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Thread: how to make the molds????

  1. #1

    how to make the molds????

    Hello everybody,
    suposse that we 've made the styrofoam model in scale 1:1 ,then how we make the molds of it?
    If we put gel-coat on the styrofoam we'll dammage it...right? So, how we can make the molds?
    And besides that, is there any other way to make the molds without using the fiberglass layer building process?
    Is there any other material that we could use it in order to make molds?

    thank you very much,
    waiting your replay

  2. #2
    Senior Member ArashB's Avatar
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    Any opinions on spraying plasti dip over the foam guys? It would be a rubber coating as the end result... but could it negatively react with fiberglass?
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  3. #3
    Senior Member murcie-me's Avatar
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    The solvents in the coating would attack the styrene as it cured. If you want to seal Styrofoam to pull a mold from, just use latex paint and when its cured use either wax or part-all #10 (spray) as a mold release so the gelcoat and resin wont stick to the latex. KILZ sealer is the best for this, apply with a brush or roller.
    Last edited by murcie-me; 03-29-2017 at 10:58 PM.
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  4. #4
    Senior Member ncrazyballa's Avatar
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    Quote Originally Posted by murcie-me View Post
    The solvents in the coating would attack the styrene as it cured. If you want to seal Styrofoam to pull a mold from, just use latex paint and when its cured use either wax or part-all #10 (spray) as a mold release so the gelcoat and resin wont stick to the latex. KILZ sealer is the best for this, apply with a brush or roller.
    good info.

  5. #5
    Quote Originally Posted by murcie-me View Post
    The solvents in the coating would attack the styrene as it cured. If you want to seal Styrofoam to pull a mold from, just use latex paint and when its cured use either wax or part-all #10 (spray) as a mold release so the gelcoat and resin wont stick to the latex. KILZ sealer is the best for this, apply with a brush or roller.
    Aplication with a brush or roller the latex paint?

  6. #6
    Senior Member IKAROS's Avatar
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    Thanks murcie-me.Nice info indeed...
    George, i think thats correct(brush or roller the latex paint)

    Can anyone confirm that the best & the cheapest way to glue styrofoam together is...



  7. #7
    Is foam strong enough to pull a mold directly from? I havent done it yet, but I had read that the foam should to be coated with a hard shell like an epoxy so it doesn't deform when the fiberglass is curing. Is that overkill?

  8. #8
    Senior Member MacGyver's Avatar
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    Guys,

    I'll give you all my two sense. Using cheep Styrofoam from building supply places has a lot of advantages. It's cheep. (We all like cheep). It's easy to find. Shaping, cutting, sanding is also fairly easy. The disadvantages is that it is hard to seal and smooth it well enough to be used for a mold. The best type of foam for this purpose is Urethane based. It will cost you a lot more money but in the long run it will save you a ton of time. With Urethane foams, you can Bondo over it. Apply 2k primers, Urethane primers or what ever you want. It also makes an excellent plug for a mold. You can also purchase it is different density's depending on your project. Two part Urethane pour foam is generally available in 2lb, 4lb, and 8lb density. The 8lb is so hard you think it was a piece of wood. You can also find the Urethane foam in sheets. Cost varies depending how thick you want it. Since solvents don't have an effect on it, you can also bond them together with just about any solvent based glue, sealer or 2 part primer. Another issue when using multiple sheets of glued together Styrofoam is you will never get it nice and smooth. What ever glue you find to join it together with will be a different hardness than the foam. Which in turn, will never give you a nice smooth part.

    If you decided to make your part out of Styrofoam anyway and need to use it as a plug. Coat it with a water based exterior house paint or sealer. Don't use solvent based. It will just melt the foam and make a mess. Once totally dry, smooth it as best you can without exposing the Styrofoam and then coat it with a Urethane based primer like Slicksand or whatever. Once it's very smooth, put on multiple coats of mold release wax and a coat of PVA. In most cases, if your plug is nice and slick and smooth, well waxed with no undercuts, your mold should release easily and not damage the foam. What can be an issue using Styrofoam vs Urethane foam is that the paint or primer you used to seal the Styrofoam with does not adhere to the Styrofoam very well. it may bubble, or lift in a short amount of time. You won't have this issue using Urethane foam.

    I have seen a while back that some people will coat or spray a clear epoxy over their Styrofoam part to seal it. That may also be an option to seal the foam but I never tried it. That may lift just like the house paint. I don't know one way or another.


    Hope this helps a little for you all.

  9. #9
    Senior Member MacGyver's Avatar
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    Another comment on your question about molds.

    Yes, their are a lot of different materials that could be used to make molds vs fiberglass. If you are planning to mold a car body or any fairly large part. Your best cost effective option is Gelcoat with Polyester Resin and fiberglass. It's been done for many years with good results. Anything else would be reinventing the wheel.

    You could save money by using outdated resin for the build up after your initial base layer of 2oz of mat, as well as plain gelcoat vs tooling gelcoat. But your molds would not be a durable if you plan on making multiple copy's of your parts.

    What is referred to as a "splash mold" are generally thinner in thickness than a standard mold and may not hold the proper shape when making your part. This can save on cost as well because you are not using as much material. although you may need to spend more time trying to fit your panels together if they are not as straight and true as you would like.

    Fiberglass made in China is also less costly that material made here in the US. Although it does come with a price. The resin doesn't soak into the fiberglass as easily and is a little harder to work with in general.

    OK - I'm done typing for a while.... good luck buddy!

  10. #10
    Senior Member ncrazyballa's Avatar
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    I use this gun to spray house paint (latex primer). just thin the paint down 5-10 percent. put enough layers on and you can wet sand it and have a good surface. Although before even putting on latex i usually spread a layer of spackling and sand it. There is this stuff called pva dry wall sealer its almost like liquid spackling, i used it once as buildup over the plug, sprayed it with a textured spray gun, but it seems to crack in some spots. it sands like a harder version of spackling and produces a great surface finish. im thinking i can mix it with latex primer to keep it from cracking.
    Last edited by ncrazyballa; 04-01-2017 at 08:57 AM.

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