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Casting Foam Problem

Discussion in 'Habitat and Exhibit' started by pir^2h, May 14, 2019.

  1. pir^2h

    pir^2h Retrievers give you the bird

    I will try to provide every detail I can to maybe someone can tell me what is going wrong here.

    1) I attempted to copy a rock that I liked the shape of. I put two thin coats of latex on it then another thicker layer with tire shavings to give it a little more strength.

    2) I built a wood box, put in foam in the bottom, turned the rock upside down (latex down into the foam) then filled the sides with foam. Let it sit overnight and removed the rock from the latex skin.

    3) Mixed up a couple batches of part A and part B, added some powdered tempra paint black to the foam and stirred it up and poured it. It all looked like it was going to work. I left it alone overnight. Today I went out to look at it thinking I was going to remove this artificial rock. But, on one end it was like the foam had imploded. There was a section where the foam had caved in and it had a hollow spot under part of what didn't collapse.

    Several things are going through my mind. Was the foam old? I bought it about three years ago. The "A" part had globs that had solidified but I only used the liquid part. (The "B" was still very liquid, not hardening at all)

    Was it the tempra paint? Well that didn't make sense either since I had done a small sample pour with the same tempra and all worked well.

    Was it because I used a latex mold? Never used this before. Possibly?

    Right now I am not sure where to go. I can't be the only one this has ever happed to so I am hoping someone can share with me what they did to fix their problem.


  2. Lance.G

    Lance.G Well-Known Member

    If that paint is water based it will react with the urethane foam. The larger amount of paint the more it reacts. Also sounds like your foam is pretty old. I like the paints invative polymers makes for mixing with urathane. Smooth on makes some also. Hope this helps.
    George likes this.

  3. Keith

    Keith Well-Known Member

    Foam absolutely has a shelf life. Part A will take on moisture over time and get chunky like you describe, especially if left exposed like in a cup over a few days. This seems to occur more in the summer when we have high humidity in Minnesota.

    Whats really frustrating is altered forms, only to have the foam collapse after the skin is on and sewn up.
    pir^2h likes this.
  4. Always add dry powder tempra.