A DC8-63 CARGO PIC PERFORMS AN OVERWT LNDG DURING INCLEMENT WX AFTER BREAKING OUT OF A 300 FT OVCST AT CYQX; NF.

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APCHING GANDER INTL ARPT; THE ATIS INFO RPTED WINDS 165 DEGS AT 10 KTS; VISIBILITY 2 1/2 MI; RAIN; BROKEN CLOUDS AT 300 FT; OVCST 1200 FT; ALTIMETER 29.62; RWY 4 IN USE. A VECTOR OF 170 DEGS WAS GIVEN TO APCH RWY 22 AND THEN WE WERE ADVISED OF THE APCH LIGHTS OTS AND A NEW VECTOR TO INTERCEPT THE LOC RWY 4. I CALCULATED THE TAILWIND OF 10 KTS AND THE RWY COMPONENT WHICH WAS 2 KTS. THE LNDG WT WAS 249000 LBS. THE MAX LNDG WT FOR THAT RWY (WET) WAS 255400 LBS. THE PENALTY FOR TAILWIND WAS 3200 LBS PER TAILWIND KT; PUTTING ME AT A MAX LNDG WT WITH FLAPS 35 DEGS. THE USE OF FLAPS 50 DEGS IS LABELED ON THE AIRPLANE FOR 'EMER USE ONLY' AND I DID NOT CONSIDER THAT AS AN EMER -- ONLY A MAX LNDG WT. WHEN I HAD THE RWY IN SIGHT; IT WAS ALMOST AT THE MINIMUMS. WE CALLED THE RWY IN SIGHT; GOT THE LNDG CLRNC; AND A NEW WIND OF 190 DEGS AT 10 KTS. AT THAT MOMENT; I REALIZED THE HVY RAIN AND MORE TAILWIND WHEN I WAS COMMITTED TO LAND. AT TOUCHDOWN; WE SELECTED THE FLAPS TO THE FULL DOWN POS (50 DEGS). WHEN I PRESSED THE BRAKES; I FELT NO ACTION NOR REACTION. THERE WAS A LOT OF SLUSH ON THE RWY. QUICKLY; I NOTICED THAT THE ACFT WAS IN A HYDROPLANING SIT. THE ACFT STARTED TO SLOW DOWN AT A VERY SLOW RATE AND I HAD VERY LITTLE CTL. GANDER INTL HAD A NOTAM OF THE LAST 1020 FT OF RWY 4 CLOSED. ALL THE LNDG NUMBERS WERE PREDICATED WITH THAT RESTR. AT THE RESTR END THERE WAS SOME BARRICADES AND WITH THE THRUST AIR COMING OUT OF THE REVERSER; WE BLEW 4 OF THE BARRICADES. THE ACFT WAS NEVER IN CONTACT WITH THE BARRICADES OR ANYTHING ELSE. THE ACFT SUFFERED NO DAMAGES AT ALL NOR DID THE BARRICADES. AFTER MAINT INSPECTION TO THE ACFT; WE STARTED THE ENGS AND TAXIED BACK TO THE RAMP. FLT CONTINUED TO SPAIN AS PLANNED. THE ATC CTLR AND THE TWR CTLR FAILED TO ADVISE ME OF THE HVY RAIN; THE CHANGE OF WIND; AND THE SLUSH ON RWY 4.