Intumescent Coatings

Explore the most frequently asked questions on intumescent coatings here...

What environments can Nullifire intumescent be applied in?

Nullifire coatings may be used internally and externally and have been tested in accordance with ISO 12944 up to a C5 environment. Refer to Nullifire Specification Control Guidance Note for further information.

What is the difference between water based and solvent based intumescent coatings and where can they be used?

Water based intumescent are designed for use up to C3 environments whereas solvent based intumescent may be used up to C4. Solvent coatings can be more durable to external weather elements when combined with a suitable topseal. Refer to Nullifire Specification Control Guidance Note for further information.

Can I fit attachments to steelwork coated with Nullifire intumescent?

Yes, guidance from the ASFP state attachments should be considered as part of the beam and duly protected against fire. Refer to NTN002 for further information.

Do connection bolts require protecting?

Yes, the ASFP advise bolt heads should have the same fire resistance as the primary steel section to provide structural integrity. Refer to NTN018 for further information.

There is an unknown coating on the steelwork. Can Nullifire Intumescent be applied above?

With unknown coatings, there is a possibility that under fire conditions they may fail and delaminate from the steel, removing any additional coatings applied above. We would recommend all unknown coatings to be removed with the surface being prepared to SA2.5 standard to then allow a new tested and documented system to be applied.

The steelwork has timber applied to the structural steel coated with Nullifire intumescent. Would this pose an issue?

Timber will prevent the intumescent from expanding under fire conditions. Where timer directly covers the coating, the coating will not provide the required protection. We would recommend an independent structural fire engineer be contacted to discuss the fire design and the suitability of using an intumescent coating. Refer to NTN024 for further information.

The client wishes to install a board around Nullifire intumescent coated steelwork for decorative purposes. Would this pose an issue?

Thin film intumescent are reactive coatings, swelling under fire conditions to provide a protective char. Guidance from the ASFP state that an expansion zone a minimum of 50 x Dry Film Thickness should be allowed for. Refer to NTN036 for further information.

Can a standard decorative paint be applied on to Nullifire intumescent?

It is possible to overcoat Nullifire Intumescent coatings with a standard paint however, this may reduce the expected lifetime of the system. Contact Nullifire Technical Service for more information.

Can Nullifire intumescent be used in conjunction with other fire rated systems such as other spray systems or boarding on a single structural steel element?

The ASFP have provided Technical Guidance Document 8 Code of practice for junctions between different fire protection systems when applied to load bearing structural steel elements. TGD8 states it is best practice to use the same product or system on whole structural steel sections. TGD8 may be downloaded from the ASFP’s website (

Do Nullifire intumescent coatings provide insulation values?

Thin film intumescent coatings are tested to provide structural integrity under fire conditions. Where an insulation value is also required, an alternative system such as encasement should be considered.

Can Nullifire intumescent be used on cold rolled steelwork?

Cold formed steelwork are generally formed from thin gauge steel. This loses strength in fire quicker than hot rolled steel. In general, the critical failure temperature of cold rolled will be significantly less than hot rolled section. This combined with higher section factors due to the profile thickness can make protecting with thin film intumescent problematic. We would recommend an independent structural fire engineer be contacted first to determine the limiting temperate then refer to the relevant loading tables.

Why is Fire Resistance expressed differently for Nullifire intumescent products?

It is simply down to the testing that is needed to generate the approvals used to market the products. Some tests are absolute i.e., the test or approval criteria are black and white where a test sample has to achieve the set criteria. Other tests are not absolute and the approval depends on a series tests results to be analysed together to produce an assessment. An example is intumescents for structural steel. Because of the multitude of steel sizes and geometries that exist, performance needs to be determined over a range that the product intends to be marketed for.