Fireproofing: Types (SFRM, Intumescent, Firestop), Fire Ratings and Selection

Fireproofing is passive fire protection in 3 product classes, sprayed fire-resistive materials (SFRM), intumescent coatings and firestop sealants, that keep structural steel below its failure temperature and stop fire passing through openings in rated walls and floors. Each class earns a rating only as part of a tested and listed design, so which one fits which structure?

The 3 classes fall into 2 groups: structural fire protection for steel (SFRM and intumescent coatings) and compartmentation seals (firestop sealants and penetration seals). UK specifiers call the whole field passive fire protection (PFP) and the sealing of openings "fire stopping". Fireproofing is one of the 15 families of construction chemicals.

Ratings run from 1/2 to 4 hours under ASTM E119-26 and UL 263 and from R 15 to R 240 under EN 13501-2:2023, while UL 1709 tests hydrocarbon fires that reach 1,093 °C (2,000 °F) within 5 minutes. VOC limits run from 150 g/L (1.25 lb/gal) to 450 g/L (3.8 lb/gal).

Standards, codes and regulations are checked against their issuing bodies, product values against the named data sheet and prices against the dated source named in the sentence; see our methodology and fact-checking.

What Is Fireproofing?#

Fireproofing is a passive fire protection layer or seal, applied to structural members or into openings, that holds a tested fire-resistance rating of up to 4 hours without any activation by people, power or water.

The purpose of fireproofing is to keep the structure load-bearing and the fire compartments closed long enough for evacuation and firefighting. UL 263 and ASTM E119-26 put that purpose in numbers: a protected steel column reaches its limit at an average steel temperature of 538 °C (1,000 °F). A product proves this only inside a tested design, so the same coating on a lighter section carries no rating.

Passive vs active fire protection#

Passive fire protection is built into the structure and needs no activation, while active fire protection, such as sprinklers and alarms, has to detect or respond to a fire. Fireproofing belongs to the passive type only: it is one part of fire protection, not a synonym for it. Fireproofing materials, fireproofing coatings and structural fire protection are other names for it.

How Does Fireproofing Work?#

Fireproofing works in 3 ways: SFRM insulates steel with a low-conductivity, water-bearing layer, intumescent coatings swell into an insulating char when heated, and firestop sealants fill and seal openings in a listed system. None of the 3 carries a rating outside the tested assembly it was listed in.

Insulating and heat-absorbing layers#

SFRM keeps steel below its limiting temperature with a thick, low-conductivity layer of gypsum- or cement-bound fibers and lightweight aggregates. The gypsum and cement hydrates absorb heat while they release bound water.

The rating of an SFRM layer depends on 3 values in the listed design: thickness, density and the W/D of the steel section. SFRM arrives as a powder mixed with water (wet-mix) or as a dry-mix fiber wetted at the nozzle, and gypsum binders are described under calcium sulfate binders.

Intumescent char formation#

An intumescent coating stays a thin film until heated, then the binder melts and a blowing agent foams it into a carbon char that insulates the steel. The word intumescent means swelling up.

Thin-film coatings carry 3 active ingredients in a thermoplastic binder (acrylic, vinyl or PVA): ammonium polyphosphate (acid source), pentaerythritol (carbon source) and melamine (blowing agent). The acid esterifies the carbon source while melamine gas foams the melt. Thick-film coatings are 2-component epoxies at 100 % solids.

The char needs room to expand, so the manufacturer states the clearance, and char strength caps the maximum thickness. Thin-film binders are covered under acrylic polymers.

Sealing openings to hold fire compartments#

A firestop sealant fills the annular space around a pipe, cable or duct, or a joint, together with a forming material such as mineral wool, to stop flame, hot gas and smoke. Three chemistries do this work: water-based acrylic, latex with intumescent and endothermic fillers, and neutral-cure silicone. Intumescent grades close the void left when a plastic pipe burns away, and endothermic fillers absorb heat. Sealant depth comes from the listing, never from the width-to-depth rule used for building joints.

3 Types of Fireproofing in 2 Groups#

The 3 types of fireproofing fall into 2 groups: structural fire protection for steel (SFRM and intumescent coatings) and compartmentation seals (firestop sealants and penetration seals). Spray fireproofing is called SFRM, or spray-applied, cementitious or spray-on fireproofing. The table below compares the 2 groups by class, mechanism and the documents that rate them.

1. Structural fire protection for steel (2)#

Structural fire protection for steel insulates beams, columns and floor deck so they stay load-bearing for the rated time; this group has 2 classes: SFRM and intumescent coatings.

Sprayed fire-resistive materials (SFRM)#

Sprayed fire-resistive materials are gypsum- or Portland cement-bound sprays with fibers and lightweight aggregates, applied in thick layers to steel. They are listed as UL category CHPX materials in UL 263 designs and tested in Europe to EN 13381-4:2013, with CE marking through EAD 350140-00-1106. Concealed members are their main use; tunnel and concrete protection is a section of the SFRM page.

Intumescent coatings, thin-film and epoxy#

Intumescent coatings are reactive films that stay thin until a fire and then swell into char. Thin-film grades are UL category CDWZ materials in UL 263 designs, epoxy grades add UL 1709 hydrocarbon listings, and Europe tests both to EN 13381-8:2013 with CE marking through EAD 350402-00-1106. Timber and mass-timber grades are a section of the intumescent page.

2. Compartmentation seals (1)#

Compartmentation seals keep fire, hot gas and smoke inside the compartment where a fire starts; this group has 1 class: firestop sealants and penetration seals. They restore the rating of a wall or floor that a pipe, cable, duct or joint has breached.

Firestop sealants and penetration seals#

Firestop sealants and penetration seals are acrylic, intumescent latex or silicone sealants installed with forming material as part of a listed system. US systems are tested to ASTM E814-26 for penetrations and ASTM E1966-24 for joints; EU seals are tested to EN 1366-3:2021+A1:2024 and EN 1366-4:2021 and CE marked through EAD 350454-00-1104 or 350141-00-1106. Boards, mats and wraps (UL categories CERZ and CEAV) are non-chemical alternatives and are not counted here.

Intumescent vs Cementitious Fireproofing: How the Types Compare#

Intumescent and cementitious fireproofing reach the same UL 263 ratings on the same steel members, but SFRM insulates by thickness and mass while an intumescent film expands in fire, which changes finish, exposure and inspection. The table below compares SFRM with thin-film and epoxy intumescents across 10 attributes.

SFRM density classes of 240 to 336, 352 to 625 and above 625 kg/m³ (15 to 21, 22 to 39 and above 39 pcf) are an industry convention, not a code class.

Intumescent vs cementitious fireproofing#

Cementitious SFRM suits concealed beams, columns and deck, while intumescent coatings suit exposed and architectural steel that needs a paint-like finish. Epoxy intumescents and high-density SFRM cover the hydrocarbon and exterior end of the range.

Inspection differs as much as the finish. SFRM is checked for thickness and density by ASTM E605/E605M-19(2023) and for bond by ASTM E736/E736M-19(2023), while an intumescent is checked for dry film thickness (DFT) within the listed minimum and maximum. SFRM topcoats add color only; an intumescent topcoat is a certified UL XKXC2 component wherever the listing requires one, and always outdoors.

Installed costs of USD 53.82 to 96.88 per m² (USD 5 to 9 per ft²) for 15 pcf SFRM compare with USD 64.58 to 150.70 per m² (USD 6 to 14 per ft²) for water-based thin-film intumescent (installed, US TX/KS/OK, Bahl contractor cost guide, 2026-04; the source gives no rating split). Intumescents go over blast-cleaned, primed steel, and water-based grades need a dry internal environment without condensation; blast grades for steel are set out under steel surface preparation grades.

Fireproofing vs firestopping#

Fireproofing protects structural members, while firestopping seals openings and joints in rated walls and floors so fire and smoke stay in their compartment. A fireproofed beam carries no rating for the wall it passes through, and a firestop system carries none for the beam.

Fireproofing is rated in UL 263 and ASTM E119-26 designs; firestopping is rated to ASTM E814-26 and UL 1479 for penetrations and to ASTM E1966-24 and UL 2079 for joints. ASTM E814-26 gives an F rating (flame passage, plus a hose stream) and a T rating (a 181 °C (325 °F) point rise on the unexposed side), and UL 1479 adds L (air leakage) and W (water) ratings.

Elastomeric acrylic and silicone firestop grades take joint movement, which UL 2079 tests by cycling before the fire test, while non-rated joints are sealed with construction sealants.

Where Is Fireproofing Used? Selection by Structure and Exposure#

Fireproofing is used on 4 structure types (steel-framed buildings, exposed architectural steel, hydrocarbon-fire facilities, and the penetrations and joints of rated walls and floors), and the fire curve and exposure at each one set the class. Tunnel and concrete protection is a section of the SFRM page, and timber grades a section of the intumescent page. The table below matches each structure to its exposure, classes and deciding rule.

Steel-framed buildings: beams, columns and floor deck#

Concealed beams, columns and steel floor deck in commercial buildings take SFRM or thin-film intumescent, applied to the thickness and density the listed design gives for each member. UL designs mark the protection type in the first digit: D700-series floor-ceiling designs use SFRM, and D600-series designs use intumescent coatings. IBC 2024 Section 704.12 (704.13 in IBC 2021) requires SFRM to be installed per its listing and the manufacturer's instructions.

Exposed and architectural steel#

Exposed steel takes thin-film intumescent coatings, with a certified UL XKXC2 topcoat wherever the listing requires one and always outdoors. Exterior and humid locations need a grade whose listing or EAD exposure type covers them. Cladding fixed tight to the member blocks the expansion of the char.

Petrochemical, energy and other hydrocarbon-fire facilities#

Plants exposed to hydrocarbon pool fires take epoxy intumescents or high-density cementitious systems tested to UL 1709, which reaches 1,093 °C (2,000 °F) within 5 minutes. Every UL 1709 product also passes UL 2431 durability testing, and its category, from I-A (outdoor heavy industrial) to II-A-3 (indoor exposed, non-controlled), has to match the location. Mesh goes in wherever the listing calls for it.

Penetrations and joints in rated walls and floors#

Every pipe, cable or duct through a rated wall or floor needs a firestop system with an F rating, and some floor penetrations also need a T rating. Head-of-wall and other joints take joint systems tested to ASTM E1966-24, and curtain wall slab edges take perimeter fire barriers tested to ASTM E2307-25b.

Which Fire Ratings and Standards Govern Fireproofing Products?#

Fireproofing products are governed in 3 layers: fire tests that set the rating, listings or assessments that tie a product to a design, and code inspection of the applied work. In the US these are ASTM E119-26 and UL 263, the UL directory and IBC 2024 Sections 1705.15 and 1705.16; in Europe, EN 13381 tests feed EN 13501-2:2023 classes and a European Technical Assessment (ETA).

How fire-resistance ratings are tested#

UL 263 and ASTM E119-26 expose a loaded or instrumented member to a furnace that reaches 538 °C (1,000 °F) at 5 minutes and 1,093 °C (2,000 °F) at 4 hours, giving ratings from 1/2 to 4 hours. ANSI/UL 263 (14th edition, 2011-06-21, last revised 2025-09-02) is technically equivalent to ASTM E119 and to CAN/ULC-S101 in Canada, and NFPA 251 is withdrawn.

Steel limiting temperatures are 538 °C (1,000 °F) average and 649 °C (1,200 °F) at a point for columns, and 593 °C (1,100 °F) and 704 °C (1,300 °F) for beams. Test criteria and design numbers are explained under UL 263 and ASTM E119.

Listed designs, steel section factor (W/D) and applied thickness#

A fireproofing thickness is read from the listed design for the member's weight-to-heated-perimeter ratio (W/D), and steel lighter than the listed size never takes the listed thickness. An equal or greater W/D may use the listed thickness, so upsizing steel can reduce it.

An intumescent average DFT never exceeds the listed maximum. Attached steel takes a coatback of 450 mm (18 in) where its cross-section exceeds 3,000 mm² (4.65 in²) per m (per 3 ft) (UL Solutions guide, 2022); UK guidance (ASFP TGD 8) sets 500 mm where no evidence supports omission.

IBC 2024 Section 1705.15 calls for special inspection of SFRM per AWCI 12-A-2017, with a field bond strength of at least 7.18 kPa (150 psf) by ASTM E736, and Section 1705.16 covers intumescent fire-resistive materials per AWCI 12-B-2014. Sampling and acceptance are set out under fireproofing inspection.

Rapid-rise fires and exterior durability: UL 1709 and UL 2431#

UL 1709 (6th edition, 2022-08-08, revised 2024-07-08) rates hydrocarbon fireproofing against a fire that reaches 1,093 °C (2,000 °F) within 5 minutes, and every UL 1709 product also passes UL 2431 durability testing. UL 2431 sorts exposure into 5 categories, listed below.

• I-A: outdoor, heavy industrial.
• I-B: outdoor, general.
• II-A-1: indoor, concealed, controlled environment.
• II-A-2: indoor, concealed, elevator shafts.
• II-A-3: indoor, exposed, non-controlled environment.

UL lists these products in category BYFH, and ASTM E1529-22 defines a large hydrocarbon pool fire by heat flux.

European and UK routes: EN 13381, EN 13501-2, EADs and the Yellow Book#

European fireproofing is tested to EN 13381-4:2013 (passive protection such as SFRM) or EN 13381-8:2013 (reactive coatings), classified R 15 to R 240 under EN 13501-2:2023, and CE marked through a European Technical Assessment. No harmonized product standard exists, and a UL 263 listing cannot replace an EN 13381 assessment.

EAD 350402-00-1106 assesses reactive coatings for 4 exposure types: X (all climates), Y (internal and semi-exposed), Z1 (internal, relative humidity 85 % or more) and Z2 (internal, below 85 %). Firestop seals are classified E or EI in minutes.

The UK keeps BS 476-20/21 with the ASFP Yellow Book Rev 6 Vol 1 (January 2025), which set default critical temperatures of 500 °C (932 °F) for columns and 580 °C (1,076 °F) for 3-sided beams. ETA and DoP rules are set out under EU Construction Products Regulation.

VOC Limits and Safety Rules for Fireproofing Products#

VOC limits for fireproofing depend on jurisdiction and category, from 150 g/L (1.25 lb/gal) for fire-proofing coatings in the South Coast air district to 450 g/L (3.8 lb/gal) for opaque fire-resistive coatings under the federal EPA rule. Safety rules add 3 checks for applicators: the melamine and epoxy classifications, REACH diisocyanate training, and cement and dust controls.

VOC limits by jurisdiction#

SCAQMD Rule 1113 (amended 2016-02-05) limits Fire-Proofing Coatings, opaque coatings UL-listed to protect structural steel, to 150 g/L (1.25 lb/gal). The federal EPA AIM rule (40 CFR 59 subpart D) sets 450 g/L (3.8 lb/gal) opaque and 850 g/L (7.1 lb/gal) clear for coatings made on or after 1999-09-13.

Firestop sealants have no category of their own in SCAQMD Rule 1168 (amended 2022-11-04) and fall under All Other Architectural Sealants at 50 g/L (0.42 lb/gal); every category is listed under VOC limits for construction chemicals.

Inorganic SFRM is essentially VOC-free. The table below compares the limits in g/L (lb/gal), EU Directive 2004/42/EC included.

Melamine, epoxy, diisocyanate, cement and dust rules for applicators#

Melamine, the blowing agent in thin-film intumescents, carries the classification "Harmonised CLP Annex VI (index 613-345-00-2, ATP18): H351, H373", applicable since 2023-11-23, and has been on the REACH Candidate List since 2023-01-17.

Epoxy intumescents carry the liquid epoxy resin classification "Harmonised CLP Annex VI (index 603-074-00-8): H315, H317, H319, H411"; for the hardeners, see the product SDS. REACH Annex XVII entry 74 requires training since 2023-08-24, renewed at least every 5 years, for products with 0.1 % by weight or more diisocyanates; here that means polyurethane topcoats and polyurethane foam firestop products only. Hazards of epoxy resins are set out on their material page.

Cement-based SFRM carries the Portland cement line "No Annex VI entry; ECHA C&L notified classification: H315, H317, H318, H335"; see the product SDS. Where the SDS lists crystalline silica, OSHA 29 CFR 1926.1153 (effective 2016-06-23) applies, with a PEL of 50 µg/m³ and an action level of 25 µg/m³ (8-hour TWA).

Complete List of Fireproofing Product Classes: All 3 Classes#

The complete list below gives all 3 fireproofing product classes with their chemistry, US and European standards, use, applicator need and a dated installed cost where one is published.

UL 1479, UL 2079 and UL 2431 are shown without an edition; boards, mats and wraps (UL CERZ and CEAV) are not listed.

Structural steel PFP accounts for 0 to 1.2 % of total construction cost (share, Journal of Constructional Steel Research 2024, quoted by the Bahl contractor cost guide, US, 2026-04). Prices by rating are compared under fireproofing cost per square foot.

Which Type of Fireproofing Is Right for a Project?#

No fireproofing type is right for every project: the right class is the one listed for the member size, rating, exposure and finish, and a specification names it by design number and standard, not by brand. A concealed beam can take SFRM in a D700-series design, and a refinery pipe rack an epoxy intumescent with a UL 1709 listing and a UL 2431 category.

Does structural steel need to be fireproofed?#

Structural steel needs fireproofing where the building design assigns its members an hourly fire-resistance rating, and the rating is proven by a tested UL 263 or ASTM E119-26 design. The material, thickness and inspection then follow that design.

Is fire-retardant paint the same as fireproofing?#

No: a fire-retardant paint tested for surface burning to ASTM E84 slows flame spread on wood or finishes, but a surface-burning result never satisfies a fire-resistance rating. Thermal and ignition barrier coatings over spray polyurethane foam form a separate category (IBC Section 2603, ICC-ES AC377).

Can intumescent and cementitious fireproofing meet on one member?#

Only where a tested design covers the transition: engineering judgments are not a substitute for tested designs and are used only after the search for one is exhausted. A drawing that shows both materials on one member therefore cites the design or the judgment for the joint between them.

How long does fireproofing last?#

EAD 350402 assesses reactive coatings for an assumed working life of 10 years, or 25 years with documented proof, which is an assessment basis, not a guarantee. Site service life also depends on exposure type, topcoat and damage by later trades.

Does fireproofing contain asbestos?#

No: current SFRM formulations are asbestos-free, though mixing and spraying still create dust that the product SDS addresses. Respiratory and eye protection for that dust come from the product SDS.