So, I'm very, very new to all of this. Pardon the mess in the picture.

I'm  trying to figure out the best (or even good) way to add flanges to this fender in order to get a smooth surface on the mold. The shape is pretty complex (for me, at least). I've tried layers of masking tape, HVAC aluminum tape, corrugated plastic sign board - very difficult to fit to this shape, especially in the section in the bottom-left part of this picture - and some other stuff I can't remember.

Aluminum tape is the easiest to work with as it molds nicely and sticks to the part without jumping through hoops. However, it has a very anti-smooth surface. The resulting mold is something that I feel won't seal well for bagging.

Any suggestions?  Somebody  elsewhere mentioned using foam blocks, but I'm not sure how to implement that.




Also, since I can't find the "edit" button: I'm happy to trim the part when it comes out of the mold. The "top" of the fender, in the bottom-left of the picture, has a shape like

```\___/```\___/```

(pardon ASCII art). Cutting out the fjords after demolding is perfectly acceptable.


I'm sure I'm over-thinking this.

Corrugated plastic sign board is great for this, I think you should give it another go. It is very flexible perpendicular to the corrugations, so when cutting it just make sure you cut your flanges in the flexible direction of the board. For even more flexibility you can score the back of the sign board without cutting through the surface. 

I'm yet to find an object I can't flange with coreflute.