” diameter with no whip end

Tip Size

  • Tip Size 319, 321, 419, 421

Care should be taken to clean filters regularly. Cleaning should be undertaken with water.


Colours, Finishes & Sizes

  • ISS-WI & WO - 20 kg, 5 kg, 2.5 kg
  • Flame Retardant gloss, eggshell, WB satin, WB matt
  •  BS4800, RAL, 2.5 lt + 5 lt cans


Intumescent compounds and resin binders, with high opacity pigments.



The EU VoC limit for structural steel intumescent paints is 500 gm / litre. This product contains 398 gm / litre.


Technical Advisory And Estimating Service

Our in-house estimators provide realistic, confidential guidance on project costings to contractors and quantity surveyors. They also provided expert advice and assistance with all aspects of specification and application.


Application Conditions

  • Maximum Relative Humidity 80%
  • Minimum ambient temperature 4°C
  • Minimum Steel Temperature 3°C above Dew Point



We have technical representatives who provide assistance in the selection and specification of the products on this site and should be consulted for exact installation and product suitability. Ensure an early engagement with ourselves, designers, main contractor and specialist installers before any installation. Other trades and/or manufacturers may need to be consulted. For in-depth information, specification and technical advice please call our Head Office on Tel: 01329 841 416 or Email:



All interested parties, designer, specifier, main contractor and specialist installers should provide access to allow the fire stopping seals to be regularly inspected and maintained, as well as records kept of such maintenance at minimum periods of 12 months, as required by the Regulatory Reform Order, and repaired if necessary. Reference should be made to ASFP TGD 17 – Code of Practice for the Installation and Inspection of Fire Stopping.



It is vital that those entrusted to design or install a fire stopping product have the necessary levels of competence to undertake the task professionally and thoroughly. The level of competency required will be commensurate with the expected complexity of the building. All designers must eliminate, reduce or control foreseeable risks that may arise during installation, construction or maintenance when preparing or modifying designs. Clients should ensure that the principal designer and principal contractor carry out their duties under CDM regulations. The ASFP foundation course in passive fire protection provides essential knowledge as part of demonstrating competency and understanding in this key fire protection specialism.


Additional Notes

This product can only be supplied once the Steel Paint enquiry form has been completed and approved by the manufacturer: Click the following link to go to the Steel Paint Form: Steel & Cast Iron Order Form.


Health and Safety

ISS-WI & WO Paint is a low-odour, water-based coating, making it user and environmentally friendly. The range of topcoats are either water-based or 2010 compliant and safe to use in accordance with manufacturer’s instructions.


The product does not present any known health hazards during or after installation. Normal good industrial and personal hygiene practices should be observed. For further information on health and safety please see the Safety Data Sheets (SDS) or please contact the technical team on Tel: 01329 841 416 or Email:


More information / Data sheet

For more information please click the button below to download a printable PDF file for ISS-WI & WO intumescent Steel Coating.

The above information to the best of our knowledge is true and accurate and based upon current test data and is supplied for your guidance only. Customers should satisfy themselves to the suitability of the product in its intended use and no guarantee is given or implied since the conditions of actual use are beyond our control. We disclaim any liability for loss, damage or other expense arising from the use of information, data or products mentioned or referred to and reserve the right to change any details or specifications without notice.

Web Page


Copyright © intumescent-Paint 2022. Unit 9, The I.O Centre, Stephensons Road, Segensworth, Fareham, PO15 5RU

tel: 01329 841 416 | email: