can you use silicone caulk as a mold?

Discussion in 'Replica Props' started by hydin, Mar 27, 2006.

  1. hydin

    hydin Sr Member RPF PREMIUM MEMBER

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    i was thinking about this earlier today, and just now realized i have no clue, and this is probably the best place to ask.

    i have some silicone caulk, never really opened, for a prop bomb i was going to build out of plexiglass.

    i have a small mold i want to make, one piece, and i vaguely recall something about using this stuff in a book i read about mold making.

    so.... any tips/tricks/ideas/etc for this?

    by small mold i mean maybe something around 3" long, by about 1" wide by about 1/2" thick. i just need a one shot casting out of it.

    again, any tips or instructions would be greatly appreciated about this. i dont recall this ever being mentioned in a thread anywhere, but i do remember it in a molding/casting book (same guy who did the mask making book). just not sure what kinda silicone stuff i gotta have, and if i gotta put some kinda release agent on the thing im molding, or what.

    thanks
    chris
     
  2. exoray

    exoray Master Member

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    MOLD RELEASE.
     
  3. jedi5150

    jedi5150 Well-Known Member

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    Having not tried it, I'd say it'd work.. but it seems that this stuff takes a LONG time to cure... and sticks to EVERYTHING, so yeah, mold release would be IMPORTANT.

    Just my $.02 worth....

    Doug
     
  4. Boba Frett

    Boba Frett Sr Member

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    100% Silicone rubber (clear is the best) can be used. I do it all the time for things I want just a few casts of.

    Take a bowl of hot soapy water (dishwashing liquid) , empty the whole tube of silicone into the water and use. Keep your hands wet and it won't stick to you.

    Make sure you spray acrylic clearcoat on what your casting.

    Bigger stuff make a plaster case mold :)

    I just made one today for a one cast I need myself.

    Dries in a few hours depending on thickness.
     
  5. Umori Bawar

    Umori Bawar New Member

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    as boba fett siad 100% Silicone rubber,

    but what i do is just empty what im gonna use of the tube into a plastic bowl then add a few drops of glycerin (first time i heard about doing this plunty years ago i had a hard time finding a nice liquid clycerin at a place like walmart till one of my buddies told me just to use some babylax (liquid clycerin supositories for babys))), and a few drops of craft water based paint and mix togeather (paint just makes it easyer to mkae sure its mixed well, it will create a silicone past like that will dry usaly in half hour to hour,

    i do often to create fast molds for items im casting just to retool in a way. but i have done it once to create a mask mold, firend asked me to make him the sithlord mask form kotor 2 so he could wear it with his costume to ep3, which wouldent ahve been a challage if he dident ask me 6 hours before its relases, lol.

    but yea it will work.
     
  6. Boba Frett

    Boba Frett Sr Member

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    Hmm , I will have to try it that way :)
     
  7. hydin

    hydin Sr Member RPF PREMIUM MEMBER

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    i bought some "mini loaf" pans at the store today, and used my caulk to make the mold.

    (boy that sorta sounds dirty somehow..)

    its curing now. man this stuff is stinky. im going to either bring it with me to work and let it bake in the sun, or maybe leave it outside on the back porch and let the heat help with the curing of it.

    did i mention this stuff stinks? igh.

    hopefully, in a few days i will have a pretty nifty prop thread to show off though :)

    thanks for all the tips guys. im gonna pick up some glycerin and paint to try that idea as well. this stuff is a LOT less expensive than silicone, and for cheap and dirty molds (if it works ) its worth its weight in gold.

    chris
     
  8. Hand-Schaub

    Hand-Schaub Well-Known Member RPF PREMIUM MEMBER

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    this entire piece (40 feet long) was molded using 100%silicone form the tube. I was an assistant on the projec and YES.... my arms hurt after molding it.
    [image]http://www.artcap.org/h.jpg[/image]
     
  9. TFrosst

    TFrosst Sr Member RPF PREMIUM MEMBER

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    So do you still need to put mold release on the item being molded? what exactly does the glycerin do?
     
  10. Goldenrod

    Goldenrod Sr Member

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    I'm not sure,but i have seen the hot melt glue used as actual costume pieces pulled from a fiberglass molds.Guyver suit. It looked great.
    Let us know how the caulk idea comes out?
     
  11. Goldenrod

    Goldenrod Sr Member

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    what about a silicone spray for mold release?
     
  12. hydin

    hydin Sr Member RPF PREMIUM MEMBER

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    is there any way to "kick" this stuff a bit to get it to set faster?

    mine is still in the "goo" stage with a thin skin on top from last night.

    i have it out in the sunlight now, but im thinking maybe a small toaster oven or something in that realm to speed the curing up a bit, but i dont know what kind of temp to look for, and if this stuff is flammable or what.

    any tips/tricks are appreciated.
    chris
     
  13. Jedirick

    Jedirick Sr Member RPF PREMIUM MEMBER

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    Try a warm oven 200 degrees for a few hours.
     
  14. darthchiro

    darthchiro Well-Known Member

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    Did you use the glycerine in the mix? That will kick it and make it set, I can usually unmold within 1/2hr -45 minutes. Its not 100% cured you will still smell the "vinegar" but it is stable. If you don't use the glycerine/waterpaint, you have to use thin layers and let them set before the next one. It will still set but you will have to leave it alone for several days. whens its fully cured the rubber doesn't stink at all, smells kind of like new shoes .
     
  15. hydin

    hydin Sr Member RPF PREMIUM MEMBER

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    nah, im gonna do the glycerin in the next batch o molds. this one was just glopped out of the tube and onto the originals.

    ill give the oven a shot. hell, cant stink the house up any worse than castincraft does :lol

    thanks
    chris
     
  16. Boba Frett

    Boba Frett Sr Member

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    It should have set within a few hours at the most.
    Did the tubes say 100% silicone or 100% silicone rubber?

    I have only used the rubber type.
     
  17. hydin

    hydin Sr Member RPF PREMIUM MEMBER

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    100% silicone rubber sealant.

    DAP plastics if it helps, the clear kind.

    the mold is about 3 inchs by maybe 2 wide, and about 1/2 to 3/4 inches thick though.

    that might be the problem.

    ill give it a few more hours in the oven.

    chris
     
  18. Durasteel Corporation

    Durasteel Corporation Well-Known Member

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    Do remember a viscosity counts for a lot.....will it run into all the nooks and crannies.....will it flow into the places you need it to go?

    Viscosity is the main reason I dont tend to use tube silicone...I buy mixes. You can control more elements this way too.
     
  19. Jayrcee

    Jayrcee New Member

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    Just to preface what I am about to post...I don't know who posted this silicone mold recipe originally, nor do I remember where I got it from on the internet (I saved it to my computer a few years ago). If anyone knows, please let me know and I will be more than happy to give them credit. The information here has been valuable to me and I hope it helps someone else out.

    "I was just lurking around your site when I came across some references to making molds from silicone sealant (caulk). There are a few things one should know about this process that will make it a whole lot easier.
    First off, use only 100% silicone, preferably clear. DAP makes a pure silicone sealant as does GE. GE markets both Silicone I and Silicone II formulas but either will work. Siliconized latex caulk or any other silicone blends will disappoint you every time. Even the colorants used to get black, white, and almond silicones alter the characteristics of the product. The colored silicones will work, but trust me, start with clear.
    Second, silicone caulk does not cure well in thicknesses beyond 1/4 inch. The skin that forms eventually becomes thick enough to encapsulate the uncured silicone which can remain soft for days or weeks. In very thick layers, the inner silicone may not cure at all. Some people have tried to market "catalysts" for silicone caulk. For tin or platinum cure two-part silicones, you do have to have a separate catalyst, but the catalyst for silicone caulk is water. Pure water does not disperse well in silicone but there are two vehicles that provide the required moisture and can easily be incorporated into the caulk, acrylic paint and glycerine.
    It doesn't take a lot of either to do the job and don't try to use them as a thinner for the silicone. Too much will result in a product that sets up very fast, but is very weak. The glycerine has the added bonus of reducing the adhesion of the silicone, making it easier to remove from the object being copied.
    I use the hobby acrylics that come in small flip-cap bottles. About three drops per ounce of silicone is sufficient. I add the glycerine by dipping a tongue depressor size mixing stick into the glycerine (available at any pharmacy, I've found K-Mart to be the cheapest). Dip the stick into the glycerine about a half inch for each ounce of silicone. For large batches a half teaspoon of acrylic paint and a teaspoon of glycerine will cause a uniform cure in a full caulking tube's worth of silicone.
    The silicone will not seem to take the glycerine right away, but keep mixing and soon it will all come together. The paint makes mixing easy, just stir until the color is uniform. When mixing, be careful not to whip air into the mixture. Bubbles become trapped and result in holes or spongy spots in the surface of the mold.
    This formula should give you about 15 minutes working time with a cure in 1-3 hours depending on heat, humidity, and variables in different brands of products. To be safe, allow 4-6 hours (or better yet, overnight) before demolding important projects).
    This mold making material will come off of most hard, non-porous surfaces without the use of a mold release. Plaster or clay can be sealed with flat acrylic spray available from art supply or craft stores. A tablespoon of Ivory dish soap can be mixed with a pint of water and bushed over non-porous or sealed surfaces and allowed to dry for an extra measure of security. You can also use the soap mixture on organic surfaces such as leaves. Don't use petroleum jelly or cooking spray. They work, but what a pain in the . . . , well, they make spreading the silicone on the model almost impossible. Don't use silicone based release sprays. They work great for every other molding material I know of, but they become part of a silicone mold and lose their effectiveness.
    Carefully paint a detail coat on your model with a disposable brush, making sure to work it into all the details. Silicone can even handle minor undercuts due to its elasticity. Once the surface is well coated, add a layer of silicone 1/2 to 3/4 of an inch thick. You can make a neat surface on the outside of your silicone mold by smoothing it with your fingers wet in the same Ivory and water solution. Allow the silicone to fully cure. Molds of small objects need no additional support. Larger molds should be surrounded by a wall of wood or plastic at least one inch taller than the highest point of the silicone and leaving about an inch of free space all around. Coat the back of the cured silicone, the surface on which it is sitting, and the inside of the retaining wall with petroleum jelly (it's OK at this point) or your soap mixture and pour a plaster mother mold over your silicone mold.
    Once the plaster has cured, remove the retaining wall and invert the entire assembly of model, silicone mold, and mother. Gently remove the model and then carve a small notch at some point where the silicone meets the plaster. This is just a reference point which will allow to realign the silicone mold with the mother.
    Clean the silicone mold with acetone or Ivory and water. Store it in the mother mold, dry and out of sunlight. It should last for years and give you many castings. Any mold release can be used with it, but typically cement and plaster can be cast in it without any additional release.
    To cast in this type of mold, place the mold in its mother prior to filling it. After the cast has cured, lift the cast and silicone mold out of the mother mold together, then gently pop the cast out of the silicone mold.
    I hope this wasn't too lengthy and confusing, but it may help you avoid the trial and error I went through.

    Silicone caulk is not as strong or elastic as two-part mold making silicones, but it is not as expensive either, $3 per pint compared to $18-40. If you must thin it, use xylene, with appropriate gloves and ventilation or respirator. Thin sparingly, as this further reduces the strength of the end product and results in a softer mold that is more likely to deform under the weight of plaster or cement.
    It will handle modest undercuts due to its flexibility. If the undercuts are more severe, the silicone mold can be slit with a razor blade or xacto knife, along one side, in a line that will facilitate the removal of the model and subsequent castings. The slit will be held closed with tape, an elastic band, or by the mother mold, during casting. A fine line will be left on the cast, which can be cleaned up after demolding. Very complex designs can require molds with two, three, or more parts and require more expertise and experience than I can pass on here.
    Several of the silicone manufacturers have good tutorials on their sites. A link to one of them is posted below. Dan Perez Studios also has a tutorial on their site which explains the making of a silicone mold for a complex plastic model.
    The best book I have ever found on mold making is The Prop Builder's Molding and Casting Handbook by Thurston James. It covers silicone as well as a couple of dozen other molding and casting materials aimed at film and theater.

    If the silicone is curing unevenly or too slowly, you can try adding some heat and humidity. Don't place water in direct contact with the mold, but you can try something along the line of placing it in a small bathroom with a hot shower running or place it on a rack above a pan of hot water in a cardboard box. Both the heat and the humidity will help curing. Don't get it above about 100 degrees F.
    If you need a fast plaster shell for it, you can buy a roll or two of plaster gauze from a hobby or craft store. This is pretty much the same product as doctors used to use for making casts for broken bones. Two or three layers should be sufficient to make a quick mother mold over the cured silicone. An alternative would be to mix plaster of paris to a pancake batter consistency with very warm water. Fold a piece of cheese cloth to three layers thick and dip it into the bowl of plaster. Squeeze out the excess plaster and then lay the triple layer of plaster impregnated cheesecloth over the cured silicone just as you would have used the plaster bandage. Keep this warm and dry and it should cure well enough to be used in about an hour.
    If you are making your casting in plaster, remember that mixing with warm water makes plaster of paris set faster as does drying it in a warm place. Don't spot heat drying plaster with something like a blow drier though, as it will promote cracking."
     
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  20. TKBIG

    TKBIG Active Member

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    Dang. When will I learn to ask? :unsure

    I attempted an experimental DAP silicone mold a couple of weeks ago and messed the thing up all to heck. :cry

    Good info here guys... Many thanks.... :)
     
  21. hydin

    hydin Sr Member RPF PREMIUM MEMBER

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    awesome tutorial...

    i wish i'd had it at the start of this project.

    right now, dear sweet zombie jesus, the house smells horrible.

    i put the silicone in the oven (outside), but unfortunatly near the window units vents (was NOT thinking).

    the "mold block" i used to space off the silicone was some cheap * putty play doh kinda stuff.

    it apparently has a baking temp that is very very low. once i demolded it was all i could do not to puke :eek:

    one set of molds came out ok, if not kinda well (not really detail oriented with this stuff, but the rough stuff is there). the other (with the burnt playdoh) just ended up in the garbage.

    i will pick up some more silicone this weekend and try a new set of molds with the glycerin and acrylic paint. also, some rubber or vinyl gloves as well :)

    man, i gotta get an air freshener or something, god this stench is horrible :eek: :eek: :eek:
    chris
     
  22. Durasteel Corporation

    Durasteel Corporation Well-Known Member

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    "Youve taken your first step towards a moldier world."

    ;)
     
  23. Jayrcee

    Jayrcee New Member

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    Glad the tutorial was helpful :)
     
  24. AVE

    AVE New Member

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    This is awesome, Thank you for the information. I just started making molds for resin art. and my first mold of a skull sucked big fat harambee balls. but now i feel a little more confident that my next will be perfect, or close to it. Thank you.
     
  25. cavx

    cavx Master Member RPF PREMIUM MEMBER

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    Cauking silicone is air curing. In other words, it needs the moister in the air to cure, not heat. If you want to fast cure cauking silicone, you mix a rapidly evaporating liquid like acetone. You only need to mix at about 10 parts silicone to 1 of the acetone. It tends to break down the adhesive properties of the caulking silicone making less sticky. You will still need a release agent, but it will peel up off an item easier than it were applied with no additive.

    As the acetone evaporates, it gets cold and creates condensation which rapidly cures the silicone.

    Out of the tube, a 1" tube might take about 4 weeks to cure. The 10:1 mix will fully cure in the same 1" tube in about 2 hours.

    In truth, this route is OK when you need a quick fix, but based on cost of product, Vs results, and I would rather spend the extra on a proper molding silicone and know that I can re-use that mold over and over.

    You will also need to be in a well ventilated area to prevent the build up of that vinegar smell during cure. You don't get that with real molding silicones.
     
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  26. PoopaPapaPalps

    PoopaPapaPalps Master Member RPF PREMIUM MEMBER

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    :thumbsup This, so many times over.
     
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