Little is more frustrating than trying to use the telephone to
figure out why a customer is having trouble with a product. I hear “I
read the instructions”, “I weighed it carefully”, “I cleaned it
thoroughly”, and so on.
Please do not misunderstand, it does not happen all that often to
begin with, but I do hear some really odd-ball goofs.
Read the instructions thoroughly. Silicone RTV is an engineering
material with specific properties that are designed for your
application. It is not Campbell’s soup.
Do not dip the model in light machine oil before making the mold.
(Do not create your own release agent). Release is not needed for
most materials, including carved waxes and RP resins.
Do not use silicone spray on glass frames. Use TFE spray. Call me if
you can’t find any.
Do not try to de-air in a tall narrow vessel, use the largest
diameter, shallow bowl you can fit under the bell jar. This exposes
more surface area to the vacuum and reduces rise and speeds de-air.
Do not use a postal scale, baby scale, fish scale, bathroom scale.
Yes, I have heard each of those. Use a scale capable of reading to
1/10 gram. You will never have a problem, other than maybe
arithmetic. There is not a lot of tolerance in 10 to 1 ratio, unless
you intend to change the properties of the mold. Call me about that.
I may have an alternate catalyst for you.
Resist placing your uncured mold in a freezer over-night to de-air.
It works, but moisture can cause problems from time to time.
Resist trying to fast cure in a kitchen oven or toaster oven.
Controlled 120F cures our silicones in one hour.
Make sure your vacuum pump has been maintained properly and is
pulling sufficient vacuum.
Test spot a material you are thinking of using as a model. When you
make a normal mold, drip a little of the leftover on the material you
plan or hope to use as a model. If the little drip cures, go for it.
I am not being insensitive. The “little drip” is the droplet of RTV,
not the craftsman.
Realize that if the mold you made last year has become gummy, it is
not silicone. Some companies do not make it very clear that they are
selling polyurethane RTV.
Making a silicone mold is very simple if you do not try to discover
new ways to do it. Our instructions are based on 17 years of
experience with silicone RTV and may not always be interchangeable
with another brand.
If I have left anything out, please chime in with more suggestions.
If you know of any other craziness, please let’s hear it. Together we
may be able to set aside some of the HOOKIE-BOO.
Please call me with questions.
Zero-D Products, Inc.