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? regarding bondo/resin molds

Discussion in 'Fish Taxidermy' started by Beavis, May 23, 2008.

  1. Beavis

    Beavis Member

    I'm new to this, I've molded a couple fish in the last six months, and am very pleased with the results. (thx Gary) I prefer to cast with gelcoat/fiberglass, but smooth cast seems to bring equally good results. I have been using Syn-Lube as a release agent. I wax and buff the molds with turtle wax, (I don't think its carnuba). I know these type molds deteriorate over time, but my molds seem to start going bad almost immediately. I couldn't get four good casts out of my last, a nine inch hybrid bluegill. I'm still learning, so I do make mistakes, consequently I have to make a few casts to get one perfect. I have two fish I will be molding soon, so I'd like to get this sorted out. Whatever it is I'm doing wrong, it causes the molds to pit, lose detail and become very rough. Should I try a different release agent? Is smooth cast or gelcoat more "abrasive" to the mold? And while I'm on about this, is there a method of molding that does less damage to the fish than the bondo/resin technique? I figured this is the best place to get an answer quickest, if the mod(s) see fit move it to beginners or molding/casting. Thanks
  2. BIGUN

    BIGUN Member

    Beavis- are you using PVA? the stuff is great because the bondo mold and gelcoat fish never actually come in contact with each other. Bondo is not very hard or stable and your asking a rigid mold to produce several rigid parts- alot to ask. Maybe consider making ONE really good part and then remolding it with a dense fiberglass mold or a silicone mold with a rigid shell mold.
    As far as molding methods- just don't le the fish cook too long or the mold get too hot- all the methods, except silicone and geltrate produce exothermic heat.


    GBRUCH "I am nothing without christ".....John 15:5

    I am very glad you are trying your hand at molding fish.
    To help with your question-the Bondo will break down--mine turns powdery sort of. I am not absolutely sure what causes it but I speculate heat generated from the casting is a factor.. Here a bluegill mold produces 4-7 casts. Trout are about the same as the panfish but on bass 3-5 seems normal for me. Be aware that with each pull the mold will break away a bit at the undercuts --thats how it goes with bondo/paster molds. You shouldn't need to make several casts for perfect--the best cast detail wise will always be the first one due to the breakage issues.

    Jeff Mourning and myself will be molding and casting a fish at the NTA----perhaps attending that seminar can get you on track

    I cannot answer about the smoothcast cause I never tried it----perhaps you can give it a whirl and post your results.

    RTV or alginate will do much less damage to the fish.
  4. If you get a good mold and you want many casts then the best plan is to use that first pull as a master cast.
    Chase and repair any imperfectionsin the first cast and them mold that cast with RTV; you will get a lot more pulls out of the RTV.
    Save the original "master" cast, and when the RTV mold is shot, you can mold it again!
  5. Beavis

    Beavis Member

    Thanks all for the quick replies. Gary, if you molds are good for that limited number of casts, I can't be too far off track, and yes, my first cast is always the best, as far as detail is concerned. Let me describe this in greater detail. I swish a thin coat of gelcoat around each half of the mold, using care to not get any on the fins or tail. While this is setting up, I paint a thin layer of straight fiberglass resin into the fin and tail areas of each half. Fill the mold as usual and clamp. When I say perfect, I want the body to be gelcoat white with almost transparent fins, with a perfect "junction" where fin meets body. I don't want to mold the fins separate, simply because I'm afraid of not achieiving that perfect "junction". Using this method, I get very realistic, thin fins albeit rigid and extremely fragile. Its hard, (at least for me) to de-mold it perfect the first time. Do any of you see any aspect of my method that could be improved? I may try to mold with RTV this next time. Thanks again.
  6. I have some fin molds that I made bondo/resin I have pulled somewhere around 40 sets from the molds and they are not breaking down, maybe the resin helps.

    But I also use Johnsons paste wax, its closest to pure wax, turtle wax has acids in it to help clean bugs and road grime from the cars.

    Also I never measure th bondo resin ox or amount of harnder when making fins and heads. just add 15 to 20 drops of mekp per ounce depending on the weather.

    GBRUCH "I am nothing without christ".....John 15:5

    I am wondering still why you need to cast several to get one good one. Where are the problem area(s) one thing I see as a potential problem your not thickening your body cavity unless fill as usual refers to that? This can lead to the body cavity sagging(colapsing) inward due to the lack of strength and support. You also are not strengthening your fins and I assume you have some breakage in the resin fins especially as they become more brittle over time. I demold the cast after soaking the mold in hot water - this softens the bondo and allows easier removal.

    feel free to call 717-834-6501 if you would like