I DON'T KNOW IF THIS WILL HELP, I'M NOT A BATHTUB REPAIR EXPERT BUT I HAVE REPAIRED TUBS LIKE THIS BEFORE. I HAVE USED BOTH EPOXY AND FIBERGLASS REPAIR KITS FOR CARS AND BOATS. IF ITS IN THE BOTTOM YOU MAY HAVE TO USE SCREEN AND FIBERGLASS AND MAKE A BIG PATCH AND FEATHER THE EDGES OUT TO MATCH,THEN PAINT WITH EPOXY PAINT OR OTHER TOUGH PAINT. MAKE SURE YOU USE A MASK IF SANDING AND PAINTING I HOPE THIS HELPS