FROM THE FOUNDATION Primers Beneath Fire-Resistant Coatings by Douglas Jones, Southern Coatings, Inc. Active rusting and damaged mill scale on structural steel immediately before fireproofing Fig. 1 Reprinted by permission from IREPROOFING IS APPLIED Journal of Protective Coatings & to steel in commercial and indus- Linings. F trial structures to reduce the rate of temperature increase of the steel dur- About the Author: Douglas M. ing a fire. The thermal mass of the Jones is Research-Engineering Services fireproofing tends to prevent the con- Manager of the Corrosion Control centration of heat applied to structural Group of Southern Coatings, members and thereby gives firefighters Incorporated. time to battle the blaze before total With more than 10 years experience destruction results or before the struc- in the high performance protective ture collapses, with the attendant results coatings industry, Mr. Jones has been of injury and death. with Southern Coatings for three years This paper reviews the arguments for where his responsibilities include con- and against the use of primers beneath ducting on-site inspections and fireproofing, and takes the position that specification writing. primers are required in circumstances Mr. Jones has a B.S. in Chemistry where normal atmospheric corrosion is from the University of Louisville. He accelerated. Issues important to the currently serves as Chairman of the argument are construction practices, Primers Beneath Fireproofing Commit- adhesion of the fireproofing material to tee of the Steel Structures Painting the primers, and in-service exposure council. environments. Construction Dimensions/June 1989 37 Fire Resistant Coatings to application of a fire-resistant coating. Construction While some manufacturers of fire- Practices for resistant material prefer a Near-White Blast Cleaning (SSPC-SP 10) or a Commercial Commercial Blast Cleaning (SSPC-SP Buildings 6) in the shop, they are satisfied if the steel is lightly rusted at the construction For many fireproofing materials used site, and consider the condition of light in commercial buildings, such as some rusting to be ideal for application of in the categories of dense and fireproofing so that the appropriate lightweight concrete and cementitious, adhesion will result. surface preparation requirements are It must be taken into account, minimal. Typical requirements are however, what the conditions of removal of oil, grease, loose millscale, transport and storage will be for the dirt, and other foreign substances. The structural steel after it leaves the Underwriters Laboratories’ (UL) Fire fabricator’s shop and before it is erected Resistance Directory indicates that un- and fireproofed. Any number of primed steel should be “clean and free scenarios are possible, depending upon of dirt, loose millscale, and oil” prior weather, time of year, the geography, but the following are certainly en- countered on a regular basis. • The fabricated steel, shipped in winter on roads covered with deicing salts, is splashed with roadway slush and contaminated with chlorides. • The steel is delivered to and stored in a seacoast environment where chlorides again contaminate the surfaces. • In a heavy industrial environment, such as near chemical or other process plants, chlorides and sulfates are deposited on stored steel. • In areas of heavy acid rain deposi- tion, the transported and stored steel is contaminated by chemicals. • Steel is stored for extended dura- tions in the fabricator’s yard and/or at the construction site and suffers exten- sive rusting and damage to millscale. • Steel is randomly stacked, stacked close to or on the ground, or stacked so that water ponding occurs, with the result that corrosion and pitting take place. No matter what the conditions of storage, weather, contamination, or jobsite delay, they tend not to be predictable, and therefore planning on the basis of worst case scenarios is in order. Figure 1-3 show the results of some of these conditions. Presuming the worst case in con- 38 June 1989/Construction Dimensions, Fire Resistant Coatings struction practices as described above, (top) Fabricated steel erected structural steel before applia- has slivers that, tion of fireproofing is likely to be without blast cleaning, will become unevenly corroded and to have crack- sites for rusting. ing, flaking, or totally destroyed millscale if it has not been blast-cleaned. (bottom) Corrosion In addition, salt and other chemical on a beam in a contaminants may be present. fabricator's storage In such cases, once the fireproofing yard prior to is applied, even in the indoor en- shipment to the job vironments of commercial buildings, site. corrosion is likely to continue, having already established a strong electrolytic process, and having the capability to draw moisture from the water-based fireproofing. Only a very small amount of Fig. 2 moisture is required for active corrosion around millscale and where some pit- ting has already been initiated. This moisture is entrapped and available from the water-soaked fireproofing when it is applied. Fireproofing before it is enclosed also soaks up moisture from the weather. Even in an indoor environment, once a building has been enclosed, relative humidity in the range of 40 percent can make moisture available to steel through cracks in the fireproofing that develop from shrinkage, thermal fluc- tuation, or mechanical damage. If the corrosion process continues, a buildup of corrosion products can delaminate the fireproofing material. There have been instances when Fig. 3 fireproofing has delaminated from steel and thereby failed to protect a struc- ture during a fire. One documented ex- west section of the 33rd floor were ample is described in the New York twisted or deflected several inches and Board of Fire Underwriters’ report, the connecting bolts sheared off or fail- “One New York Plaza Fire.”2 The fire ed, allowing beams in some sections to occurred on August 5, 1970 in a rest on the flange of the girder.” 53-story building within a year of its On the 34th floor of the building, erection. “beams were severely deflected and Columns, girders, beams, and the distorted and the most severe structural underside of floors were protected by damage occurred in the west section of sprayed asbestos fiber fireproofing to this floor.” provide a four-hour fire resistance for The report concludes that “the columns and a three-hour rating for degree of damage to the steel frame is filler beams and floors. The report ad- the result of several factors. It is vises, in part, as follows: reported that this steel came from “Steel beams in the south center and England and became severely oxidized Construction Dimensions/June 198$ 39 Fire Resistant Coatings in transit. As a result the sprayed side of caution is more to be recom- asbestos fiber did not adhere well in mended than taking unnecessary risks. many places and fell off along with the The corrective action required to scale shortly after application.” assure that corrosion will not occur Further, the report states that “the beneath fireproofing is application of protection of steel members in a really a suitable primer in the fabricator’s fire-resistant building must be ac- shop under controlled conditions im- complished by materials that cannot be mediately after blast cleaning has taken readily removed or damaged. It is ap- place. parent . that proper adhesion to steel A rust-inhibitive primer can protect may not take place.” steel during shipping and storage, and The worst-case scenario, in which it can be easily cleaned before applica- steel is contaminated and actively tion of fireproofing material. rusting when fireproofing is applied, is not always going to take place, par- ticularly in extremely dry and otherwise Adhesion benign environments such as those One argument against the use of found in the Southwest. But where primers beneath fireproofing has been fireproofing is concerned, erring on the that the primed surface will not allow 40 June 1989/Construction Dimensions Fire Resistant Coatings fireproofing material to achieve a suf- ficient bond or adhesion to the surface. Testing Method #21 This position has been advanced by September 21; 1984 some manufacturers of fireproofing. Adhesion of Sprayed-On Fireproofing to Primers But laboratory test results show that 1. Scope fireproofing can achieve an adequate This procedure sets forth a method for determining the amount of force bond to primers. necessary to remove fireproofing material from a surface. My firm has conducted adhesion 2. Apparatus tests using our in-house Testing Method 2.1 Wal-Board Hopper Gun. foam insulation, 1 in. thick, metal caps 1¼ #21, “Adhesion of Sprayed-On in. dia., metal cup hooks, scale calibrated in ¼ in. increments to 30 lbs. max- Fireproofing to Primers.” (See boxed imum and a timer. item.) This Testing Method was 2.2 12 in. x 12 in. 16 gauge hot rolled steel panels or as specified. developed before the adoption of 2.3 Sprayed-on fireproofing material ASTM E 736, “Standard Test Method 3. Procedure 3.1 Clean steel panels with xylene and clean rags. Let the solvent evaporate for Cohesion/Adhesion of Sprayed and spray apply the primer to achieve the recommended dry film thickness Fire-Resistant Materials Applied to 3 DFT (normally 2 mils). After the primer has cured seven (7) days minimum, Structural Members,” and is similar in a 1 in. thick frame of styrene foam cut to an outside dimension of 12 in. x its procedures. 12 in. and inside dimension of 11 in. x 11 in. (for 12 in. x 12 in. hot rolled Procedures steel panels). This frame is glued to the primed panel with vinyl-acrylic emul- Five manufacturers of sprayed-on, sion (1535-AR). When completely set, the fireproofing material is sprayed-on waterbase fireproofing were listed in with the panel inside the frame using a Wal-Board Hopper Gun—with sprayed- on fireproofing mixed according to manufacturers’ instructions.