Plaster frustrations…

Arg… so you would think that it would be simple to find a local supply of one of the most common materials on the planet…

Gypsum is an amazing mineral. It is one of the softest minerals known, and is very easy to carve. Pounded into dust and mixed with water it can be poured into molds to cast just about any conceivable shape. “Plaster of Paris” is essentially gypsum plaster. It’s called “Plaster of Paris” because Paris happens to have a huge deposit of gypsum which has been mined and used in this way for over a thousand years. You are almost certainly nearly completely surrounded by gypsum as you read this since gypsum is the primary component of drywall, which is the most common construction material used to create interior walls in homes and office buildings. Prior to the adoption of drywall as an interior building material many interior walls were made from strips of wood which were overlaid by plaster to create an integrated interior surface. However, much of that plaster was actually lime based plaster with gypsum plaster added as a way to accelerate the setting of the plaster since lime based plasters take days or weeks to fully harden.

There is a wide variety of different types of gypsum plaster used in everything from home construction to fine arts to dentistry. “Dental plaster” which is used to create casts of teeth for the purpose of preparing crowns or bridges is a particularly high quality form of gypsum plaster which sets harder and captures finer detail than regular “plaster of paris.” But it’s basically the same stuff as plaster of paris.

A sack of high quality casting gypsum plaster is typically about a dollar per pound, so a 25 pound bag of it costs about $25. Lower quality plaster of paris in bulk can be even cheaper than that. Hobby stores generally carry plaster of paris at huge markups but even so it’s still usually pretty affordable at maybe $4 or $5 per pound.

With all of this understood you would think it would be pretty easy to go out and buy a bag of high quality gypsum plaster for casting items from molds. But you would be wrong. Or at least I have so far been unable to accomplish this.

I can buy a 25 pound bag of high quality casting gypsum plaster for about $25 online. However, that 25 pound bag has to be shipped to me at a cost generally of about $25, which essentially doubles the price of the plaster. I suppose you could say it’s still cheap at $2 per pound, but it drives me crazy that I can’t just go to a local craft or building supply store and buy a 25 pound bag of it. But I can’t seem to find anyone who sells it.

I have called half a dozen local dental supply companies to purchase a 25 pound bag of dental plaster. None of them can sell me a bag. Either they only sell to licensed dentists, or else they don’t actually have the bags on premise and they have it shipped (with shipping cost added) to the purchaser from their own supplier. Most building supply stores sell construction grade plaster which is intended to patch drywall or else to replace the older traditional lime based plaster to repair damaged moldings or wood work. That mixes into a mud-like paste, which works well when applying to a vertical surface, but which does not pour into molds very well.

So here I am, just a hundred or so miles from an actual TOWN named “Gypsum, Colorado” and I can’t buy a bag of high quality casting gypsum plaster without having it shipped from ARKANSAS at my own expense.

Sigh… what a world.


8 thoughts on “Plaster frustrations…

  1. Hmm… I’ve been to both Colpar locations many times and have purchased tools and game aids there, but I haven’t been there since picking up plaster casting as yet another time-wasting hobby… That’s not a bad idea, I think I will check them out.

  2. Well, all they have is the Lightweight Hydrocal, which is what I’m already using, and which is what all the hobby and craft shops sell. Somehow that stuff has cornered the market for hobby store sales even though it’s universally considered inferior to other products…. weird.

  3. So, it was suggested that I try “JoAnn’s” the craft/fabric store. Their online site listed a product called “Premium Casting Powder” or something like that at a reasonable price, but the JoAnns I went to did not have it in stock. However, there happened to be a Michael’s right across the street and I found a box of something called “ArtPlaster” on their shelves, which is also billed as a “premium casting plaster.” It was $6.50 for five pounds of powder. That’s getting pretty close to the bulk rate cost of the 25 pound bags BEFORE you add shipping. So I bought a box and did a simple casting of a column and a mushroom man. Both came out pretty well. When mixed it is significantly thicker and stickier than the Lightweight Hydrocal, but it still seemed to pour OK. The stuff takes a full day to cure, but it cures enough for demolding in about an hour, which is comparable to the Lightweight Hydrocal, and the result feels much more robust. It’s probably twice as dense as the Hydrocal and it seems to be harder, although without deliberately breaking samples, I can’t be sure. But it FEELS more sturdy.

    I am considering mixing the two to see what the result would be… I will probably try that today.

  4. That….website….nnnnngggggg…….
    You should have included a warning — I almost didn’t survive! As it was, I had to quickly throw diet coke in my eyes to escape the horror.

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