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Discussion in 'Molding and Casting' started by Cory, Feb 18, 2012.

  1. Cory

    Cory Keep an eye on quality!

    For various reasons, lets say I wanted to make plaster a little more rigid in the mold. I.E. using chopped fiberglass in bondo to add rigidity. Would using strips of burlap mixed in with a thick coat over the detail coat get the results I might be looking for?
  2. I've mixed it with long strand fiber glass with good results.

  3. bill@hogheaven

    bill@hogheaven New Member

    Burlap works fine.
  4. hodx

    hodx Herman Darr

    bulap,woodwool,hemp, metal lathe
  5. Cory

    Cory Keep an eye on quality!

    Thanks. Thought it would, just like hearing it from some of the ones who have been doing this way longer than me. ;D
  6. I have used burlap, cheesecloth and fiberglass.
    Both work.
    If you use Burlap or cheesecloth its best to soak it in water before. This allows the fibers to separate a bit and lets the plaster soak in deeper.
    Fiberglass chop works very well. Another trick is adding a hardener to the plaster. There is an additive to concrete you can buy, we used to use casein glue (white glue) in school when we needed many strong molds. We added it in small amounts to the plaster. This worked as a hardener for the plaster.

    Here are a few additional plaster tips.
    Add plaster to water only, never water to plaster. Try to get the amounts right the first time adding more plaster to a mix to thicken it will weaken the plaster buy upsetting the chemical reaction taking place.

    Plaster will set faster as it gets warmer. It is possible to mix a few batches of plaster at once. Then mixing them more vigorously at the time of application will speed the process. The action of agitating the plaster at a molecular level causes friction that creates heat causing activation and faster setting.
    The reason we used this trick was when we needed to do direct sculpture work or plaster lamination for a large mold.
    The initial coat was allowed to set then sprayed with warm water lightly. We then mixed a few small batches of plaster and let them sit. we grabbed one batch and began stirring and applied it to the wettened set plaster. this coat contained fibers and a layer of cloth. as that was being applied we had another person begin stirring another batch..... we continued this until the mold was completed.

    The reason we did it this way was adding plaster to dry set plaster can cause a weaker bond. If you wet the plaster to the point of saturation you can add more plaster and get a full bond.
    Its often better to make plaster molds in one shot to avoid delamination.

    Another thing we did was add small strips of wood to the plaster to add more strength on larger molds.
    The strips were attached with soaked burlap as part of the last coat.

    Plaster is cool stuff and has been used for thousands of years effectively.
    I personally have made large plaster molds of panels that were over 6' high. Its heavy but cheap.
  7. Cory

    Cory Keep an eye on quality!

    THANKS JKnuth. It is amazing what you can learn when only asking a simple question. Thats why this site is the best! I am going to try and implement what I have learned today and see how things work out. If things go good I will try and past pics, if things don't work so good, I'll try again until I get my desired results. For thought: I wish sometimes if I knew I was going to be doing this for the rest of my life, I would've majored in art in college instead of music!
  8. Cool Music hey, what instrument? I ended up spending more time with the Music students rather then the art.
    As far as the Art Major, it would have really depended on your school anyway. I was very very lucky. My school had an amazing foundry and very good professors who still taught the basics.
    Many Programs now focus only on fabrication, found object and "installation" rather then (sculpt, mold, cast)
  9. boarhunter67

    boarhunter67 Active Member

    Get some Fix-All from Home Depot or some similar place. It is similar to plaster, but sets much harder.
  10. Cory

    Cory Keep an eye on quality!

    Well Josh. Lead trumpet. My favorite was of course, big band Jazz! Nothing like a weekend at the bar playing the night away ;D Whats funny is I hung out with several art students, just seemed to get along okay. Thanks for all you do on here Josh. Talk at ya later.