A B737-300 CAPT RPTED THAT THE WRONG DEICING FLUID WAS APPLIED AT SLC AND WAS NOT DETECTED UNTIL AFTER OPS CALLED.

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ON TAXI OUT FROM SPOT IN SLC; N ON TXWY H TO RWY 16L; I HEARD OPS CALLING US ON VHF #2. THEY ADVISED US THAT THE ACFT HAD BEEN DEICED WITH TYPE IV FLUID AND; THEREFORE; NEEDED TO BE DEICED WITH TYPE I BEFORE TKOF. SO; SINCE WE WERE ABEAM THE DEICING AREA; WE MADE A 180 DEG TURN AND TAXIED OVER TO IT. WE DID NOT INCUR ANY ADDITIONAL DELAYS DUE TO THIS OVERSIGHT AND ENDED UP DEPARTING A TOTAL OF 20-25 MINS LATE. IT HAD NEVER ENTERED MY MIND THAT WE'D BEEN DEICED WITH TYPE IV; SINCE THE WX WAS VERY CLR AND NO PRECIP DURING THE NIGHT. I HAD ASKED THE FO ON HIS RETURN FROM HIS WALKAROUND; IF WE NEEDED TO BE DEICED; AND HE SAID THAT THE ACFT HAD ACTUALLY BEEN DEICED AND FLUID WAS STILL DRIPPING OFF THE ACFT; WHICH IN MY SIMPLE MIND TRANSLATED TO A RECENT TYPE I OR MAYBE TYPE II APPLICATION. CONTRIBUTING FACTORS: CLR DAY WITH NO PRECIP. THE PRIOR EVENING; FIRST REAL COLD WX OPS FOR ME THIS SEASON AND NO NOTIFICATION OF THE TYPE IV FLUID HAVING BEEN APPLIED UNTIL WE HAD TAXIED OUT. POSSIBLE REMEDIES: DISCUSSED THIS WITH FO; WHO IS RATHER NEW TO COMPANY AND AIRLINE OPS (7 MONTHS). HE SAID HE DIDN'T KNOW/REMEMBER THE RAMIFICATIONS OF USING TYPE IV FLUID; ALTHOUGH HE NOTICED THAT THE DEICING FLUID WAS GREEN. I THINK I WOULD HAVE BEEN CLUED IN TO START THINKING ABOUT A SECONDARY DEICE; IF I HAD HEARD THE WORD 'GREEN' IN THE FO'S REPLY REGARDING NEEDING DEICING. NORMALLY; I DO REVIEW THE COLD WX PROCS PRIOR TO THE FIRST FLT IN THESE CONDITIONS AND ALSO DISCUSS THIS WITH THE FO. ALSO; I WOULD SUGGEST SOME SORT OF NOTIFICATION TO THE CREW; PREFERABLY WRITTEN (MAYBE ON THE 'ICE-MAN' SHEET WE WERE PROVIDED ALONG WITH THE RELEASE) ANY TIME TYPE IV FLUID HAS BEEN USED.