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2 | 2 -- THE SURPRISING BENEFITS OF THE FORTON MG CASTING SYSTEM
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 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.
Douglas and Sturgess
730 Bryant St.
San Francisco, CA 94107
1-888-ART-STUF
Pink House Studios
Atten: Mark Prent
35 Bank St., St. Albans, VT 05478
802-524-7191
Specializing in life-casting supplies
Johnson Atelier
60 Ward Avenue Extension
Mercerville, NJ 08619
Phone: (609) 890-7777
Fax: (609) 890-1816
Be sure to ask for their extensive catalog of sculpture supplies
Ball Consulting
Atten: Hiram Ball
Suite 201
338 14th Street
Ambridge, PA 15003
800.225.2673
724.266.1502
724.266.1504 Fax
For the location of a distributor of FGR-95 near you, phone
USGypsum at (800) 621-9532.
For information on Densite, contact a Georgia Pacific
Gypsum representative at 1-888-PLASTER.
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