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Mistakes are how we learn

Discussion in 'Molding and Casting' started by montana art, Feb 18, 2009.

  1. montana art

    montana art New Member

    407
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    N.C.
    Well I have been wanting to cast a mold from an Oak slab about 14 x24 and read about mixing silicone with a little acrylic paint to make it set. The article said it would set fast but man that stuff turned into putty like bread dough in about three minutes. I put around one ounce of paint to four tubes of silicone, mixed with drill never made it out of container before setting up. How little is is needed just a few drops per tube? :-[
     
  2. So was the problem that it set before you had a chance to use it? I usually work in small batches, mixing about a tube of silicone at a time (and about a tablespoon of acrylic paint), applying that, letting it cure, and while it cures I mix up the next batch of silicone and acrylic, apply it the stuff that's setting, and keep going until I have the whole thing coverred. I also mix it by hand.
     

  3. RF

    RF Member

    ???I have been thinking about giving that a try. Any chance you can post some pictures?
     
  4. Ravenson

    Ravenson New Member

    you know I have never had much luck useing tube silicone and paint but reading this makes me think I may have been using too much paint. humm Maybe I will have to try it again.

    Jeff
     
  5. Gooter

    Gooter My Taxidermy Assistant

    I'll add my 2 cents here but my disclaimer is that I am totally a rookie with molding/casting. That said, I've been doing a BUNCH of molding with silicone caulk - mostly heads and legs for my lambs and goats, so I'll share what I have learned.

    I found that you can play with the cure time by changing the amount of paint you add. I tend to mix anywhere from 3 to 5 tubes of caulk at a time in a plastic container, and I mix it by hand. (OUTSIDE! the fumes are toxic!) I always use clear caulk so that I can see easily how much of a ratio I have. I use less paint (the catalyst) when I have more silicone so that I have a longer work time. You still need to work fast, but it gives enough time to do what you need. If I have a head or something that I want to be able to pull out of the mold faster, I add more paint. If you have mixed a batch with clear caulk and it's really colored heavily, you won't have much work time. If it's almost a bit translucent, you'll be fine. Got to mix thoroughly tho!

    I keep a container of dish liquid/water handy, and wear gloves. I get all the caulk in the mixing container, and when ready to go, add just a bit of paint. 1 oz sounds like a LOT. I use maybe a teaspoon worth for 4 tubes of caulk. I mix quickly and thoroughly, then quickly pack it into the molding container or onto whatever I mold. With gloved hands dipped in the soap/water mix I pack it, shape it and tuck it - put it where I want it. Then I leave it. Also, to help w/ cure time (as per the archives) I lay a wet rag over the top to speed curing.

    I kind of figured out the ratio by accident. But now, there's no questioning! The caulk really does work great!
    Eileen
     
  6. I plead ignorant here, but how much is a tube of clear silicone caulk? You will get better physical properties using GI 1000 Base Trans and GI 179 Clear activator. It is transparent in color and can be tinted. A 2Lb kit of it, which I'm guessing might be in the same ballpark as 4 caulk tubes, runs about $30-35$. Is it in the ballpark for cost with improved strength or is it still way too expensive? I'm only curious. Believe me when I say I used to use the caulk methods years ago when I used to work at a parts making plant. Also, the addition of water will make it "kick" really quick as well. Just a little dab will do ya.
     
  7. Gooter

    Gooter My Taxidermy Assistant

    I get my caulk at Walmart. $2.77 ea.

    I personally will be stepping up to 'the real world' at some point, but for me, getting the process down while using local materials is not only a necessity at the moment financially, but also I need it in order to get familiar with what I'm doing. As the thread title says, mistakes are how (I) often learn. Pinches less when the investment is less. Take longer, process more complicated? I think yes. I'm not complaining. I speak only for meself tho!
    Eileen
     
  8. I understand. Caulk is a wonderful thing. We used to use a ton of it.
     
  9. Be sure the caulk is 100% silicone.
     
  10. Jim F.

    Jim F. Let's go Fishin!!!

    I really like using the Silicone Caulk for molding bird heads, fish heads, fox, coyote, bear noses. It makes excellent small molds very cheaply. And probably the best part about is, I can make a mold and cast the part all in less than an hour.
    For molding fish, I use pour on silicone because I'll want those molds for many pulls.

    As far as cost, I pay $1.99 per tube of no name, 100% silicone. It comes up to around 1/3 the price of Smooth-On silicone in the 2gal. kit.
     
  11. Polymer Guy, Jim... it's funny that you mentioned it. The last large molding project I took on required nearly 50 dollars worth of silicone caulking, Silicone Caulk for me is around $5.00 a tube up here. it's getting very expensive for large projects, and considering how many tubes I use in one project I am starting to wonder why I don't just advance into the more technical world of silicones and mold making supplies. Honestly, I'm intimidated by the huge number of mold making materials out there, and I hesitate to invest a lot of money in a mold material that I havent tested before, and am unfamiliar with. :-\ Maybe I'm just buying the silicone from the wrong place? I go to Home Depot.
     
  12. Bonnie, PM me.
     
  13. Bonnie, Is this for a large sculptural piece?
    If so I would use rtv silicone over caulk. it depends on your casting material, but if its going to be cast in wax I would use RTV over urethane rubber.
    Polymer guy will be able to set you up.
    Its easier then you may be thinking.

    I use caulk on Rocks, and wood, and occasionally on mouth plugs for fish replicas, other wise I use RTV rubber.
    As for where to buy it go to walmart. its about 1.99 a tube here.
     
  14. fishdude

    fishdude New Member

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    0
    Has anyone ever used this method along with a pourable silicone. In other words, use a thin layer of pourable silicone over whatever you are molding to minimize surface air bubbles etc. Then, when that kicks use the cheaper tube silicone to do the buildup. I wouldn't use the tube silicone for a production mold but for a quickie waste mold it might be the ticket. I'd be interested to hear if anyone has tried it.
     
  15. The issue with that is quality rtv silicone doesnt shrink, but caulk does. Its very slight but that shrinkage will cause the RTV to buckle ruining the mold.
     
  16. PolymerGuy - I'll definitely be contacting you.

    Josh - Thanks, I'll have to check Walmart, we don't go there often... but there's a home depot or lowes around every other corner over here, so that's where I usually end up. But ifwalmart has silicone caulk at half the price I'll be pretty happy and definitely check it out. And as for scale of my projects, they occassionaly get on the large size (if it's a small project, I like RTV silicone). The wax does cast into the silicone caulk very nicely and I can use the mold again and again, which is why I like it so much.
     
  17. Cool! what type of wax are you pouring into it?
    I have always had an odd reaction on the surface when I cast into the caulk molds.

    Glad to see you didnt freeze on your hike ;D
     
  18. We try to reclaim it... so it's never a homogenous solution. I'd say it was a combination of Victory Brown, and a new white white microcrystaline wax we are using to replace the victory brown, and probably more red sprue wax than anyone intended lol. If you are getting a weird reaction are you using a separator? I don't normally have to.. hmm.. Nothing I've ever done has a smooth surface, so I might not be noticing it. Or are you referring to a very a very very tacky and sticky surface? That happens to me a lot. =/

    Yeah I survived the hike. I actually walked all the way there, only to realize I forgot my keys. :) So I made two trips. Pretty awesome huh? At least by the second time out the snow had stopped, so I got a head start on clearing off the car. woo!
     
  19. I use a pure red victory wax with a little parrifin added. for strength.
    I am really picky about the surface so that stickiness bugs me, and sometimes if I dont melt the wax once and let it cool to remelt it it leaves odd bubbles.
    I think its the wax more then the silicone tough.