The Importance of Communicating with your Plaster
This is the Age of Communication. It is the most important skill that we can develop today, or so I'm told.
A master mold maker once told me that his uncle was so good he could make plaster sit up and talk.
I've been working at it real hard ever since and I still can't get my plaster to say "peep." Oh sure, I've heard the voices everyone else hears. You know, Elvis singing in the fillings of your teeth and all that. But as for my plaster talking - nada, zero, nothing. It just won't communicate with me.
Since I've been looking into this whole field of how things communicate, I've noticed that there are a lot of clever messages on signs and decorative wall hangings. There should be a market for plaster wall plaques with original sayings or art work on them.
We've learned how to mix plaster. So let's use that skill to make our own original wall plaque. We'll learn about the tools and materials of the trade in this very basic project.
Tools of the Trade
Materials needed for this project: Mold boards, soap, 3" oval brush, natural sea sponge, 14" scraper, water clay, (1" to 2" round brush - optional)
Mold Boards
For this project we will need four boards - 1 inch x 2 inches x 12 inches, more or less. They will make up the form to constrain the plaster in a rectangular shape. We can call this shape a blank or a bat, which we will use to reverse carve our design.
You will need other size boards as your mold making business grows.
Mold shops keep an assortment of several dozen mold boards on hand for use in making plaster molds and R T V (room-temperature, vulcanizing) mold making material. The boards are covered on one side with formica. A good source for this formica-covered plywood is your local custom-kitchen fabricator. They cut holes in their counter tops to drop the kitchen sinks in. You may be able to talk them out of these scrap hole blanks for little or no money. I vote for the latter.
Make your boards in matching pairs from these counter-top scraps. A dozen different sizes will be good enough for a start.
An alternative to the formica-covered mold boards would be
3/4" birch-faced plywood - finished on one side. Coat the (birch) finished side
and the edges of the boards with 3 coats of clear polyurethane, according to
manufacturer's directions.
Next, wax the boards with a good quality paste wax. Buff up to a nice luster between
coats, then apply mold soap in a normal manner.
Mold Soap
If this is a one-time project for you, and you're not planning on going into business, you do not have to invest in mold soap. You may use petroleum jelly on your mold boards. It's a little too messy and inefficient to use on a professional level, but it will do as a make-shift release agent on your mold boards.
Rub the petroleum jelly well into the wood, so that all that is left is a thin even coating on the surface.
What Is Mold Soap?
Mold soap is not the same hairy, green goo you find under the soap dish when you clean there because the in-laws are coming over. Ordinary soap is not the same thing as mold soap. Mold soap or potter's soap, as it is sometimes called, is a very special soap. It won't clean anything. It is made of pure potassium oleate in a 75% concentration. It can be purchased from Crystal, Inc. PMC. It is a fairly safe product to use Be sure to wash it off your hands before it dries on them. Don't get it in your eyes - which happens to everyone at some time or other. You'll run around the shop yelling for awhile, but trust me, this too shall pass. You can try splashing water on the affected eye. It will give you something to do while you are thinking about what blindness will be like. In five minutes the episode will be over and you'll be back to work. Soaping much more carefully this time.
When you receive your mold soap, it will be in concentrated form. Upon prying the lid off the pail, you will be staring at a honey-brown colored, thick sticky mucilage-like goo. A five-gallon bucket of the stuff costs about $56.00, plus shipping and handling. To make it usable, scoop out a coffee can full of the brown, icky paste and add 4 to 5 cans of warm water to it. At this point, some people let it soak for a few days to soften up. I use an electric drill with a paint mixer attachment to blend it. Mix until creamy smooth.
You can borrow the family crock pot ( not the family crack pot) - we're talking about the electric device to heat food, for storing and warming your soap mixture. After all, this is a money-making venture and some sacrifices will have to be made by the entire family. That line didn't work for me, but you are free to give a try at your house. (Caution: Be prepared to dodge flying household implements if you accidentally forget to ask first.)
Scrapers
The scrapers used in mold shops are a straight piece of steel approximately 1/16 inch thick. I get mine from a steel rule die shop. These people make cutting dies for cardboard boxes. They are about 2 inches wide and range in length from 6 inches to 18 inches. I also have many small scrapers made of the same steel rule die material that are 2"-3" long. Some are ground to various curved shapes.
Clay
There are two types of clay used in mold making, oil based clay called plasteline and a water based clay. We use the water clay to seal around our mold forms. It can be purchased in hobby shops. It is similar to the kind of clay used by potters in hand-thrown pots.
Brushes
Mold makers brushes are made of china boar bristles. I guess they get Chinese pigs and pluck the hair out of them. I don't know. The 3" oval brush is the most popular one used. 1" and 2" round brushes are used occasionally.
Soaping Up
Soap and Plaster Don't Mix - That's a Good Thing
The traditional implements for soaping up are: a 3" round, natural bristle brush (china boar bristle) for applying the soap, a large, round natural sea sponge (the kind used for washing a car) for wiping off excess soap, a 1" to 2" round, natural bristle brush called a "take-off brush" may be necessary for removing soap from fine detail and tight spots, a rag on which to wipe the small brush.
Use the large brush to apply a generous coating of soap, thoroughly soak the piece, then wipe off all the soap that you possibly can with the large sea sponge. You should prepare your sponge ahead of time by dunking it in your mold soap and squeezing out as much as the liquid as possible. Use the smaller brush to go over the piece to get out any remaining puddles of soap. Let the item dry a few minutes. Sometimes I use a hair dryer to speed this process, brushing and blowing at the same time.
Wipe the small brush on a cloth or paper towel frequently to keep it dry. Keep going back and brushing all the wetness off the piece. If you leave pockets of wet soap, it will inhibit the cure of the plaster in that area.
That completes the first coat. Go back and do the whole process again. Apply soap. Sponge it off. Use take-off brush to remove smallest pockets of soap. You must put on 2 to 3 coats. If you do not put on enough coats of mold soap, water from the plaster mix will seep through the soap layer and cause your casting to stick. As further insurance against sticking, you can apply a coat of lacquer or shellac to a mold before soaping. Do not touch the surfaces of the mold where you have soaped. This will cause the plaster to stick wherever you touch.
Note: Bone-dry plaster molds should be placed under water for 15 to 30 seconds to thoroughly wet them before soaping.
Some Bats Eat Bugs
Some bats are anemic white slabs that just lay around on your workbench and do nothing.
We'll be casting a plaster bat, approximately 1/2" to 3/4" thick. It will be in the shape of a rectangle, approximately 12" x 10".
Soap up your plaster tabletop (use PAM, if you're not one of us professionals). Also soap up the 4 boards that you cut earlier. Take the boards and place them with the 2" wide surface flat on the table. Arrange them so that they make a rectangle, approximately 12" x 16" outside dimensions. The inside dimensions will be roughly the 10" x 12" form for the plaster bat.
You must seal around the outside perimeter of the boards with water clay.
Roll your water clay into ropes, about 1/2" in diameter and 12" to 18" long. Pack them tightly around the outside of the boards. This will keep plaster from escaping its wooden corral. It will also hold the boards in place. So use plenty of clay to hold things in place. Use a small square on the inside of the form to true everything up.
Estimate the amount of water it will take to fill the cavity you have created with your boards. That is the amount of water to use for your mix. Put that amount of water in a bucket (no kidding, I was going to dump it on the floor). Sift in your plaster. You can use white art plaster, casting plaster, pottery plaster or molding plaster. These are beta hemi-hydrates and will be soft enough to do the reverse carving for our plaque.
Gauge up your plaster as a normal mix (described in Episode 2).
After 3 minutes of mixing, pour your concoction into the form to a depth of 1/2" to 3/4". Pour slowly in a thin stream - not from half a mile up in the air - but close to the marble. We want to avoid splashing and bubbling. Some people use a tin trough to flow the plaster smoothly into the mold or form they're pouring. Stick a ruler in it to check the depth. Shake the workbench to remove air bubbles. And you're done. Whew!
If you have done a good job of leveling your workbench, your plaster bat will have an even thickness from end to end.
You will notice that the plaster goes through several stages on the way to becoming a useable, rigid piece of plaster.
You may see a thin layer of clear water on top of the cast. This is normal. It will re-integrate with the plaster as it sets. Watch this water on top of the cast. As it is reabsorbed into the plaster, the stiffening process begins. You will see the glossiness of the surface turn hazy. The plaster is the consistency of yogurt at this point. It may take 10 to 15 minutes to reach this stage, depending on the temperature of your water and the kind of plaster you're using. In a few more minutes, it will be hard enough to remove the boards. Lightly touch the surface to see if it feels firm. The plaster can be carved very easily at this stage. It is like butter. Beginners should let the plaster set up completely before removing the boards.
The plaster will start to heat up. When it reaches maximum heat, and starts to cool, it is safe to remove the boards. If you have a steel scraper, you can scrape the surface flat at this time. Do not try to pry the plaster bat from the marble at this time. You will find that it is stuck like glue to the marble surface. Let it cool a bit. Moisture will form underneath the plaster bat and cause it to self-release. It will lift up as easily as green beer on St. Patty's Day. There's no substitute for experience in these matters. (Plaster casting, not the beer drinking.)
Your efforts should have rewarded you with a beautiful, white plaster bat, a blank slate on which we can carve anything our crafty little minds desire.
Let's put it aside and think of what to carve on this marvelous little pristine rectangle you have created. Perhaps the muses will whisper something in our ears. Right now, Elvis is talking too much for me to hear anything. I have to go anyway. The nurse is here with the medication cart. They say I'll be allowed out this weekend if I stop wearing my underwear over top of my Levis. If that's true, I'll see you next time. Maybe. I like to show off the sequins.
Okay, I'll tell them. "The King" says, "Thank ya verra much for comin. Ya'll be sure to go out and git plastered now, hear?"
There. I told them. Are you satisfied.
I guess so...
Elvis has left the building.
