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Casting With Plaster Of Paris


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I just received my first Hirst Arts molds today and was wondering just to start off with would plaster of paris be ok for making some?  I want to get something better but could actually get the plaster sooner and just want to play around with it.  Thanks for any info in advance!

On the Hirst Site they recommend against using it.

 

I tried using it years ago as a sheath for castle walls and it was terrible. I recognozie now the walls were probably too smooth for it to stick. Even dragons teeth (the obstacle not the wyrm dental implements) warped and cracked when made from plaster of paris.

 

I haven't tried molds with it except to cast limbs or masks helping visual artist friends. Those needed a fabric to provide structure.

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IMO PoP is fine to start with if you just want to mess around with it.  It's more brittle than dental plaster, so it will break if it gets dropped or handled roughly, but it's fun to play with. 

 

Your mix ratios will be different, as well as drying times, but you can still practice mixing, pouring, scraping and making a mess. :) 

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Thank you both I work at michaels so I get a discount is one of the reasons I was wondering.  As long as it doesn't do anything to the mold It can't hurt to play around with it.  Plus most of the things I am molding will be dungeon dressing (the armoire, tables, bar tops things like that) so it shouldn't be too bad) I'm just too excited to wait lol

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IMO PoP is fine to start with if you just want to mess around with it.  It's more brittle than dental plaster, so it will break if it gets dropped or handled roughly, but it's fun to play with. 

 

Your mix ratios will be different, as well as drying times, but you can still practice mixing, pouring, scraping and making a mess. :) 

Exactly. There's nothing wrong with PoP. Those of us who began using Bruce's molds back when he first started selling them can attest to the fact that PoP was the default material (probably because everybody knew what it was and it was easiest to get), and that Bruce himself recommended starting with it (his tutorials were - and may still be - based on PoP).

 

The people who "recommend against using it" are the ones who have a lot of experience with sourcing, buying, and using other materials. In short, the experts.

 

I use white hydrocal and ultracal because they are easy for me to procure, lighter than plaster, and stronger, too. But there's nothing wrong with starting with PoP. You'll learn a lot from it, and it's cheap. And if you mix it thick and handle your pieces well, there's no reason why they shouldn't last for a good while. Of course, the molds can take it with no problem, it's a gypsum cement, just like all of those other materials. And warping? On what planet does PoP warp? Maybe if you glued it to a thin piece of wood while it was still soft. But that would be the wood warping, and the PoP just going along with it.

 

Cracking? Yes, but it doesn't have to if you mix it right and let it dry completely.

Edited by Bruunwald
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That type of plaster is terrible for thin items less than 2-3mm thick. It's ok for bricks or 1/4 inch thick floor tiles, but they break easy if dropped from even low heights (like a table to the floor). I found that when I used wood glue to make low walls from bricks, I could pick up the wall section by a few bricks and they would snap right off around the glue lol

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POP is good to practice with.   Merlins magic is my material of choice.  It is expensive and expensive to ship but well worth it.    I would also strongly recommend making one of the back massager vibrating tables.  Used in conjunctionwith a good surfactant they will eliminate most air bubbles.

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Thank you for all the info I went in and bought some "Art grade casting plaster".  It wasn't the plaster of paris you get in a bucket we were out of that (it was on clearance argh!) but it came in a bag inside a box so maybe it is a little stronger but I doubt it lol.  Anywho tomorrow will mark the day that I join the ranks of the casters I am very excited!!

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There are tons of tutorials out there but my experience has been that PoP is a great starter material. It's cheap enough that you can get sloppy with it. 

 

Make it thick like cake batter. If you make it thin your pieces will be very brittle. 

 

The more solid an object, the better. Hollow containers and small bits tend to break trying to get them out of the mold. 

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PoP is a great way to start, but like others have chimed in, it does not work well in the details of the Inn and Accessories mold.  To get it thick enough for rigidity, it doesn't pour well into the cracks and crevices.  Oh, and those thin cracks and crevices?  Yup, PoP is just "soft" enough to crack or flake when trying to get them out of the molds.

 

I have tried PoP, Hydrocal, Hydrostone, Merlin's Magic, and Excalibur (from softest to hardest) of the casting materials.  After a few years of casting, I would recommend that you find Hydrostone (approximately $30 for a 50 pound bag).  Hydrostone can be found at pottery places and a few hardware stores (Ace Hardware used to carry it in my area, but not anymore :(  ).  Merlin's and Excalibur can (sometimes) be found locally, but is mostly a mail ordered item.  Garreco has several vendors (Clint's Sales in New England, Canyon State Dental Supply, and Patterson Dental Supply) all carry it.  I order from Canyone State once a year, order ten 50 pound boxes, and get the delivered price to be $46 a box drop shipped to South Carolina.  If you live closer, or further away, the shipping price changes.  But, ordering over 200 pounds gives way to discounted "bulk" shipping and you receive the items shrinkwrapped on a pallet instead of individual boxes.  I just cut the shrink wrap from the pallet, off loaded it box by box, and let the carrier take the pallet away with him...  piece of cake...

 

Any other questions, feel free to PM me.

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