Fire Engineering

Construction Concerns: Sprayed-on Fireproofing


It has been known for nearly a hundred years that structural steel fails quickly when heated by fire. A short time later, building codes began to require protection of the structural steel in fire-resistive buildings, and rated the levels of protection as it did fire division walls (one-hour, two-hour, and so on).

The earliest forms of protection were to encase the steel columns and beams in terra-cotta (baked clay tile), concrete, or masonry. Later, gypsum plaster applied to wire lath was used, to reduce the weight of the fire protection. Multiple layers of gypsum drywall board were also used to reduce the labor required for installation. This method is still in use today.

Sprayed-on insulations were developed that could meet the Underwriters Laboratories (UL)/American Society for Testing and Materials (ASTM) fire rating tests, and became common after World War II. These materials were lightweight, provided the required heat resistance when tested in the laboratory, required less skilled labor to apply than masonry or plaster, and used asbestos fiber as the insulator and Portland cement or glue as binders.

In the 1970s, asbestos became a health concern, and was replaced in fireproofing by mineral wool and fiberglass. There is still a lot of asbestos out there in our buildings, so gross decontamination by low-pressure hoseline before removing SCBA or other personal protective equipment after interior firefighting is essential.

All sprayed-on fireproofing is not created equal. Those containing Portland cement or other inorganic binders seem more resistant to removal by fire hose streams than other types. The quality of the finished insulation depends on the cleanliness of the surface to which it is applied; the use of the right amount of water in the mixture; and the use of the correct air pressure while spraying.

Photo 1

Photo 1 shows insulation that has been sprayed onto bar joists and the underside of a fire-rated composite steel-and-concrete floor deck. A thicker layer of insulation yields more heat resistance. For higher fire ratings, additional layers can be added. For technical information on the use and application of these products, and UL Directory listings, visit, the manufacturer of Isolatek and Blaze-Shield products

Photo 2

Photo 2 shows insulation that has been sprayed onto steel columns. The columns are partly exposed either because the surface of the steel (primer paint) was not clean enough, or because the batch was not evenly mixed (wet or dry spots in the spray mixer). These areas, and others like them, will have to be cleaned and resprayed before the building inspector’s next visit.

Any brands or brand names noted above are used only as examples, and the Web sites only as sources of additional information. Reference to them is not an endorsement of either product or manufacturer.

Gregory Havel is a member of the Town of Burlington (WI) Fire Department; retired deputy chief and training officer; and a 30-year veteran of the fire service. He is a Wisconsin-certified fire instructor II and fire officer II, an adjunct instructor in fire service programs at Gateway Technical College, and safety director for Scherrer Construction Co., Inc. Havel has a bachelor’s degree from St. Norbert College and has more than 30 years of experience in facilities management and building construction.

Article and photos by Gregory Havel