Sprayed fire-resistive materials, bond strength, and the IBC

by CS Editor | February 5, 2014 10:32 am

by John Dalton
Sprayed fire-resistive materials (SFRMs) are passive fire-protection materials intended for direct application to structural building members. They are predominantly cementitious or mineral-fiber-based, with the fire-resistive qualities and physical characteristics varying widely between the respective types. A recent code change pertaining to these materials is important for design/construction professionals to understand.

Fire resistance of the assemblies to which the SFRM are applied are measured and defined by fire endurance tests such as ASTM E119, Standard Test Methods for Fire Tests of Building Construction and Materials. Physical characteristics are determined in accordance with ASTM E605, Standard Test Methods for Thickness and Density of Sprayed Fire-resistive Material Applied to Structural Members, and ASTM E736, Standard Test Method for Cohesion/Adhesion of Sprayed Fire-resistive Materials Applied to Structural Members, among others.¹

In 2009, the International Building Code (IBC) was changed to include higher bond strength requirements for SFRMs; this bond strength is based on the height of the building. As a consequence, the code change has an impact on the selection process of SFRMs for projects being constructed that were permitted under the 2009 or later version of the code.

The IBC lists three physical properties for SFRMs:

• thickness of application;
• density in pounds per cubic foot; and
• bond strength (adhesion/cohesion).

Of these three physical properties, only bond strength has requirements specifically outlined by the code. In the case of application thickness and density, the code states these properties must meet the requirements of the approved fire resistance design. These properties require special inspection as required in IBC Chapter 17.

In the 2009 IBC, the bond strength requirements changed for SFRM in response to the recommendations made by the International Code Council’s (ICC’s) Ad-hoc Committee on Terrorism Resistant Buildings (TRB) proposals. The committee studied the National Institute of Standards and Technology (NIST) reports and made recommendations based on the World Trade Center attack documents. In the reports, NIST recommended an increased bond strength requirement for “high-rise buildings,” which are defined in Chapter 2 of the IBC as those with an occupied floor located more than 23 m (75 ft) above the lowest level of fire department vehicle access.

Before 2009, IBC required the bond strength of SFRM—when tested in accordance with ASTM E736,—to be in excess of 7.18 kPa (150 psf). In 2009, IBC moved away from a single value for the bond strength of SFRM for all buildings, and implemented bond strength requirements based on the building’s height. The code maintained the 7.18-kPa bond strength demand for buildings with a height of less than 22.9 m (75 ft), while increasing bond strength requirements for taller buildings. In fact, IBC added two new bond strength requirements by segmenting buildings in categories of 22.9 m to 128 m (420 ft), and taller.

The minimum bond strength for SFRM for buildings greater than 22.9 m above the lowest level of fire department vehicle access is provided in the 2009 IBC in Section 403, “High-rise Buildings,” while the minimum bond strength of 7.18 kPa for SFRM of buildings below that height is stated in Section 1704.12.6, “Bond Strength of SFRM.” These requirements are detailed in the chart and schematic below.[1] [2]

(It must be noted the minimum bond strength requirement for the SFRM must be installed throughout the building.)

The specification community will need to consider these bond strength requirements when specifying SFRM on any projects designed under the 2009 IBC or later edition. Plan reviewers also need to keep this in mind as they review construction documents during the permitting process.

Though the new code must be considered when developing criteria for bond strength in a specification, the new bond strength requirements have no impact on any other physical property criteria for the SFRM in a specification.

For example, the new code language has no impact on density requirements. The selection of density criteria is an independent decision to the required minimum bond strength as dictated by the 2009 IBC. Traditionally, SFRMs have been divided into three distinct product groupings based on their density. There were:

• low-, standard-, or commercial-density (i.e. 240 to 336 kg/m³ [15 to 21 pcf])—usually containing a gypsum binder;
• medium-density (350 to 625 kg/m³ [22 to 39 pcf])—usually contains a cement and/or gypsum binder; and
• high-density (more than 625 kg/m³)—containing a cement binder.

Historically, there is a relationship between the applied cost of SFRM and the increase in density. The cost difference is driven primarily by the applied yield of the materials. As density increases, the applied yield of the material decreases and applied cost increases. Some have also attempted to correlate bond strength with cost, but the same correlation does not exist.

Until recently, the only way to meet the new code requirements was to specify a medium-density SFRM product. This is because the market had lacked low-density products that could achieve bond strengths in excess of 20.6 kPa (430 psf). As a result, medium-density products are being specified in applications where a standard density product would meet all the requirements with the exception of bond strength. A prime example of this is when the SFRM is to be concealed once the building is complete in those structures taller than 22.9 m.

This practice has created the misconception medium-density SFRMs must be specified to meet the new building code high-rise building requirements. This is no longer the case. Over the last year, several new low-density products can achieve the required high-rise bond strength requirements. The introduction of these products has created more cost-effective solutions to meeting IBC bond strength requirements.

These low-density SFRMs typically provide higher yields, and faster application/coverage rates when compared with medium-density products, offering lower in-place cost solutions. Using these such products offers significant advantages to the building owner and manager.

Prior to the new bond requirement, designers must consider several factors when selecting the appropriate SFRM for a project:

• Will the SFRM be for interior or exterior applications?
• Will the SFRM be concealed or exposed?
• Will the SFRM be merely exposed to view, or will it experience abrasion?
• If exposed to abrasion, what is the anticipated level?
• Does the SFRM need to be damage-resistant?
• Will the SFRM be exposed to high humidity?

Now, for buildings being designed in accordance to the 2009 or later version of the IBC, the following question must also be added:

• How tall will the building be?

With the introduction of the new high-bond, low-density products, the design has more flexibility in selecting the products meeting all requirements versus choosing a product that meets the new bond requirements, but exceeds all the others at a higher cost.

Notes
¹ An earlier version of this author’s article appeared as “Significant Changes to Bond Strength Requirements in the 2009 IBC,” which appeared in the Fall/Winter 2013 edition of Life Safety Digest, published by the Firestop Contractors International Association (FCIA).

John Dalton is technical service manager of fire protection at Grace Construction Products. He has more than a decade of experience in the industry, providing technical assistance to architects, building officials, and contractors in the fireproofing area. Dalton can be reached john.a.dalton@grace.com[3].

Source URL: https://www.constructionspecifier.com/sprayed-fire-resistive-materials-bond-strength-and-the-ibc/

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