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The
Surprising Benefits of Casting with the FORTON MG System
By
E.J. McCormick
ArtMolds
Sculpture Studio
Introduction.
What do you get when you marry the best parts of plaster casting
to the best parts of epoxy and fiberglass? An ultra strong, very
hard, weatherproof, odorless, and most importantly a non toxic
material casting system that one can sculpt like plaster called
the FORTON MG Casting System – sometimes referred to as FMG.
FMG consists of a gypsum
plaster modified (hence the abbreviation M.G., for Modified
Gypsum) by the addition of plastics and fiberglass. The system
involves mixing precise amounts of several products, including
Hydrocal FGR-95 from US Gypsum or alternatively, Densite HS from
Geogia Pacific (both are gypsum-based cements); dry melamine
resin powder; a hardener; a liquid polymer called Forton VF-812,
and; fiberglass. These various ingredients are the base to which
aggregates, colorants and metallic powders may be added; in
which the latter, though somewhat pricey, simulates the look and
feel of metal.
Hiram Ball of Pittsburgh, who
is arguably one of the most knowledgeable persons there is on
FMG application, first introduced me to the process. Then a
short time later I was privileged to take a lifecasting class
with Mark Prent at his Vermont studio and discovered that he too
had switched to FMG, after years of working in epoxy and
fiberglass, for most of his lifecasting work. It was there that
I became a believer and have used FMG extensively ever since.
FMG is compromised of a
glass-fiber reinforced gypsum (hydrocal) system. It was
initially designed for outdoor-architectural work, but the
material can be utilized for interior or exterior sculpture.
What convinced me was not only was it simple to use after one
mastered its mixing proportions, but most importantly it was
non-toxic.
Advantages of FMG.
The FMG Casting System is odorless and easy to use for solid and
hollow castings. The casting method is essentially the same as
that used for casting in polyester resin and fiberglass. But,
Forton is easier to work with, so a casting made with this
material takes less time to complete. Repairs are a snap as the
material can be worked with your plaster tools so that patching,
sanding and finishing are all easier on a casting made of Forton
than on a casting made of polyester resin or epoxy.
An additional advantage is
that, unlike polyester and epoxy resins, Forton may be cast
directly into an alginate mold to produce extraordinarily fine
sculptural detail. From the standpoint of health and safety the
Forton casting system is considerably less hazardous when
compared with polyester resin or epoxy casting.
Those of us who use FMG believe
it an ideal medium for lifecasting as it is lightweight and thus
a great choice for sculptural wall hangings. It is also
weatherproof so a casting can be displayed outside. FMG has a
rapid mold cycling time of 60 to 90 minutes –and drying is
even faster by adding an accelerant. Aggregates and pigments can
be added to the wet mix to achieve a natural stone look. The
look and feel of foundry casting can also be achieved through
the cold casting method of adding metal powders. Once FMG and
metal powder mix has dried the surface will take on the same
patina of 100 percent metal. The surface can then be patinaed
using foundry etching acids, or be polished to a high shine.
Another advantage that casters
will like is that FMG can be worked as if it were simply plaster
using plaster rasps and wet sandpaper. However, the material
allows better control and more flexibility than plaster.
Speeding the drying Time.
The demolding time without a drying accelerator ranges from 1
1/2 to 2 hours. With an accelerator one can shorten the time to
as little as fifteen minutes. Try that with just plaster or
epoxy. The accelerator can be found at the local garden supply
store in the form of aluminum sulfate—a fertilizer. Just mix
one pound of the substance in one gallon of ordinary water. The
amount of accelerator used depends on both the age of the
hydrocal gypsum and the ambient temperature. Though a formula is
offered below, I found that trial and error worked best. That is
adding a little to the wet mix and seeing it beginning to harden
as it was being stirred. With the first few squirts of
accelerator into your mixture nothing appears to happen. Then
another squirt or two and suddenly the mixture quickly thickens.
So be cautious in your application so you don’t wind up with
hardened FMG in the mixing bucket rather than in your mold.
Release agents.
FMG is very versatile in that it can be used in a wide range of
mold materials. Latex and urethane molds need a release agent.
But silicone molds do not. A note of caution though, I learned
this the hard way-- typical release agents are fine, except that
silicone releases should not be used when you are going to be
painting or applying a patina acid. When I cast into alginate I
use LeKlair Cholesteral Plus Cream (found at the hair
section in Walgreens) as a release agent. It has the added
benefit of filling in pinhole and those ever-present air
bubbles. Gently rub the cream on to the mold in a swirling
motion using your fingertips to feel for imperfections. Do it
twice to be sure you have completely covered the alginate—even
the top edges of the mold should be covered.
The Formula.
Now to the mystery ingredients that make up FMG. There are five
of them. A liquid known as Forton VF-812; two powdered
ingredients, a dry melamine resin and a hardener; FGR-95 (known
as hydrocal); and chopped or woven mats of fiberglass.
Forton VF-812.
The liquid component, Forton VF-812 is a specially formulated
acrylic copolymer to cross link with the dry resin and hardener
to make the end product moisture resistant and ultra violet
stable.
Resin.
The dry melamine resin powder is added to insure moisture
resistance. One word of warning—the resin is extremely
hydroscopic. It will form hard lumps on exposure to atmospheric
humidity, so don't leave your container open too long.
Hardener.
The hardener is a chemical pH adjuster to insure that the
cross-linking with the acrylic copolymer and the dry resin takes
place.
Hydrocal.
The hydrocal is the basic ingredient. It is gypsum - available
from US Gypsum as FGR-95 or Densite HS from Georgia Pacific (see
supplier list at the end of the article) or their distributors.
Both gypsum cement products are formulated for hand lay-up but
also can be sprayed.
The first time I used FMG I
could not find a local supplier for FGR-95. Instead, reassured
by the folks at Johnson Atelier, I substituted Densite HL. (HL
designates hand lay-up there is an HS that means hand spray-up.)
According to Hiram Ball Densite can be used interchangeably with
FGR-95. I have found no perceivable differences between gypsum
products.
Fiberglass.
Fiberglass provides FMG with much of its strength. The table
below shows the proportions of chopped fiberglass to use.
However, there are disadvantages to using chopped fiberglass as
some of the strands may pierce the face coat and show on the
surface if the face coat has not sufficiently hardened. To avoid
this problem some lifecasters, including myself, use 6-10 inch
strips by 4 inches wide of biaxial fiberglass mat. Biaxial
fiberglass is a superior woven fiberglass that conforms much
more closely to the contours of a mold than does conventional
woven fiberglass which tends to bunch into folds, trapping
air-bubbles. The biaxial fiberglass will stretch-out much more
effectively, and will be about 30% stronger than an equivalent
weight of ordinary woven fiberglass. The fiberglass mat must be
thoroughly wetted on both sides then carefully smoothed on by
hand (using rubber gloves) to prevent air bubbles.
Preparing the Mold.
Thoroughly clean the mold using the original formula Amorall.
Mist the mold with the cleaner and blow it out. Use your air
compressor if you have one. FMG itself can also be used as a
rigid mold to cast FMG back into.
Application.
Three coats of FMG are applied to your mold. The first is a face
coat without fiberglass. I usually dilute the Forton VF-812
ingredient with 50% water to assure that it is thin enough to
capture the detail. This diluted mixture "white
water." (It had an absolutely benign meaning until the last
president gave it a double entandre.) After it has dried
to the touch a second coat is applied this time using a mixture
of chopped fiber glass or fiberglass strips. The strips should
be thoroughly wetted out before applying with the mixture. Once
the second coat has dried to the touch an identical mixture is
laid down as the final coat. Here I do a lot of smoothing using
my hands dipped in water to keep them wet. The end result is
that third coat has been smoothed out. If your piece is to be a
wall hanging then once the third coat is dried to the touch you
can attach a wire cable by securing it to in two places with
more FMG.
Mixing and Proportions. When
measuring, mixing or otherwise handling metal powders, dry
resin, powdered hardener, cabosil or any other powders
associated with the FMG mix, a high-quality (NIOSH-approved)
dust mask must be worn. All of those materials represent some
degree of toxicity if inhaled in powdered form. However, once
these powders have been dispersed into the liquid polymer
through mixing, the dust mask may be removed.
Forton
MG Mixes
|
Ingredient |
Plain
or
Pigmented |
Aggregates
Marble Dust |
Metallic
Powder |
| FGR-95 (Hydrocal) |
10 lbs
4.536 grams |
10 lbs
4.536 grams |
10 lbs
4.536 grams |
| VF-812 (water based Liquid
Polymer) |
5 lbs
2,268 grams |
6 lbs
2721.6 grams |
7 lbs
3175 grams |
| Dry Resin (Powder) |
1 lbs
453.6 grams |
1 lbs
453.6 grams |
1 lbs
453.6 grams |
| *Hardener (Powder) |
1/10 lbs
22 grams |
1/10 lbs
22 grams |
1/10 lbs
22 grams |
| Aggregate - Face coats |
N/A |
0-15 lbs |
N/A |
| Pigment Face Coats (Powder
or preferably Pre-Dispersed) |
1/10 lbs
22 grams |
1/10 lbs
22 grams |
1/10 lbs
22 grams |
| Metal Powders - Face Coats
(375+ Mesh) |
N/A |
N/A |
15 lbs
6804 grams |
| Chopped Fiberglass
- Back Up Coats |
see
below |
N/A |
N/A |
| Water |
N/A |
N/A |
2 lbs
907.2 grams
(optional) |
| Accelerator |
see below |
see below |
N/A |
| Set Time with no
accelerator |
60 min |
60 min |
60 min |
Chopped
Fiberglass added to
Forton MG by % Weight
|
Method |
% Fiberglass
Minimum |
%
Fiberglass
Maximum |
| Spray-up |
8% |
15% |
| Lamination |
6% |
10% |
| Pre-mix |
5% |
10% |
| Solid Casting |
0% |
0% |
The back-up coats (coats
following the face coat) require that the FMG be reinforced with
fiberglass. Though I mentioned I use biaxial fiberglass strips,
some lifecasters use chopped fiberglass strands for this
purpose. The Fiberglass Use Table provides the correct
proportions to use for the fiberglass strands in the mix. See
the Hand Laminated line.
The Gram Scale.
It is very important to assure accurate proportions when
preparing ingredients so that your cast cures correctly.
Therefore, a gram scale is a must-have to weigh-out the various
components that comprise the FMG casting system. A gram scale
can be obtained from most of the suppliers listed here.
Accelerator proportions.
A solution of one part aluminum sulfate and ten parts water (by
weight) may be added to the FMG as a drying accelerator. Using a
10 lbs. mix of FMG use only one to two tablespoons of the
accelerator. Temperature and humidity will affect the setting
rate. So you will need to experiment. With metal mixes the
accelerator is not needed for the face coat as it sets faster
than other mixes.
Hardener proportions.
Mark Prent of Pink House Studios has an excellent tip for
calculating the amount of hardener required for your mix.
Multiply 0.0485 times the weight in grams of dry resin. The
result equals the amount in grams of the hardener you will need
for your mix.
Mixing.
In a dry plastic bucket weigh the Forton VF-812 liquid polymer
in accordance with the table of FMG Mixes. I learned that when
mixing the face mix a small amount of pigment goes a long way.
It is difficult, however to determine the ending color until
after the piece has been demolded and dried. In the beginning I
had the tendency to over pigment the mix. In that case the
material will not cure within the 60 minutes and will not
achieve its full strength.
In the second dry plastic
bucket weigh out and combine the dry ingredients. Also if you
will be using a face coat of metal powders, aggregates or
fillers such as Cavasil (fumed silica) they should be added to
the same bucket. Blend the dry ingredients using dry blade with
high rpm drill to prevent clumping. You can make up a large
amount of dry blend ahead of time that should be stored in an
airtight container to prevent moisture from penetrating. If you
are careful it can last up to six months.
Always mix dry ingredients into
wet ones. So empty the dry mix into the bucket containing the
VF-812 polymer. Use a high rpm drill with a shear type mixer
such as the Stiffler. A high RPM drill and a shear-mixing blade
is mandatory to get a smooth well-dispersed mix. Typical mixing
time is 1 to 2 minutes. If you under mix metal powders you will
see the results of this mistake in your face coat of your
casting in the form of whitish swirls. This drove me crazy for
several castings until I finally figured out the problem.
Application.
Using rubber gloves, apply theFMG to your mold evenly about ¼
inch thick. Smoothing with your hands. Keeping your gloves wet
helps with this. If your mixture is mixed correctly you should
have a sufficient mixture thickness to allow you to apply to the
sides of the mold. If the FMG begins to slip down the sides of
your mold continue to gently pull it up with your hands as it
hardens and you should have adequate coverage.
Demolding.
When the casting has dried to the consistency of hard butter you
may use a knife to cut and even out the edges. Cut in the
direction of the mold -- never cut away from it as this can
damage your casting. If you are careful you can remove the cast
without damage.
Repairing damage.
If you do damage your casting during demolding (it happens to
all of us) or anytime thereafter, a fix is simple. Just mix up a
small batch of FMG, apply and let dry. After its dry you can use
wet sandpaper to smooth out the rough spots. Only you will know
there was a repair.
Cost.
Certainly FMG is more costly than casting with plaster as there
are more components. However, due to its ease of use and
significant timesaving the cost can be comparable taking these
factors into account. Most suppliers offer two choices, a
starter kit or a sculptor’s kit. The starter kit consists of
one gallon of VF-812 (7 lbs.), 10 lbs. of FGR 95, a 1 lbs.
package of dry resin and 22 grams of hardener. The sculptor’s
kit includes a five-gallon bucket VF-812 (40-lbs.total weight),
eight 1-lb. packages dry resin (8-lbs. total weight), eight
22-gram packages hardener (176-grams total weight). The sculptor’s
kit does not include the hydrocal component FGR-95. Fiberglass
has to be purchased separately, too. The cost for the starter
kits will average about $50, whereas the sculptor’s kit is
around $125.00. A 10-lbs. barrel of chopped fiberglass should
cost about $35.00 and 12-oz. weight of biaxial woven fiberglass
would cost approximately $14.00 per square yard. These prices do
not include shipping cost. Prices at suppliers will vary so
check around.
Coldcasting.
FMG is a wonderful medium to achieve simulated hot foundry
finishes. In my next article I will discuss cold casting
techniques.
Summary.
The are numerous advantages in utilizing the FORTON MG Casting
System. Among them are its ease of use, lightweight, safety,
outdoor use, flexibility and strength, and a material that can
take many finishes including cold casting. In conclusion, if you
have not used FMG, maybe now that I have given you enough
encouragement you will take the plunge. You will be surprised at
its ease of working. Once you have tried it, and mastered the
mixing proportions, I don’t think you’ll go back to casting
in other mediums for a long time.
Sources of Supply
The following companies will
provide the supplies you will need to prepare FMG. Most sell a
sculptor’s kit which includes a five-gallon bucket VF-812
(40-lbs.total weight); eight 1-lb. packages of dry resin (8-lbs.
total weight), and eight 22-gram packages of hardener (176-grams
total weight). It is usually most economical to get the gypsum
Hydrocal FGR-95 material from your local USG distributor as it
is extremely heavy and therefore costly to ship.
ArtMolds Sculpture Studio
18 Bank Street
Summit, NJ 07901
1-866-ARTMOLDS
For the location of a
distributor of FGR-95 near you, phone US Gypsum at (800)
621-9532.
For information on Densite,
contact a Georgia Pacific
Gypsum representative at 1-888-PLASTER.
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