Mastic and Intumescent Coatings

Authored by: Luke C. Woods, Principal Engineer - Fire Resistance and Containment and Bruce E. Johnson, Regulatory Services Regional Manager

Model building codes rely on passive and active fire protection products and systems to safeguard people from fire and other hazards. These systems help protect firefighters and emergency responders during emergency operations by maintaining the passive fire protection system(s) and structural integrity of the building during a fire event.

The overall passive fire protection in a building provides a compartment for containing fire and smoke. This compartment is constructed with fire-resistance-rated fire walls, fire barriers, fire partitions, smoke barriers, shaft enclosures and horizontal fire-rated assemblies as well as complementary active fire protective systems to control or limit the spread of fire. Fire-resistance ratings may be determined in accordance with ASTM E119 or UL 263, Fire Tests of Building Construction and Materials, to establish the fire exposure time period, expressed as an hourly-rating.

Several methods can be used to determine the compliance of fire resistance-rated construction with model building codes including:

• Fire-resistance designs documented in approved sources.
• Approved prescriptive construction methods or performance-based calculations.
• Engineering analysis based on documentation as determined by the test procedures in ASTM E119 or UL 263.
• Alternative materials and methods as allowed by a model building code.

An important aspect of building fire safety is maintaining structural integrity by protecting the structural elements used to support the floors, walls, roofs and other functional systems of a building. Various products are used to protect the structural elements such as boards, wraps, cementitious or fibrous sprays and intumescent and mastic coatings. Some of these materials have reactive properties that provide an increased level of insulation when exposed to elevated temperatures.

Fire-resistive coating materials

Coating materials used to protect structural building elements include products identified as either spray-applied fire-resistive materials (SFRM) or intumescent fire-resistive materials. Spray-applied fire-resistive materials are applied at specified densities and thicknesses to structural members to provide thermal insulation that ensures the structural member retains the required structural and load-bearing capability and does not exceed the critical elevated temperature as specified in ASTM E119 or UL 263.

Mastic and intumescent coatings are relatively thin, paint-like coatings that have a reactive chemistry resulting in expansion at elevated temperatures. Typical coating application thickness is between 0.03 and 0.50 inches; these materials will typically expand approximately 15 to 30 times their original size when tested in accordance with ASTM E119 or UL 263. As these coatings expand when exposed to fire, they create a thermal insulating material that ensures the protected structural member retains its required structural and load-bearing capability and does not exceed critical elevated temperatures as specified by ASTM E119 or UL 263.

Ensuring code compliance

The model building codes, product certification details and product manufacturer’s instructions all include important information for the use of these materials in fire-resistance-rated construction. Failure to adhere to all the requirements and instructions within a product or system certification may significantly inhibit the ability of these materials to provide the required fire protection for structural building elements.

The key model code requirements and certification information include:

• The structural element (beam, joist, column, roof assembly or floor-ceiling assembly) surface must be properly prepared for the material application. Primers are typically required and must be as specified in accordance with the product certification. Primers for structural steel are covered by UL product category CGJM.
• Galvanization of the underlying building element may impact the adhesion of spray-applied fire-resistive materials or intumescent coatings. Application over galvanized steel must be permitted by the certification.
• The coating materials must be applied during the environmental conditions defined by the manufacturer, e.g., low or high temperature, humidity, etc., using the specified method of application, with adequate ventilation and drying time described in the manufacturer’s instructions.
• Material application thickness and coverage must be within tolerances specified in the certification.
• Different materials are not permitted to be mixed or applied to the same surfaces unless otherwise noted in the individual certifications.
• The finished application cannot exhibit cracks, voids, spalls, delamination or any exposure of the underlying building elements.
• Some building types require special inspectors be present during the application process.

UL Certification for fire-resistive coatings

The UL guide information for fire-resistance ratings, BXUV, contains a great deal of additional information specific to fire resistance-rated coatings, SFRM and mastic and intumescent coatings that are applicable to all UL designs that include these coatings.

UL certifies a wide range of products that are covered by steelwork protective requirements in building codes. Spray-applied and intumescent and mastic coatings that have been certified by UL can be found in UL Product iQ^TM. Product iQ is free to use, but does require a one-time registration. These products and materials, and the applications for which they are certified, include spray-applied fire-resistive materials (CHPX) and intumescent fire-resistive materials (CDWZ).

To obtain a UL Certification, intumescent and mastic coatings must also demonstrate fire resistance performance after being subjected to several simulated environmental conditions based upon the area of installation, e.g., interior conditioned space, interior general purpose, exterior, etc. These conditions may include a combination of accelerated aging, elevated humidity, carbon dioxide and sulfur dioxide air mixture, salt spray, ultraviolet light, freezing and simulated rain for coatings intended for outside exposure. After samples, typically 2 feet in length, are conditioned by the simulated environments, the samples are subjected to the furnace fire test specified by ASTM E119 or UL 263. These additional environmental condition tests are essential because some intumescent and mastic coatings are extremely sensitive to moisture where such exposure could significantly reduce fire-resistance performance.

UL recognized designs (Certifications) include tables that specify thickness of intumescent and mastic coatings for various steel shapes to achieve required hourly fire resistance-ratings. The BXUV guide information includes equations for SFRM thickness adjustments as a function of the size and the mass of a steel building element. It is important to note that these general equations do not apply to intumescent or mastic coatings because of the different characteristics of these coating materials.

UL Certification Mark

The presence of a UL Certification Mark on the packaging of fire-resistive intumescent and mastic coatings or SFRMs is essential because it is the only method to identify the materials are manufactured in compliance with the UL requirements that include BOTH fire test performance and product performance. These products are eligible to carry either the UL Enhanced Certification Mark or the UL Classification Mark. The presence of either of these Marks indicates that the material was manufactured under a required Follow-Up Service program, as required by the definition of “listed” in the model building codes. The purpose of Follow-Up Services is to determine ongoing compliance with requirements.  Additional information can be found in the UL Best Practice Guide for Passive Fire Protection for Structural Steelwork.