Cold-Weather Start-Up on Unheated Steel
On a December morning in an unheated Denver parking garage, the contractor is ready to spray SFRM on W24x68 steel beams. The approved design requires 1-1/8 in. of a gypsum-based material over an approved primer. The manufacturer's printed instructions require an ambient temperature of at least 40°F, a steel substrate temperature of at least 40°F, and material storage above 35°F. At 7:00 a.m., the inspector records 38°F ambient, 36°F on the beam flange, and 34°F in the material trailer. Frost is visible on the top flanges, and the contractor proposes to start at 7:30 a.m. because the forecast high is 48°F. The contractor has portable heaters and tarps on site but has not used them. The inspector must decide whether to permit application, what conditions must be verified, and how to document the decision.
1. May the inspector permit application to start at 7:30 a.m.? State the controlling requirements and the decision.
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No. The controlling requirement is the manufacturer's printed application instruction, which the approved fire-resistance design incorporates. At 7:00 a.m. the ambient temperature is 38°F, the steel is 36°F, and the material is 34°F. All three are below the stated minimums, and frost is present on the flanges. A forecast high of 48°F does not satisfy the current condition at the time of application. Starting now creates a real risk of poor bond, freezing before cure, and a material that later disbonds or has reduced density. The inspector should deny the start, direct the contractor to heat the enclosure and the material, remove frost and any condensation, and then verify with calibrated readings that ambient and substrate temperatures are at or above 40°F and material storage is above 35°F. The denial and the reason should be recorded in the daily report.
2. If the contractor heats the garage, what readings and records should the inspector require before spraying and during cure?
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Before spraying, require ambient readings at the application location and substrate readings at several representative beam locations, including flange and web surfaces, using a calibrated contact thermometer. Verify the material temperature and that the stored material has not been frozen. Confirm the primer is approved, dry, and free of frost or condensation. Record the time, location, instrument identification, and each reading. During application and cure, require the contractor to maintain the manufacturer's minimum temperature and to record periodic readings. The inspector should also record heater type and location, ventilation, and any change in conditions. These records matter because the special inspection is not only a visual check; it must show that the environmental envelope required by the approved product was maintained at the time the material was placed and while it cured.
3. Suppose the inspector later learns that spraying actually began at 7:45 a.m. without heat. What inspection action and reporting are appropriate?
Read the worked answer
Treat the work as a nonconformance. Stop further spraying in the affected area, notify the contractor and owner in writing, and document the actual start time, the recorded temperatures, the frost condition, and the areas sprayed. Warm weather later in the day does not retroactively cure a cold-weather application. The inspector should require an evaluation of the in-place material, including visual examination and adhesion/cohesion testing by ASTM E736 at locations representative of the suspect work. If bond, cohesion, or density is questionable, the affected material should be removed and reapplied under compliant conditions. The inspector should issue a discrepancy report, require a written corrective action, and record the resolution in the final inspection report rather than accepting the work on the basis of later temperature rise.