Islands Style

Episode II

Mixing Plaster by the Islands Method

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Picture yourself on a sandy beach, the early morning sun bathing your face in a warm blanket of golden light, palm trees rustle to the relaxing breezes.  The island natives dance in grass skirts around a huge fire they have built for the evening's meal of roasted wild boar.  Flames lick the pale blue sky and the air is scented with smoke and wild jasmine flowers.

This is the world of all those who mix plaster by the islands method.  It affords the opportunity to live free and ...

Oops, where was I?  Oh, I was daydreaming again.  Okay, back to the real world.  In actuality, you will have your hands deep in buckets of plaster slurry, swishing them around to break up the lumps of unmixed particles in the bucket.  A much more worthwhile endeavor than lying around on a pristine white beach, sucking down pina coladas.

Some Basic items you will need to start your plaster mold and casting business

You will need plaster. (No kidding. Really?)
The following types of plaster will be good for beginners to start with:  Casting plaster, pottery plaster, molding plaster or art plaster.  You could go to an art store and purchase a few bags of plaster, they sell it in 5 or 10 pound bags.  These retail marketers are a little too pricey for my blood.  Your best bet is to call building supply companies in your area to see if they carry plaster in 100 lb bags.   You'll get 100 lbs for the same price as a couple of small bags from an upscale art store.  Buy one or two of the 100 lb. bags.

If there is a ceramic hobby mold manufacturer in your area, you may be able to purchase a bag or two of pottery plaster from them or you can find a supplier of United States Gypsum plaster in your area by calling 1-800-621-9532.  Ask for a supplier of the plasters mentioned above.  They have reps on staff that are paid to help you set up your plaster casting business.  While you are on the phone to U.S.G, ask for the rep for your area.  They can be of tremendous help in deciding what plaster to use and how to use it.

You Need A Level Table
Mold shops use tables with marble slabs on top of them.  Some shops mount a marble slab about 3' x 3' on a 1" steel shaft so that it turns.  I have also used a Lazy Susan with a marble slab on it.  This makes mold making so much easier.   You just turn the marble to get to the back side of the mold.

Make sure your table is perfectly level.  If it is not level, everything you make will lean toward the peach orchard.

5 Gallon Bucket
This is a bucket of water for cleaning hands and tools.

A two gallon plastic pail or Tupperware Bowl
The plastic pail or bowl will be easy to clean.  When you are through pouring, dump out the unused plaster and let the remaining plaster in the bucket harden up.  You can then beat the bucket on the sides with a stick like Mama used to do to me to get me out of bed on cold winter mornings.

You can use Tupperware or other similar plastic tubs.  Just squeeze the sides together and the hardened plaster will come right out.  It is actually easier to clean buckets if you swish the plaster around to coat the sides of the bucket and let it harden rather than try to scrape and clean every bit out.

Mold shops use stainless steel buckets which cost $100 or more.  They wash the buckets out as soon as they are done pouring a mold. There are also buckets with removable plastic inner liners.  This saves wear and tear on the outer bucket.

If you want to wash the bucket rather than wait for the plaster to harden, dump out any remaining plaster into a box or an old plaster bag.  Fill the dirty mixing bucket half full of water.  Use a rag to wash all plaster from the sides and bottom of the bucket.  Dump this cloudy water into a waste water bucket.  After an hour or so all the plaster will settle to the bottom leaving the rest of the water clear.   Dump out the clear water and stop when you get to the plastery goo on the bottom.   Dump that plaster waste in the trash.

Apron or coveralls or clothes you wish totally ruined.

Water
About 5 gallons will do for our project.
The temperature of the water is very important.  It will determine how fast the plaster will set.  Water that is about 70ºF works well for average jobs.   Colder water slows the set, hotter water speeds it up.

Setting Additives
These secrets are handed down from generation to generation and no specific directions are given.  Furthermore, each type of plaster requires different formulas.   Experimenting is the only way to discover what effects these additives have.   You have to experiment to see how this will work for you.  When starting out, it's best to just use plain plaster.

Some old-time tricks to change the setting speed of plaster:
Old-timers would add a little alum to their water to speed up the setting of their batch.  Alum will also make the casts harder.

To slow down the set of plaster, the old boys would add some ammonia or stale beer to the water.  In the early history of the plaster business there was plenty of beer to go around in the shops.  Owners provided a pint of beer for lunch or allowed the men to bring their own.  Boy, the second half of the day always seemed so much better in those days!

Like any medicine taken to produce a cure, these additives may have side effects; most common is a weakening of the plaster.

Mixing by the Islands Method

and the gauging of plaster

Here it is.  Are you ready?  Estimate how much water it will take to fill your mold.  You actually only need 2/3 of that amount but mold makers always mix a little extra.  Plaster is relatively inexpensive and the problems caused by running short are not worth the few cents saved.  The first time your mold springs a leak or you realize you figured wrong, you'll be glad you mixed a little extra.

Plaster manufacturers recommend that you always weigh out the materials to achieve what they call the use consistency ratio.  That is the best way to get the optimum results from the plaster you're using.  After saying that, I'm now going to tell you how to achieve a similar ratio of plaster to water without weighing out the materials.   This only works for the types of plaster mentioned at the beginning of this article (Beta Hemi Hydrates).

Other plasters (Alpha Hemi Hydrates) will not achieve the optimum results by the islands method.

If you can work near an exhaust fan that is great.  A dust mask can be worn otherwise.  Put the amount of water that you have so diligently estimated you need into your mixing bucket. Never put the plaster into the bucket first and then dump water on top. Always put the water in the bucket first, then add plaster to the water.

With your dry hand reach into your big plaster bag and scoop up a hand full of plaster.  The plaster should feel smooth and free of hard lumps.  Wiggle your fingers and shake your hand to make the plaster fall through your fingers into the water in the bucket below.  This process prevents large clumps of plaster from falling into the water.

Keep sifting the dry plaster into the water with your hand.  Work quickly and spread the plaster all around the surface, evenly.  The process is similar to when Mama used to make a cake.  She didn't just turn the flour sack upside down and dump the flour into the bowl.  She sifted it in to get a fine, lump-free flour mix.   That's what you are going to be doing, sifting slowly and carefully.  Plaster should fall like gentle rain on the water surface, then sink out of sight.
Mama didn't want a lumpy cake.
You don't want a lumpy plaster mix.  Let's not make Mama angry!

Do not mix the wet plaster or disturb it in any way while sifting it in or this system of measurement will not work.  Keep sprinkling plaster into the undisturbed water.  Eventually you will notice little islands of plaster forming above the water surface.  When the islands stay at that level and get damp and do not sink below the water, you have the proper amount of plaster in the water for general purposes.

For specialized purposes, you may have to guage your plaster.

The Gauging of Plaster

This is an old-time term, but the process is still the same.  It is not to be confused with a type of plaster called Gauging Plaster.  The gauging of plaster refers to a method of determining whether you will have a hard or soft plaster cast.

When you are sifting your plaster into the water, you will notice that it will begin to settle just below the surface.  If you wait a minute, you will see clear water above the plaster.  That amount of clear water is your gauge.  You can leave 1/4" of clear water over the plaster to make a weak plaster mix, or you can bring the plaster exactly up to the surface level for a thicker mix and harder casting.   For a super hard mix, pile up the plaster in little islands and let them become thoroughly damp before mixing.

That's it.  You just used the islands method.  Try to control your excitement.

Depending on how long you have taken to get the plaster into the water (one minute should do for a small batch), let the mix slake (soak) for one to three minutes before mixing.

Mixing your batch of plaster

You can use your hand or  you can use an electric drill with a mixer attachment.  If you use your hand you may want to wear a rubber glove.  Plaster will dry your skin somewhat.  Hand lotion will help keep them in good shape.  At times my hands become so extremely dry and cracked its painful just to pick things up.   I find Jergens Ultra Healing Cream is about the best thing I've found so far.   If you find some other cream that really works, let me know.

When you use your hand to mix, you can feel every lump and judge the smoothness of the mix.  Batches over 2 gallons are not practical to mix with your hand.  A mixer blade attached to a 3/8" or 1/2" electric drill will be needed for larger batches.  Very small batches can be mixed with a cake spatula.  (Up to about 2 pints.)

The way to use the hand method is: place your hand flat down in the bottom of the bucket, spread your fingers wide, and shake your hand back and forth to agitate the plaster on the bottom.  Every once in awhile, use your hand to move some plaster from other areas to the bottom and continue shaking your hand back and forth.  Do not take your hand out of the bucket during the entire mixing process.  That would introduce air into the mix.  You will notice that the plaster creams after a certain point.   It takes on a definite change in texture.  It will have more body, feel smoother and creamier.  You must mix beyond this stage for the plaster to set properly.  Keep mixing for three minutes.  Yup, three minutes.  Seems like a long time, but that's what it takes to make a creamy, smooth mix.

You can mix longer than that, and you will have a harder, stronger casting.   Be careful not to mix so long that your plaster sets up in the bucket.  It's a game of chance once you go beyond three minutes.  How long can you go?  Mixes that you have guaged with 1/4" of water on top can be mixed longer.  Ones that you have piled up islands on the surface are more likely to set up before you pour all of the plaster out of the bucket.

So set your egg timer - ready...set...go!  Have fun.  Get plastered.

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