Adhesive Failure on Oily Galvanized Deck
On a warehouse project, SFRM is being applied to galvanized metal deck and steel joists. The specified material is a cementitious SFRM with a project-specified minimum bond strength of 150 psf when tested by ASTM E736. The deck was fabricated with a visible oily film; the applicator wiped it with solvent but did not apply a primer because the primer was not listed on the approved submittal. Three adhesion tests are performed: two read 180 psf and 165 psf; one reads 95 psf and shows a clean separation from the deck, leaving bare galvanized metal. The relative humidity is 85%, and the deck surface is 48°F. The applicator wants to overcoat the failed area and proceed. The inspector must evaluate the failure, decide corrective action, and determine what retesting is needed.
1. Interpret the 95 psf test result. What does the failure mode indicate?
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The 95 psf result is below the project minimum of 150 psf, so it is a failing test regardless of the two passing results. The failure mode is important: a clean separation from the deck leaving bare galvanized metal is an adhesive failure at the substrate interface, not a cohesive failure within the SFRM. That points to a substrate problem, such as residual oil, inadequate cleaning, or the absence of a required primer or bonding agent. The high relative humidity and 48°F deck temperature may also have affected cure and bond. The inspector should not treat the single failure as a random outlier without investigating the substrate preparation, because the same condition may exist beyond the tested location.
2. What corrective action should be required before overcoating or retesting?
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Overcoating is not acceptable because it would leave the failed bond in place and hide the defect. The contractor should remove the failed material and extend removal to sound, bonded SFRM around the test area. The exposed deck must be cleaned to the manufacturer's requirement, including removal of oil or other contamination, and the approved primer or bonding agent must be applied if the product instructions require it. The contractor should also correct environmental conditions if the manufacturer limits humidity or substrate temperature. After the repair cures, the area should be retested by ASTM E736. The inspector should verify the cleaning method and primer approval in the submittal, because the applicator's earlier decision to omit primer was not supported by an approved project document.
3. What retesting and documentation are needed to close the nonconformance?
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Retesting should cover the repaired area and a sufficient number of adjacent or randomly selected locations to show that the substrate preparation problem has been corrected. Each test should record the location, date, test value, and failure mode. The inspector should also record the surface preparation method, primer product and batch, environmental readings, and the extent of material removed and replaced. The discrepancy report should reference the failed 95 psf result and the corrective action. Closure should require passing ASTM E736 results at or above 150 psf and a visual check for delamination. If retesting fails again, the contractor should remove additional material and repeat the repair rather than adding more SFRM over a known bond failure.