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Foam shrank?

Discussion in 'Molding and Casting' started by Nina Lukaszewicz, May 15, 2007.

  1. Nina Lukaszewicz

    Nina Lukaszewicz Outdoor Dreams Taxidermy

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    I had a foam fox head that I casted (with two part urethane foam) and it was fine for two days, but today it completely shrunk and warped! it was so weird, I'm not sure as to what could have caused it, but ...could it be the sealant spray that I put on top of it that did this?
     
  2. newbirdman

    newbirdman New Member

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    I've had the same thing happen a few times myself . It looks great one day and the next like its a 100 years old and all shriveled up . I think it might have to do with humidity when it was made or you used too much of one part ( not equal amounts ). Rick
     

  3. It sounds like the sealant spray, what kind was it? It could be the ratio that you mixed it. You might have a bad batch in one of the 2 parts. Have you used it before? Is there an expiration date on it? Humidity usually takes awhile to make it shrink.
    Darwin
     
  4. bill@hogheaven

    [email protected] New Member

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    Use fresh foam & lose the sealant. Old foam can do funny stuff, a sealant is totally unnecessary.
     
  5. Nina Lukaszewicz

    Nina Lukaszewicz Outdoor Dreams Taxidermy

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    This was the two part foam I got as a sample from Innovative polymers. The sealant was an acrylic clear coat spray. Oh well, I know not to use it anymore, and now I am just going to clay up the original skull and use that for my head form. more accurate anyways.
     
  6. bill@hogheaven

    [email protected] New Member

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    Hey Nina...did the body parts do the same thing? Did you seal them?
     
  7. Nina,
    How long did you leave the foam in the mold? Removing the foam from the mold too early will cause it to crack or shrivel. Was it an open mold or closed? The solvents in the acrylic can also cause your foam to collapse. Inproper mixing can also cause your foam to collapse. Did you use a drill mixer or did you try mixing by hand?
    You can always give me a call Nina and I will answer your question rather than posting it in a forum. I'm more than happy to help you out here. Some urethanes are very tricky to work with. Its kind of like a clear urethane, if its not processed just right, it can look like a block of swiss cheese rather than a nice clear cast system. Urethanes can be funny animals, thats why we're here to help as much as we can.
     
  8. Laurier

    Laurier Active Member

    it sound like improper measuring, and mixing , with humidity in the air. If you do it right it will work perfectly , I got foam from Scott as well (Polymer Guy) and it is very good foam , nice skin ti it.
     
  9. Nina Lukaszewicz

    Nina Lukaszewicz Outdoor Dreams Taxidermy

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    I mixed it by hand in a small cup since I did not need a big amount. I was only pouring a fox head. I do have a drill mixer that I use for plaster mixing. I kept it in the mold for about a half hour and took it out because I was excited to see how my first casting would turn out. I then trimmed it and dremeled it a day later so it looked more like the original skull. So far the legs I have casted are holding up nicely.
     
  10. Laurier

    Laurier Active Member

    maybe the mold still had moisture
     
  11. George

    George The older I get, the better I was.

    Guys, humidity and moisture have nothing to do with this. Remember, this stuff is WATER BLOWN foam industrially where hot water is used as a carrier.

    Nina, what I suspect is two fold. I use a bent wire on an electric drill to insure that I have complete mixing of the products so tha it looks like tapioca pudding. Still, if I do not use EXACTLY the same amounts, there is sometimes shinkage. Part "A" seems to be the more critical part, so I use a new, clean, gradated cup to measure the parts before mixing. When I'm using plaster, I paint the inside with Vaseline and I use multiple bungee cords to hold the halve together. I usually allow several hours as a minimum for body casting and I make a very SMALL vent hole to allow the excess to blow out. Still, I often find the cast has expanded the mold.
     
  12. hidvalltax

    hidvalltax Dont travel faster than your guardian angel can go

    George I have learned the expansion the hard way to, I think thank Nina just did not let it cure long enough, I have had the same things happen
     
  13. Laurier

    Laurier Active Member

    George humidity in the air will most definitely cause a problem like this. check it out for yourself I did.
    ask polymer guy , he is only a tech.
     
  14. Jim B

    Jim B Active Member

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    That's correct.A very small amount of water will definitely have that affect.Nina,always remember,there can be NO residual moisture in your mixing vessel.It has to be bone dry.I always measure both A+B in seperate cups so that I can be sure the amounts are exactly equal.I see people guess at it but you can see what problems arise from one bad pour.It's not worth taking chances on.Remember also what I mentioned earlier about letting the plaster mold dry completely.Fresh plaster contains a lot of water.If your cup was absolutely dry,my money would say that the 2 parts of foam weren't measured exactly equal.I've used a lot of different products to seal plaster molds and have never had a problem with any.
     
  15. Laurier

    Laurier Active Member

    Jim you hit the nail on the head , but , if I am correct ( NINA ) your mold was very dry. I would say it was humid in her shop that day, rainy day , or high humidity.
    You should have equal part A + B , BUT you can cut back a little on the A , it will not rise as much or as fast , sometimes this is needed , for sceneries.

    If you add 2 or 3 drops of water to your A or B foam before you mixes ( NOT FOR POORING A MANIKIN )
    your foam will rise much more , the water makes it foam more , you still get a skin on the foam ( this works well on sceneries only )

    This is the reason I would think was done at high humidity in the air , only Nina would know for sure.
     
  16. Nancy C

    Nancy C Well-Known Member

    I have had that happen to me occasionally.
    I think it occurs when I don't get the parts measured exactly right or mixed well enough. (I am very careful to avoid moisture contamination.) It will foam up almost TOO fast, but then it collapses within a few days. I suspect mixing problems when only one part of the form collapses.
    I have learned not to trust the forms that expand too fast or the ones that are still making crackling noises when I unmold them. If I'm not sure, I set the suspect ones aside and make fresh ones. If the strange ones are still unchanged after a week or so then I will put them in the "okay to use" box.