Intumescent fire protection paints for steel: water-based and solvent-based

What is a thin-film intumescent paint?

An intumescent (reactive) fire protection paint is a coating ranging from a fraction of a millimetre to several millimetres thick which, under normal conditions, looks like an ordinary dense paint film. When heated, it swells into a light, porous “blanket” of char many times thicker than the original film. This layer is a poor conductor of heat and slows the heating of the steel to the temperature at which it loses its load-bearing capacity.

The main application is the steel frames of residential, public, warehouse and industrial buildings designed for a standard (cellulosic) fire. For facilities where petroleum products may burn, there is a separate class of materials — epoxy intumescent coatings, which are covered on the “Hydrocarbon fire” page.

How intumescence works

The paint contains several functional components. At a couple of hundred degrees, the binder softens, the acid source triggers charring of the carbon source, and the blowing agent foams up the mass. The result is a cellular char layer on the steel surface. As long as this layer stays intact and remains attached to the steel, the protection works.

Two practical conclusions follow. First, the paint must bond reliably to the primer, otherwise the expanded char will fall away. Second, the topcoat must not inhibit intumescence — which is why topcoats are selected only from the list tested by the fire protection manufacturer.

Water-based and solvent-based paints: the differences

Parameter Water-based (waterborne) Solvent-based
Odour and fire hazard during application Virtually odourless; no explosion-proof equipment required Contain solvent: ventilation and fire safety measures needed in the work area
Application conditions Sensitive to low temperature and high humidity; dry more slowly in the cold Wider weather “window”; develop their resistance more quickly
Service conditions Mainly dry, heated interiors; in damp conditions only with a protective topcoat Heated and unheated interiors, under canopies; for external use, as directed by the manufacturer
Best place to apply On site, including in occupied buildings On site and in the fabrication shop

There are also intermediate options: high-build single-coat systems and fast-curing three-component coatings applied at the steel fabrication shop so that members can be handled after only a few hours. Whether such a material is water- or solvent-based is always stated in the technical data sheet — that is where to look, not at the name of the product range.

How to choose a paint

Required fire resistance rating

Thin-film paints are most commonly used for ratings of R 15 – R 90; a number of products have approved solutions for R 120. The higher the rating, the thicker the coating and the more closely the cost of the system needs to be examined: at high ratings, non-reactive fire protection often proves more cost-effective.

Reduced metal thickness and section type

The coating thickness is determined from the manufacturer’s tables or calculation software for the specific section: I-section, channel, angle, tube or box section. For the same rating, a heavy column may need only a thin coat, while a light truss made of angles may need several times as much. International tables use the section factor Hp/A (the ratio of heated perimeter to cross-sectional area) instead of reduced thickness — it is the same characteristic viewed “from the other side”.

Critical temperature

Test methods common in CIS countries assess fire protection efficiency up to a nominal critical steel temperature. In European practice, the critical temperature is calculated for the specific member and load level. If the design follows one system of codes and the material has been tested to another, the conversion must be done by a specialist, not a buyer.

Service environment

Compare the site conditions with the limitations in the technical data sheet: exposure category, humidity, temperature swings, likelihood of condensation. In unheated warehouses and under canopies, a water-based paint without a topcoat is a frequent cause of complaints.

Compatibility with the corrosion protection system

The primer is selected from the fire protection manufacturer’s list. If the steelwork arrives already primed by the fabricator, check the primer product and its thickness in advance — this determines whether the paint can be applied directly over it or an additional coat will be needed.

Common mistakes

  • Buying paint “by the square metre” without calculating the thickness for each section.
  • Using water-based paint in an unheated building without a protective topcoat.
  • A topcoat that “happened to be in stock” instead of one tested as part of the system.
  • Application over a dusty or damp primer, or at temperatures below the permitted minimum.
  • No dry film thickness (DFT) checks: under-thickness at edges and corners.
  • Mechanical damage during erection that is never repaired.

Materials from leading manufacturers

  • Interchar 1120 — International (AkzoNobel) — single-component water-based paint for exposed steelwork inside buildings.
  • PPG STEELGUARD 651 — PPG — water-based thin-film paint for site application, including in occupied buildings.
  • PPG STEELGUARD 701 — PPG — solvent-based paint for shop and site application.
  • FIRETEX FX5090 — Sherwin-Williams — water-based thin-film paint for steel in dry interiors; with a topcoat, for more demanding conditions.
  • FIRETEX FX6002 — Sherwin-Williams — very fast-drying three-component coating for shop application.
  • Nullifire SC801 — Nullifire (Tremco CPG) — water-based thin-film paint for beams, columns and cellular beams.
  • Nullifire SC804 — Nullifire (Tremco CPG) — water-based paint optimised for medium ratings; also used on concrete.
  • Nullifire SC902 — Nullifire (Tremco CPG) — single-coat, high-build, fast-curing system for shop and site application.
  • Jotun SteelMaster 600WF, 900WF and 1200WF — Jotun — water-based thin-film paints optimised for 60, 90 and 120 minutes.
  • Jotun SteelMaster 60SB and 90SB — Jotun — solvent-borne acrylic paints for steel; fast-drying QD versions are available.
  • Jotun SteelMaster 1200HPE — Jotun — solvent-free epoxy intumescent coating, including for exterior conditions up to C5.
  • Interchar 963 — International (AkzoNobel) — single-pack solvent-borne acrylic paint for shop application.
  • HENSOTHERM 920 KS — Teknos — two-component solvent-free fire protection paint for internal and external use, R30–R120, ETA 21/0475.
  • HENSOTHERM 421 KS — Teknos — water-based fire protection paint for steel indoors, R15–R150 for open sections and up to R180 for hollow sections.
  • FIRETEX FX5120 — Sherwin-Williams — TCEP-free water-based thin-film coating for steel inside buildings, up to 120 minutes.
  • PPG STEELGUARD 550 — PPG — solvent-borne intumescent paint for shop and site application, up to 150 minutes.
  • PPG STEELGUARD 801 — PPG — fast-drying solvent-borne intumescent coating for shop and site fire protection of steel.
  • PPG STEELGUARD 851 — PPG — fast-drying solvent-borne intumescent coating, up to R120 for I-sections and hollow sections.
  • PPG STEELGUARD 751 — PPG — solvent-borne intumescent coating for steel, up to 1500 µm in one coat.
  • FIRETEX FX9502 — Sherwin-Williams — mesh-free epoxy intumescent coating for exposed steel inside and outside buildings.
  • FIRETEX FX7002 — Sherwin-Williams — single-component solvent-based acrylic paint for steel in dry interiors.
  • FIRETEX FX2002 — Sherwin-Williams — single-component solvent-based paint for shop application, assessed to EN 13381-8.
  • Interchar 2060 — International (AkzoNobel) — single-pack solvent-borne acrylic intumescent for steel, up to 60 minutes in one coat.
  • Interchar 404 — International (AkzoNobel) — CE-marked solvent-borne acrylic intumescent, up to 2 hours to EN 13381-8.
  • Interchar 1190 — International (AkzoNobel) — water-borne thin-film intumescent for on-site interior steelwork, up to 2 hours.
  • Nullifire SC803 — Nullifire (Tremco CPG) — water-based intumescent coating for dry, protected steelwork, optimised for 60 minutes.
  • Nullifire SC601 — Nullifire (Tremco CPG) — solvent-based intumescent coating for steel, applied on site or off site.
  • FIRETEX FX1003 — Sherwin-Williams — single-component solvent-based paint for on-site application, tested to BS 476.
  • Interchar 2090 — International (AkzoNobel) — single-pack solvent-borne acrylic intumescent for steel, up to 120 minutes.
  • Interchar 1260 — International (AkzoNobel) — water-borne intumescent for interior steel, up to 90 minutes, CE marked.
  • Interchar 1150 — International (AkzoNobel) — water-borne acrylic intumescent for interior steel, up to 2 hours to EN 13381-8.
  • PPG STEELGUARD 803 — PPG — fast-drying solvent-borne intumescent paint for I-section beams and columns, up to R45.
  • PPG STEELGUARD 864 — PPG — fast-drying solvent-borne intumescent paint, up to 120 minutes, tested to ASTM E119 and NCh-935.
  • FIRETEX FX1008 — Sherwin-Williams — fast-drying solvent-based intumescent paint for on-site application, up to 120 minutes to BS 476.
  • FIRETEX FX2008 — Sherwin-Williams — fast-drying solvent-based intumescent paint for shop application, up to 120 minutes to BS 476.
  • FIRETEX FX6010 — Sherwin-Williams — two-component ultra-fast-drying intumescent coating for steel, up to 120 minutes.
  • Jotun SteelMaster 120SB — Jotun — solvent-borne acrylic intumescent paint for steel, tested to BS 476 and GB 14907.
  • Jotun SteelMaster 90SB QD — Jotun — fast-drying solvent-borne acrylic intumescent paint for steel, up to 120 minutes.
  • Jotun SteelMaster 60SB QD — Jotun — fast-drying solvent-borne acrylic intumescent paint for steel, tested to BS 476.
  • Jotun SteelMaster 120WB — Jotun — water-based intumescent for beams, columns and hollow sections inside buildings, 60–120 minutes.
  • Jotun SteelMaster 60WB — Jotun — water-based thin-film intumescent for interior steel in environments up to C3.
  • PPG STEELGUARD 652 — PPG — water-based thin-film intumescent paint for interior steel, up to 120 minutes to UL 263.
  • Nullifire SC802 — Nullifire (Tremco CPG) — water-based intumescent coating for internal steelwork, up to 60 minutes.
  • Nullifire SC901 — Nullifire (Tremco CPG) — fast-curing two-component off-site intumescent for steel, up to 120 minutes in one coat.
  • CAFCO SprayFilm WB 3 / ISOLATEK Type WB 3 — Isolatek International — water-based intumescent coating for exposed interior steel, up to 4 hours.
  • PROMAPAINT-SC4 — Promat — water-based intumescent paint for steel I-sections and hollow sections.
  • Interchar 973 — International (AkzoNobel) — fast-drying solvent-borne acrylic intumescent for beams and columns, up to 2 hours.
  • Interchar 1160 — International (AkzoNobel) — water-borne intumescent for interior steel, up to 60 minutes to EN 13381-8, CE marked.
  • Interchar 1290 — International (AkzoNobel) — water-borne intumescent for interior hollow steel sections, tested to BS 476.
  • FIRETEX Platinum — Sherwin-Williams — solvent-free epoxy intumescent for steel up to R90 with C5 corrosion protection.
  • Unitherm Steel WB-120 — Sherwin-Williams — fast-drying water-based intumescent for interior steel, R15–R120 to EN 13501-2.
  • FIRETEX FX1007 — Sherwin-Williams — single-pack solvent-based intumescent for on-site application, up to 60 minutes to EN 13381-8.
  • Pyroplast ST-100 — Sherwin-Williams — water-based intumescent for interior steel, up to 90 minutes, DIN 4102-2 approval.
  • Nullifire SC604 — Nullifire (Tremco CPG) — off-site solvent-based intumescent for steel, up to 60 minutes, CE to ETA 21/0683.
  • CAFCO SprayFilm WB 7 / ISOLATEK Type WB 7 — Isolatek International — water-based intumescent for interior steel, up to 2 hours to BS 476.
  • Protecta Steel Paint FR-1 — Protecta (Polyseam) — water-based intumescent paint for interior structural steel, R30–R60 to EN 13381-8.
  • Protecta Steel Paint FR-120 — Protecta (Polyseam) — water-based intumescent paint for interior structural steel, up to R120 to EN 13381-8.

This list is not exhaustive. The final choice is made on the basis of the manufacturer’s documents and the project requirements.

Frequently asked questions

Can water-based paint be applied in winter?

Only in a heated space, and only if the minimum air and steel temperatures stated in the technical data sheet are maintained. Cold and humidity slow drying dramatically, and a coat applied in unsuitable conditions may never develop the required properties.

Is a topcoat needed?

In dry interiors, many water-based paints can be left without a topcoat. In unheated buildings, at elevated humidity or where a decorative finish is required, a topcoat is needed — and it must be one that is compatible with the fire protection.

How many coats should be applied?

That depends on the required dry film thickness and how much the particular product can build in a single pass. The number of coats is specified by the manufacturer; the key point is to achieve the design thickness over the entire surface, including edges.

What are the advantages of paint over plaster?

Paint is thinner and lighter and preserves the architectural appearance of the steel. Plaster is usually more cost-effective at high fire resistance ratings and more resistant to impact. Both solutions are often used on the same project.