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Thread: question about casting in plaster

  1. #1

    question about casting in plaster

    I have a question about casting in regular building plaster. My wife and I are avid mushroom hunters and when she gets back from vacation out of country I want to give her an aluminum cast mushroom (just to make her jealous of all the mushrooms I found while she was on vacation and I stayed home). I tried a few weeks ago, by placing a mushroom held by modeling clay at the bottom of a container and filing it with plaster. Didn't work, the plaster was to thick. So, I would like to try again by making the plaster more liquidy (is that even a word?). My question is, can I use normal building plaster? I have three huge bags of the stuff I was planning on using for a project in the house, but didn't like it because it dried up super fast (After 5 minutes it was pretty much already hard). Found a new brand that stays pliable for much longer, so I used that. So, can I use this or am I looking at an explosion waiting to happen. I've read about people using plaster of paris and baking it. I plan on leaving the mushroom in there for about a week until it disintegrates (A rather stinky process.. These mushrooms smell like rotting flesh when they get old). By then the plaster should be pretty dry, should I still bake it? Or should I not do this at all, risking any type of mold explosion?

    Cheers,
    Kyle

    BTW, here's a pic of the few mushrooms I found in my new secret spot after about an hour of looking. And, I myself hate eating mushrooms, but love spending some quality time in the woods looking for them.

    20170701_152005[1].jpg

    Also forgot to add that I have my first batch of green sand almost ready, but don't have a muller and don't know if it's good enough to use yet. Gonna try some homemade techniques later this week to try to mull it (also dont know if that's a word.. is that what a muller does..is mull things??)

    - - - Updated - - -

    Just re-reading this, I realized that if there were a mold explosion, it would be a double mold explosion with the rotting mushroom inside.

  2. #2
    Senior Member
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    I've not tried gypsom (although ironically I'm currently covered in it, my job plastering) I have used pop and despite cooking it I had a small explosion. Rasper uses pop with a grog, hopefully he will comment soon.

  3. #3
    @Peedee, as an of topic conversation and we are both in Europe, I'm curious if the same brands are available (probably not, it seems like everything I need or want here, I cant get). I forget the brand of plaster I originally got, but I was doing a job using Ceresit In 35. Loved the stuff! Granted, it was only for finish work, but it was so smooth and easy to work with.

    Kyle

  4. #4
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    The water must be burned out of the plaster. I have heard from usually reliable sources that if you burn plaster out at 500 F. in the kitchen oven, you can pour aluminum successfully. The water must be burned out. (Do not try this with bronze. You must burn out the plaster at much higher temperatures with bronze.)

    You must get the mushroom debris out as well. Make a two part mold so you can clean the mushroom out.

    You will probably have better success if you mix the plaster 50/50 with sand. It will not crack if you do that. Plaster alone tends to crack with heat.

    Make the plaster/ sand mix watery. Like Campbell's tomato soup.

    Richard
    When I die, Heaven can wait—I want to go to McMaster-Carr.

  5. #5
    I tried that method with PP, sand and a slow cook in the oven. Turned to a cracked crumbly pile of shit. Plaster of paris is not for this guy.

    Ceramic shell your shroom directly and burn it out. Pour hot metal, DONE! You'll get perfect results.
    Visit me: WWW.HandcraftedLanterns.com
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  6. #6
    Administrator Site Admin
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    To set up to make a ceramic shell investment for casting one mushroom seems a bit time consuming and expensive. It would also require building a high temp. burn out kiln as well. All for one mushroom?

    Better to buy a bag of the casting plaster that USG sells specifically for casting aluminum. Costs just a few dollars a bag. It's on their web site.

    Richard
    When I die, Heaven can wait—I want to go to McMaster-Carr.

  7. #7
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    Kyle, I use 'Thistle' brand for plastering work, It's probably the most popular in the UK. One thing to remember is the short shelf life of any brand of plaster, your setting up time problem may well have been associated with that. We don't keep bags for more than a couple of months to avoid that very problem. The other thing is use it fast when mixed.

    Excuse my spelling of gypsum in the previous comment, a long hard week followed by a few cold friday night beers! I knew rasper and others would come by with good sensible comments!

  8. #8
    Senior Member r4z0r7o3's Avatar
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    Mushrooms are sooooo delicate I think you need a more gentle method, something more like life-casting. An alginate or silicon box-mold, then make your resin or plaster mold from that. Finally, spray-paint it with some shiny metallic spray-paint so it appears like cast aluminum
    "Things that are complex are not useful, things that are useful are simple."
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  9. #9
    Moderator DavidF's Avatar
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    If your going to go through with it, why mess around?? http://www.kerrcasting.com/products-.../satin-cast-20
    A calm sea does not make a skilled sailor...
    http://thehomefoundry.org

  10. #10
    Thanks for the input guys, but anybody that has read some of my previous posts should know that I know absolutely nothing about what I'm doing. This would be my first casting ever. At this point I've been only melting and pouring ingots to get to know a little about what Im doing, learning my furnace, what works and doesnt etc, etc. I feel I am at a comfortable place to try casting. Half of the stuff mentioned I dont understand, or is not available to me where I live.
    If your going to go through with it, why mess around?? http://www.kerrcasting.com/products-.../satin-cast-20
    Out of curiosity I tried to check out with the cheapest smallest option available which was about 100$. they wanted to much info for me to continue, so dont know what shipping would have been. I did the same a few months ago when someone gave me a link for good refractory. I forget, but I think it was like 100-200 bucks for the refractory and over 1000$ for shipping. Dont have a credit or debit card, so it doesnt matter anyways... still just ridiculous..

    Anyways, it has been raining here like crazy and super warm with an almost full moon last night, so I'm going out early in the morning to find some specimens for my experiment (and keep in mind it's only July, cant wait for actual Autumn time). I plan on casting it in the plaster, mixed with sand as Rasper suggested (maybe a little less sand than 50/50). Wait a week or so and the mushroom should pretty much have shrunk/disintegrated to a size it's easily removable. At least I will have a mold. If I decided to pour alum directly into it or make a more permanent mold out of it. All I know is that before anything I need to go buy myself a new face shield. Wil keep you updated, and maybe take a vid to land myself on the wall of shame of Youtube winners.

    just a few more questions:
    The water must be burned out of the plaster. I have heard from usually reliable sources that if you burn plaster out at 500 F. in the kitchen oven
    How long do you recommend I bake this for?

    Finally, spray-paint it with some shiny metallic spray-paint so it appears like cast aluminum
    Maybe I will just spray the mushroom, and then when it starts to decompose it will be a way of saying "Thanks for going on vacation without me!". No, just joking. Originally I was supposed to go with my son, but it was my idea for her to go instead. I've been back many times but she hasn't in 12 years (due to visa problems). Plus, I think home alone is more of a vacation than the stress of traveling and vacationing.

    Cheers,
    Kyle

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