Substrate preparation, surface conditions, and environmental requirements
Acceptable substrate
SFRM bonds mechanically and chemically to the substrate, so the surface must be clean, dry, and sound. Steel must be free of oil, grease, dirt, loose mill scale, loose rust, weld spatter, and form-release agents. Shop primer or paint is acceptable only if the manufacturer and the approved design allow it; galvanized and stainless surfaces often need a manufacturer-approved bonding agent or primer. Concrete and masonry must be cured, free of laitance and release agents, and within the manufacturer's moisture limits.
Environmental limits
Most SFRM products require ambient and substrate temperatures of at least 40°F (4°C) before, during, and after application, with the temperature maintained long enough for the material to set. Manufacturer data may set a higher minimum or a maximum. Surfaces must be above the dew point and free of condensation, frost, or ice. Enclosed spaces need ventilation to remove moisture and dust, and freshly applied material must be protected from freezing, rain, and traffic until dry.
Worked example
At 7 a.m. the air is 42°F but an infrared reading of a column flange is 36°F. The product data sheet says 'substrate minimum 40°F, maintained 24 hours before application.' The air reading does not qualify the steel. Correct action: stop, heat the space, recheck both air and steel, and document the 24-hour hold before spraying.
Traps
Recording only air temperature; checking temperature once at start-up; spraying over a compatible-looking primer without written approval; ignoring condensation on cold morning steel; failing to mask ducts, windows, and finished surfaces.