Plaster, Anyone?

Here’s a big-little update on the project I’m working on for my sculpture class. In my last post I kinda talked about designing the piece and building an armature, and now I’ve moved on to adding the plaster.

The plaster process is a little tricky, because the plaster has to be just the right consistency in order for it to work properly. Typically I like to measure things (like ingredients) just to prevent making mistakes, but in this class, there’s no such precaution. “About so much water, and then some plaster,” my teacher instructed. Right. About so much water and then some plaster….. This particular teacher takes the “learn from your mistakes” method of teaching. He will explain something once, and that’s that. It’s not like he won’t repeat himself if you go and ask him to, because he will, but he’ll give you a little bit of a time about it and ask, “weren’t you listening the first time?” … I do listen, I actually take notes (shocking I know) but, if I knew everything, I wouldn’t be here. Being a student is a real pain some days, but you’ve got to learn someplace…

So, after hassling my poor teacher to no end, I’ve almost gotten the mixture down. It’s about so much water, and then some plaster. 😉

You start by putting water in a bowl (we’ve been using rubbery bowls from a feed supply store, because they’re flexible enough not to break when you clean them up later.) You always start with the water first. I’m sure there’s a reason, I just haven’t puled it out of my teacher yet, and then you add the plaster by handfuls. Our plaster comes in 50 pound bags of powdery wonder. You sprinkle the plaster into the water, but you do not mix it. As you watch, the plaster will begin to slake. Slaking is this very interesting process where the powder plaster basically turns into liquid rock. As you add the plaster, it will begin to absorb all of the water and turn a sort of greyish color. As you get close to having the right amount of plaster to water, you will be able to see the plaster slake and change color. It will look something like a cracked-mud desert that’s getting flooded…yeah, that’s a lousy description, I know. I’ll grab some pictures next class and maybe that will help. The dry, crumbly plaster will begin to look crusty and then mushy… after it looks pretty mushy, you can mix it a little bit to get out the remaining lumps. You don’t want to mix it before this other wise, as you add more plaster, it won’t slake properly.

At this point, you are ready to begin putting plaster on the armature. Using strips of burlap, I dipped them in the plaster, coating them with the mixture and slicking off the excess with my fingers (over which I was wearing surgical gloves because I don’t like icky, slicky, sticky stuff…yeah, my teacher got a kick out of that…) anyway… I covered the base of my sculpture with the burlap/plaster, making sure to leave an opening underneath so that the inside is hollow (this is important for later) and waited for it to set.

Setting is what happens when the plaster begins to dry. Complete drying can take days depending on the thickness of the plaster and humidity/weather air conditions in your space, but setting usually happens in 15 minutes or less (at least in my limited experience). You know that the plaster is set when you can press your finger nail into it and leave a slight mark, but nothing major. (As a side note, if you use warm water, the plaster will set faster…faster plaster, faster plaster, faster plaster…say that ten times fast!) If it begins to set too quickly, though, it will start to get too thick to work with, and you’ll probably have to throw some of your plaster away because you can’t use it fast enough (a matter of minutes in some cases.) So, only a master can plaster faster! (OK, not necessarily true, but I like to rhyme things!) 😉

Once you have the burlap/plaster layer set, you can simply add layers of plaster to build up your sculpture. BUT! Unless you are adding more layers at the same time (as it sets) you will need to soak your sculpture in water before adding more layers. This is because once plaster has dried more-or-less completely, new layers of plaster won’t stick…well, they will appear to stick when you put them on, but be not deceived! As they begin to dry, they will let go of the layer that was already dry, and break off, leaving you back where you started, utterly disappointed. You just need to soak your sculpture in water until the dried plaster on it has absorbed all the water it can…that’s a little vague, but that’s what he told me. This is why you want to make sure there is a decently sized hole in the bottom of your sculpture, so that after you soak your sculpture, the water can easily get out and you wont have to wait for it to drain. If you submerge your sculpture in a bucket of water (provided your piece is small enough) you can usually tell that it has absorbed all the water it will once air bubbles stop surfacing in the water. After that, you’re ready to add more layers of plaster.

And that’s where I’m at, layering my plaster and trying to make my sculpture look as smooth and finished as possible.


Wow, this was kind of a long post…if you have any questions, just slap ’em in the comments! I may not have an answer, but I bet I can annoy it out my teacher if I have to! 😉 He and I are gonna be friends by the time this is over, despite how hard he claims to be! Either that or he’ll just be really glad to see me go…



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