Why
Bubbles?
Stick a rock into warm water and let the water cool and you will see how
bubbles can form. Hot water holds more air because there is more space within
the water molecules. But when it cools, the air has to go somewhere as the
water molecules come closer together, so it creates bubbles that come out of
solution and adhere to the surfaces within the cup.
But
the bubbles can easily be removed by reducing the surface tension on the parts.
A touch of Bubble Buster and the bubbles will rise to the surface and off the
rock. This is how bubbles can form with ComposiMold and PowerMold and also how
you can remove bubbles from your mold. Here is a breakdown of different
methods:
Bubble
Buster:
The first approach we discuss is the use of Bubble Buster. Bubble Buster is a
PVA/water solution that reduces the ability for the bubbles to adhere to the
surface of the master. To use, just spray, dip, or coat the Bubble Buster over
the part you are molding. Be sure to get lots of the PVA/water solution in the
cracks and corners. You don't have to let the Bubble Buster dry before pouring
on the PowerMold or ComposiMold. If needed, use a mold release (vegetable oil,
Vaseline, or mineral oil will be fine for most molds) before putting on the
Bubble Buster.
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| Bubble Buster sprayed on to your master before making your mold |
Sealing: The Bubble Buster
will reduce most bubbles from adhering to your master and thus give better
molds, but if you are still getting bubble in y our mold, then there are many
other potential solutions.
Is your original part sealed? Air that is in the
plaster can come out and into the ComposiMold. This is probably the cause if you are using plaster, clay, or wood as the
master. To solve, seal the master first with several layers of polyurethane
spray, shellac, or other wood sealers. Elmers-like glue (PVA glue) works well
to seal parts.
Pulling Out the
Bubbles:
Are the bubbles getting stuck in cracks or undercuts?For any undercuts, you will likely have to pull the bubbles out so
they can float to the surface instead of get stuck under the ledges
(undercuts). Use a toothpick or small screw driver to pull the bubbles away
with a toothpick. Even better: soak the toothpick with Bubble Buster and then
pull away the bubbles.PowerMold is thicker than ComposiMold, so pulling away
the bubbles will be more difficult with PowerMold, but the same approach works.
If at any point, the PowerMold is too thick, take a hot air gun and warm it up
more, but be careful not to overheat above 200 F.
Mold Release: You may also have too much mold release, so
the interaction causes bubbles. This seems to happen quite a bit when you use a
vegetable oil as a mold release or don’t let your silicone mold release dry
first, but other mold releases may have this affect. Be sure to wipe off any
access mold release. You can use Bubble Buster over your mold release without
any harm.
You may have bubbles in the ComposiMold from
bubbling in the microwave. It may be worthwhile to remelt the ComposiMold and
let it cool at room temperature so the bubbles can rise to the top and escape.
Pouring: You may be putting bubbles in when you pour
the ComposiMold into the container. The best way to avoid this is to just pour
gently into the lowest area of the mold so the ComposiMold rises up over the
part. Be sure any holes are filled with the ComposiMold and you are not
trapping air. You can also use a toothpick to pull bubbles out as you are
filling your mold box.
Heating: You can also adjust
the heating: Heat up your original slightly with a hot air gun and let the
ComposiMold
cool before pouring it on your part. The ComposiMold will be thicker when you
pour, but it will still fill most gaps. The heating and cooling reduces the
temperature difference between the ComposiMold and master and reduce bubbles
from forming.
If
you are still having bubbles (and your master is sealed well) another approach
is to brush on the ComposiMold or PowerMold and then if necessary heat the
PowerMold while on your mold with a hot air gun to break up any bubbles with
the hot air gun. Be careful with this approach that you don’t overheat your
master or the PowerMold. Heat jJust enough to keep it warm and break up the
bubbles. When you pour the rest of the ComposiMold over your master, it will
re-melt this layer, but that won’t matter as the bubbles will already be out of
the layer against the master.
We
do also get asked about degassing with a vacuum and this approach does not seem
to work very well. It will make a mess as the ComposiMold expands. We think
because the vacuum reduces the boiling point and makes the ComposiMold boil.
The
great advantage of PowerMold and ComposiMold is that it can be reused and
re-melted. So any mistakes or bubbles that you don’t get out can be fixed by
heating that area or remelting and making the mold over again. Let us know what
other methods you find that work for you and keep experimenting!
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