Intumescent paint coating frequently-asked questions for architects

Only approved top coats can be applied over intumescent coatings.

Contact the coating manufacturer - or visit their website - for a list of approved top coats for the coating in use.

Only intumescent coatings tested and approved for external (exposed to weather) use are suitable.

Water-based intumescent coatings are not suitable for external applications, even if coated with a top seal. They are formulated for use only in fully protected dry, internal locations.

Intumescent coatings are not costed by a square metre rate.

The thickness of the coating relates to the size of the steel members to be fire rated and the designated FRL (fire rating limit). The heavier the steel, the less coating thickness required to achieve the FRL.

If the steel to be fire rated is concealed from view, is located internally and there is no urgency for the construction time then vermiculite will be less expensive in pure application cost than intumescent for a 2 hour FRL.

Intumescent coatings themselves cannot be coloured.

Most intumescent coatings can have an approved decorative/protective paint system applied over them which will provide a choice of colours.

This varies on a product-by-product basis s contact the coating manufacturer for futher details.

Generally, no.

Intumescent coatings are very thick (72% volume solids or higher) and are usually applied using airless spray equipment to achieve an acceptable level of finish.

This also allows for accurate measurement of applied film thicknesses. Small areas that are not required to have an architectural-level finish may be touched up by brush.

Water-based intumescent paint coatings are formulated for application on-site as they are more susceptible to damage from transport/handling.

Also, off-site coating facilities would be tied up for a considerable amount of time as the water-based intumescent coatings, depending on the film thickness required, may need to be sprayed in multiple applications over a number of days. They would need extended drying in good weather conditions to cure correctly.

Most solvent-based intumescent coatings can only be applied off site due to their high VOC levels.

There are some hybrid intumescent coatings formulated for both off-site and on-site application. They offer ‘fast track’ rapid curing, high-build, single-coat application, low VOC, primer-less system.

This will depend to a great degree on what load the steel is supporting and varies case by case and product by product.

You should speak to the manufacturer of the coating to be used for a more definitive answer.

The three numbers represent the FRL for the structural adequacy (load), integrity (flames, gas, smokes) and insulation (temperature).

Generally intumescent paint for structural steel can only achieve the fire protection for the first figure - structural adequacy.

An intumescent-coated structural steel member could not prevent the movement of smoke and heat from one area to another.

Therefore intumescent coatings can only achieve a 120/-/- FRL (or 90/-/- or 60/-/-) for structural steel.