Flow Increaser works as a high rise
agent. To make high volume batches, we do not use High Rise
Foaming Agent with the new High Grade Latex. Rather, we add
2 to 4 grams Flow Increaser (per 150 gms High Grade Latex
Base) to the bowl prior to whipping. This causes a greater
frothing action, and the foam rises higher, and more quickly.
For still higher batches, we also increase the Foaming Agent
to as much as 35 gms per 150 gms High Grade Base. IMPORTANT
NOTE: This increased frothing lets you turn down the speed
of the mixer at an earlier time than the standard run. Care
must be taken to not retard the gel by pouring the Gelling
Agent when there is still too much ammonia in the mix. Also,
when using more than 30 gms Foaming Agent, there is a retarding
effect on the gelation, see #2 below.
mechanism works as follows: All of the latex in the bowl
is covered with a thin layer of Foaming Agent (soap) at all
times. This coating persists throughout all of the whipping
and refining stages. Every cell is coated with this thin
soapy layer. At the time the Gelling Agent is poured, there
is no exposed latex. The first job of the Gelling Agent is
to break down the soapy layer. When the soap has been broken
down sufficiently, gelation begins. It stands to reason that
if there is a thicker layer of soap on the cells, the gel
time will be longer. So in very hot conditions where more
working time is needed, we prefer not to cut the amount of
Gelling Agent too low. Rather, we add extra Foaming Agent
(up to 35 gms per 150 gms High Grade Latex Base) for protection
against gelling, and we pour the Gelling Agent sooner that
the standard instructions. This gives a much better result
than cutting the Gelling Agent down to less than 10 or 11
gms per 150 gms High Grade Base. In cold conditions, one
may feel free to add more Gelling Agent to speed the gelation--up
to 20 gms per 150 gms High Grade Latex Base, as well as adding
time to the refining stage.
is added to the bowl mixture, not to the Gelling Agent.
It would be nice to use the colorants as tracers in the
Gelling Agent, but unfortunately our pigments and our Gelling
Agent do not mix. The product of mixing the two is a thick
gelatinous mass, which will not disperse properly. We add
our pigments to the bowl mixture before or during whipping.
When it is eventually time to pour the Gelling Agent, the
observant user can see that the Gelling Agent causes a
lighter color in the foam. We know this is not as effective
as a color tracer in the Gelling Agent, but the conscientious
user should be thorough with the gel mixing, irrespective
of color. If we ever discover a way to make the pigments
miscible with the Gelling Agent, we will make an announcement.
can be made very dense and tough, if desired. This is accomplished
by whipping to a lower volume. When doing this, one will
need to add some time to the refining stage so as to compensate
for less ammonia loss during the short whip cycle.
rise foam shrinks less than low rise foam. All foam is
a combination of foam ingredients and air. The foam ingredients
include solids and water. In high rise foam, there is a
greater proportion of air, and a lesser proportion of foam
ingredients. This also means that there is a lesser proportion
of water. The loss of water is what causes shrinkage, so
less water loss will cause less shrinkage. In low rise
foams, there is a lower proportion of air, and a greater
proportion of foam ingredients (and greater proportion
of water). This causes more shrinkage.
found that higher rise batches can be almost free from shrinkage.
Firstly, the foam itself shrinks very little. Secondly,
in the application, the foam is so soft and supple,
it stretches without exerting much force. The very act
of applying the piece usually stretches the foam sufficiently
to behave as if there were 0% shrinkage.
factor in the shrinkage of foam is the mold material.
A porous mold will cause foam to shrink less than a non-porous
mold. Porous molds absorb part of the water in the foam,
allowing there to be less water available for shrinkage.
Non-porous molds will not absorb any of the water. We
also feel that non-porous molds may cause a greater smelliness
in the foam for the same absorbency reasons. This of course
goes away when the pieces are washed.
We prefer to use a foam injector, even
when open-filling molds. This protects the foam from contact
with the air, so it doesn’t skin over while you are
working with it.
Molds are lined up with all the positives and negatives
placed in the same configuration. Since we are right handed,
we use the negative on the left with the positive on the
right--opened like a book. When the negative has been filled,
the positive is closed bookwise onto the negative, slowly
lowered to let excess foam bleed out, then when contact is
made, pressed firmly for five seconds, or strapped.
To fill, we shoot a thick swath of foam across the top edge
of the negative sculpted area. We then pick up the negative's
and tilt it, so the foam flows down the entire sculpted area.
It may take a couple of firm shakes to make the foam cover
the entire area. As the foam flows downward, it tends to
make a thin coating, and any air bubbles in the mix will
become visible. They are popped with a wooden stick before
the positives are closed onto the foam. Remember to let the
positives gently settle onto the negatives. Excess foam must
be allowed to vent. This creates less internal pressure,
and allows less resistance between positive and negative,
making thinner edges.
2. Injection, Unstrapped
If a two-piece mold is to be injected, it is convenient
to fill by injection, and let the mold halves separate from
the filling pressure. This allows flow over the surfaces
and tends to flush out stray air bubbles. Once excess foam
is seen venting out the edges of the mold, the injector is
removed, and the two mold halves are pressed together or
strapped. When filling this way, have the negative piece
on the bottom, with its sculpted interior facing upwards.
3. Injection, Strapped
Multi-piece molds usually need to be
assembled prior to filling. Try to have the injection port
open at a thick part of the sculpture. Have the attitude
of the mold adjusted so the foam enters at the bottom of
the cavity, and exits at the top. This only applies to
the attitude of the fill--not necessarily having the sculpture
right-side-up. We usually have air vent holes of 1/8” diameter
drilled into the positive near the perimeter of the sculpture,
staying well clear of the cutting edges, and turn the mold
so that these holes will be at the top, when filling. Foam
should enter the bottom of the cavity, and move upwards,
expelling air at the top as it goes.
1. The cure “window” is larger
at lower temperatures. At 185° F, foam may take 3-hours
to cure, but at 4-hours, it could be overcured. This overcured
foam loses tear strength, and in extreme cases, becomes crumbly.
The same foam, cured at 165° F, may take 5-hours to
cure, but even if cured for 7-hours, would still be fine.
In other words, a low temperature cure could have a three
hour window, where the cured foam would be usable. A 200°F
cure may only have a 20-minute window where the foam is usable.
2. Steam lakes are areas of foam that have been pushed away
from the mold surface by pockets of steam, then cured into
that incorrect shape. These areas have all the detail of
the sculpture, but they are depressed and too dense. This
is a hazard in non-porous molds, such as epoxical and fiberglass.
It is a problem that can be remedied.
The first step is mold preparation. Non-porous
surfaces are to be coated with a thin solution of paste
wax (such as Johnson’s wax for floors) that has been cut with
99% alcohol. This resulting “alcowax” should
be very thin and “watery.” Paint it into the
inside of the mold, do not allow to pool, and when dry, brush
it out with a dry brush. The mold surface will become polished
and shiny. More importantly, the mold surface will be sealed
from outgassing, which we feel causes sites for steam laking
Secondly, cure at a lower temperature
(for a longer time). We often use 165° F for 5-7 hours
for this kind of mold.
Despite these efforts, some molds (usually
fiberglass) continue to be difficult. A final solution
is to cure a skin of foam into the open mold, prior to
filling completely. First, mix a small batch of foam that
will be roughly enough to cover the inside of the negative.
When it is ready, brush this foam into the negative, keeping
the foam about 1/8-1/4” thick
everywhere. Stay away from the edges. After the foam gels,
put the mold pieces into the oven OPEN, and cure at a very
low temperature. We have had to go as low as 125° F for
10-hours. Next, cool the mold, and fill with foam in the
usual way, whether by closing and shooting, or by open pouring
then closing. Cure this larger batch also at a low temperature--around
165° F--so that it won’t overcure the skin that
is already inside. If the skin is a little undercured, that
is acceptable. The volatile Curing Agent will make plenty
of fumes that will permeate the skin and cure it.
Do not worry about the interface of the two layers of foam--the
bond will be intimate. Do be careful to have a smooth interior
that is free from areas which catch air bubbles when the
bulk of the foam is filled.
This method takes a lot of extra time, but it is worth it,
when no other method will give satisfactory results.
3. Sometimes it is useful to have a rubber
skin prepainted into the mold. This gives extra strength
to areas of chafing, like the soles of feet. High Grade
Foam Latex Base is simply painted into the mold where needed,
and allowed to dry before filling with foam. No Curing
Agent needs to be added to the Base; volatile Curing Agent
fumes will cure this skin along with the foam.
© GM Foam, Inc. 2009