Casting fins off of a repro?

[Cecil]

I had a customer bring in two identical repro crappies with broken fins. One has a broken tail fin and the other does not and vice versa with the anal fin. So if I can make a mold of the good fin I would be able to use the cast fin on the one with the broken fin etc.

What would be the best material to use to mold these fins? I would like to use Bondo, so would a vaseline release work or Syn Lube? Or can I make a two piece alginate mold?

I already have the material to cast the fins out of.

[AnglingArtisan]

Imbed the fin in high fiber. Make a few "keys" around the edge.
Brush on a coat of PVA(poly vinyl alcohol)...let dry
Repeat.
Mix up a cup(small container) of Bondo with a few shots of polyester resin
Catalyze with the red Bondo hardner.
Pour this mix over the fin and around it(covering all the "keys".
Let cure.
Mix up a small batch of fiberglass resin.
Place fiberglass mat over the mold and wet it out with the resin.
Let cure.
Flip over the mold.
Wax the flange and fin with a soft wax(turtle wax works)
Then coat with PVA and repeat above steps.

[Cecil]

Much appreciated! I guess the part that was questionable to me was what to use as a release.

[Frank E. Kotula]

Morning Cecil. Here's what to do real quick. I know you follow breakthrough magazine. Follow the same steps in there on casting fins from Gary.
I do this often so I will suggest the you put a light coat of wax on your fins that your going to make a mold out of. After that make sure you clean the mold real good and use Vaseline and minerial spirits for your mold release. One third third Vaseline and two thirds minerial spirits

If you have time then order some fin magic from epo-grip and use this for the fins. 

If not then you can use plain fiberglass resin. I use my own chop made from matt fiberglass. You can get this from the auto store. I cut it into 3/8" pieces and mix it with the resin that already has the hardener in it. Place it on both halves and make sure you have worked out the air bubbles. After that you can clamp them togethere

[Bruce Foster]

Cecil.....good advice on the reply threads......however, in this case, IMO, this is what I would do.....melt some Flex Wax from Dick Blicks......very low temp. wax......just dip the fin in the melted wax untill you have built up a few layers......let cool.......no seperater needed at all, and it will be a one piece mold........remove from fin.....you may have to make a relief cut in the wax depending on the fin shape......re-dip in wax to seal the relief cut......as Frank said, now fill the mold with Fin Magic.......no release needed.....because the Flex Wax can bend, after your initial pour of Fin Magic, as it begins to set, you can shape any desired curve into the cast part.....Flex Wax is semi-transparent, allowing you to see the cast fin as it dries.......once dried, just pull the wax off......you should have a repo fin that requires no grinding or trimming other than the body/fin junction......the Flex Wax is reusable, and this can all be done with little expense and in a very short period of time....You could also use Clear Casting resin or regular fiberglass resin instead of Fin Magic......just another option to your post.....hope this helps

[Cecil]

Thanks guys! And I do have epogrip's product so I'm fine there!