I have used it for a few things, and if you are not carefull, it will do more damage than good. If shot into like a fuse, and not enough expansion room is left, it will blow the fuse wide open. When it dries, it dries with a hard shell, but the center is softer and not easy to sand or shape.

All around, I would advise against it. It won't do you any good, its not needed, and it will not add strength like you are thinking. You can add strength other ways.