Air carrier Captain reported an over-wing inspection prior to takeoff in light freezing rain conditions revealed de-icing fluid was no longer on the wings at a time well short of the calculated holdover time. Reporter stated he considers this a de-ice fluid failure incident and suggests researching holdover times in the interest of safety.

Narrative

This report is to document a Type IV fluid failure that occurred prior to the elapsing of the lower holdover time. The METAR read as follows: ZZZ 04KT 9SM -FZRA SCT050 BKN065 OVC080 M03/M07 A2970 RMK AO2 FZRA SLP060 P0000 60000 I1000 I3000. The Type IV fluid applied was Dow Chemical UCAR FlightGuard AD-49 at 100% concentration. The start time of the Type IV fluid application was XA05L. According to our holdover time table; in the present conditions; the holdover time is between 46 minutes and 1 hour; 5 minutes. Taxi to Runway 10 began at approximately XA15L. The airport operations crew was working through a continuous freezing rain event; applying deicing fluids onto airport surfaces. Runway 10 was unusable for approximately 20-25 minutes; beginning when we approached the hold short line ready for departure. Several Airport Operations vehicles requested and received clearance to conduct a deicing fluid application and runway assessment. At the conclusion of their assessment; 3 arrivals were on final; further delaying our departure. When the last arrival was on short final; the First Officer and I conducted a pre-takeoff check by looking at our wings to determine the condition of the anti-ice fluid. While my winglet area looked good; the surface I could see from the base of the winglet to approximately the midpoint of the wing was now clear; with no evidence of Type IV green dye anywhere. I sent the First Officer into the cabin to get a better assessment. He easily concluded that our Type IV fluid had failed and showed me a few pictures he had taken. I agreed; and we went back to the gate. This determination was made approximately 30-35 minutes following the Type IV application start time. After some coordination with our flight attendants and ATC; we began our taxi back to the gate at around XA45L and blocked back into the gate shortly thereafter. We refueled and deiced a second time.The cause of this event was a Type IV fluid failure due to freezing rain.The holdover time for Dow Chemical UCAR FlightGuard AD-49 may need to be lowered in consideration of actual conditions experienced during a light freezing rain event with an ambient temperature of -3 Celsius. We noted that the holdover time for the same at -2 Celsius was considerably lower; with a holdover time range of 15-19 minutes. This is a drastic difference over the 46-65 minutes of holdover permitted for the same at -3 Celsius.