Introduction:
With the facade projects in full swing I am trying to improve the basic forms I use to make the plaster casts from.
I am used to working with basic silicone forms. Although they work well they are limited in their use.
A basic form is perfect when you are making a series of projects with more or less the same shape.
The more I move away from the basic form, the more work there is to remove excessive plaster.
Making a temporary casting form out of silicone is time consuming and the material is expensive.
This is the reason I am startint with temporary basic forms.
Materials used:
The basic material for a temporary casting form is Styrodur.
This high density foam is not only great for modeling but also for making these forms.
Due to its structure you get nice smooth casts.
Other tools you need: foam cutter, ruler, hobby knife, wood glue and some pins.
picture tools
Making a Basic Temporary Form:
The most basic form is one that only produces a flat surface with a specific outline.
In this case, I use a piece of Styrodur as a "base layer" and pin the form to it.
The form consists of one or two sheets of Styrodur (for depth) in which the form has been cut out with a hobby knife
or foam cutter. The cut out is now pinned on the base layer.
I use pins, sticking them through the foam at an angle (not straight down).
This gives a bit more support to the form.
A basic form does not have to be glued. Simply cut out the desired shape,
pinned to the base layer, and cast the plaster in. The form might leak a bit, simply add an extra pin.
Making a more detailed temporary form:
Working with the casts out of these forms is fine but now it is time to bring these temporary forms to the
next level. In this case I will try to put as much detail in the form as possible.
Making elevated parts in a form sounds easy, but you might get mixed up more than once while building the form.
It has to be built up in layers and the form has to be the negative of the object that you want to cast.
This means that areas that are sticking out in the cast lay low in the form and areas that are laying low
in the cast stick out in the form.
Another thing to be aware of is that when you want a specific part to stick out in the final cast,
then make the area slightly bigger than the result your aiming for. In this case it is better to remove
a bit of plaster than finding out that the area is too small.
The same goes for parts that lay low but then in a reverse way. If you make the shape of a window in
the temporary form then make it a bit smaller than the result you are aiming for.
The reason to work as explained is the fact that when you get a cast piece out of its form you might get a
tiny piece chipped off, not as sharp, or air bubbles along the edges.
If you have some extra plaster to work with you are able to avoid these problems.
The basic temporary form can be pinned down on the Styrodur surface and you can start casting.
Working with more detailed temporary forms you must glue the layers on to the layer(s) underneath
in order to prevent parts from shifting and/or floating up.
In this case the edges of this form can still be pinned down. It is the inner structure of the form
that has to be glued.
I use temporary forms for one off castings. After use, I throw them away.
If the form is not too complex and the cast is removed with care, then you may use a temporary form more than once.
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