Subject: Silicon ?

From: "Randy R. Cox" <[email-masked]>
Date: Sun, 15 Dec 1996 10:29:24 -0600

For years I've used clear, cheap, silicon right out of a caulking tube
for many purposes--almost as useful as duct tape.  Several years ago,
they began to "impove" the product making it paintable in some cases,
adding years of guarante and additional price in others.  The old stuff
gave off acetic acid and smelled like vinegar.  The newer stuff smelled
like ammonia.  As the years go by, the old stuff gets harder to find and
more expensive where it used to be cheapest of all.

The new "improved" silicon rubber seemes to have an adverse reaction to
uncoated plastine clay causing it to desolve and get mucky.  Does
anybody out there have an understanding of this product, and if so, how
can I tell by reading the label which is the old stuff and which is the
new.  Right now, the only clue I have is the "improved" designation.  As
the years go by, this will probably be dropped.  I'm very dependant on
this stuff, and the alternative for me requires triple beam scales and
critical mixing and time constraints.

Thanks in advance,
You guys are great!,

Randy

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From: Jay Hayes <[email-masked]>
Date: Sun, 15 Dec 1996 18:33:25 -0800

> critical mixing and time constraints.

I don't know that the lable will tell you the real difference between
the two types of "calking". I suspect one type is an acrilic latex
modified with silicon and the other is mostly silicon.

If you contact Dow Corning's Technical Sales department (or GE's) they
can give you the first hand info you need.

I have used a lot of different silicon products for molds and other
applications. Most of the single component silicons like your calking
and sealers/adheasives are moisture cure materials. The moisture that is
ever present in the air acts as a catalyst to triger the cure reaction.

Two component silicons on the other hand use a platnium based catalyst
or other chemical to initiate the cure reaction.

The problem you are having with "plastine clay" is a reaction to the
sulphur in the clay inhibiting the cure of the silicon. If you give the
clay a couple coats of clear acrilic followed by a couple coats of
Johnsons paste wax or other compatible mold reliese, your problem should
be eliminated. You can also use a different type of clay that does not
contain sulphur.

Try a little test batch to start.

Hope that helps,

Jay