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Basic Plaster Craft Instructions
Part I - Mold Preparation
By Bob Sherman
Plaster craft is a fun hobby which allows you to turn a few pennies worth
of materials into beautiful wall hangings and sculptures. Although there are
several techniques used for plaster casting, in this tutorial series we will
be discussing the simplest method - making flat back plaster castings in open
top molds. Most common plaster molds are this style, but chocolate molds also
work well for plaster. Avoid two piece or 3D molds until you have some experience.
PLEASE NOTE!! - Plaster crafting is fairly safe if you observe these safety
rules when mixing plaster. Once hardened there is little or no hazard from
handling plaster items:
- Plaster is very alkaline and and exposure to high dust levels may irritate
the skin, eyes, nose, throat, or upper respiratory tract. Wear a dust mask,
eye protection, and rubber gloves when mixing plaster.
- Do not wear contact lenses when working with plaster.
- Plaster generates a lot of heat when setting - never use plaster to make
casts of body parts.
- Keep away from children or pets.
- Other safety precautions may apply depending on the plaster product you
use - read the directions.
Plaster is used throughout this article to describe casting products containing
mostly plaster of paris. The two most common are plaster and hydrocal.
- Plaster is generally 100% plaster of paris and is called a variety of
names depending on the manufacturer. These include: Plaster Of Paris, Casting
Plaster, or just plain Plaster.
- Hydrocal is a mixture of plaster of paris and portland cement and is called
a variety of names depending on the manufacturer. These include Hydrocal,
Hydrostone, and Ultracal. Typically hydrocals are 3 times stronger than
plaster and more dimensionally stable. For castings with thin areas hydrocals
are a good choice.
Plaster Casting Supplies
The following plaster craft supplies will be needed to follow along with
this series of articles. Clicking on the item name will bring you to that
item's page with a full description and ordering information.
||A medium sized mold of your choice. A suitable chocolate
mold may be used if you prefer.
||A flexible mixing bowl simplifies cleanup, but you may use any plastic
||This requires a power drill to use, but makes blending the plaster
much easier. If you don't have a power drill, a potato masher may be
used to mix the plaster manually. For very small batches you could even
use a stick.
||Optional, but recommended. This will help eliminate air bubbles in
||We sell these to accommodate our customers, but you may wish to source
it locally since the shipping cost is high due to the weight. Plaster
may be found in most home centers and hardware stores. Hydrocal is much
harder to find locally.
||Optional. Plaster can be mixed by guesswork, but a scale will allow
good repeatable results every time. I use an Ultraship
55 scale for most plaster work, but any moderately accurate scale
that can weigh in 1 ounce increments should suffice.
||If making wall hangings you will need some hangers.
||Optional. Useful if you desire to color the plaster without using
|Rice Bag or Sand Box
||Most plaster molds do not sit flat and it will be necessary to support
them. More details on this will be explained below
||I use a standard utility knife but any semi sharp knife will suffice.
||To support hangers if necessary.
Cover your work surface with newspaper or a piece of vinyl. As you can see
from this photo plaster casting is a bit messy so it is important to protect
Inspect the mold to make sure it is clean and dry - any dirt will show up
on the finished casting.
Most molds will not sit flat on the counter so it is necessary to support
them for use. I find the simplest way is to use a zip lock bag with a few
pounds of rice in it. Rice bags are easy to pack and store when not in use,
and made with common materials most folks have handy. A box of sand works
well also, but is more difficult to make and store when not in use.
The surface tension of the water in plaster tends to trap air causing pinholes
in the finished casting. Airid
is a product designed to break that surface tension, minimizing the chance
of trapped air. Spray or wipe a thin coat of Airid into the mold (optional).
Wiggle the mold down onto your rice bag or sandbox until it appears level.
You are now ready to begin mixing your plaster.
Click Here To Continue To Part
2 - Mixing Plaster
Disclaimer: The information presented here is accurate to the best of my
knowledge and common plaster crafting practices as of the time of this writing
- September 2006. The author and the publisher accept no liability for the
use or misuse of any of the information presented in this article. This article
is presented for informational purposes and is used at your own risk.
Author: Bob Sherman
Publisher: Bobby's Craft Boutique Inc.
This article is provided free of charge for use. Candles may be made and
sold using this design royalty free.
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express permission from Bobby's Craft Boutique Inc. with the following exceptions:
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may use this information without permission for printed materials provided
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