Making Molds

Making Molds

Post by Michael S. Nuckol » Mon, 24 Nov 1997 04:00:00



    Just thought I would pass along information about an experiment I did
this past week to see if I could make a good, reusable mold...

    Recently, I posted a question for the group on how to make molds into
odd shapes...  I received good suggestions from the group which I
appreciate.  I took these into account and decided to try and make a mold.
In experimenting, I was able to come up with yet another way to make molds
using a large bowl or other concavity as an intial form.
    I went to my local home depot and bought a can of expanding foam used
for sealing cracks and crevices in your home.    This stuff is designed to
be sprayed in wall cavities or other holes where it expands and then hardens
in about a day.  I have used this stuff before and knew it was very sticky.
Once you get it on your skin (or anything else for that matter), it stays
there until it dries hard (unless you douse your hands in toluene -- which
is not a very good idea from a safety perspective).  When this stuff dries,
you must scrape it off to remove it.  Bottom line -- wear gloves and put
plenty of newspaper down.  Plan on tossing any tools that you use that
cannot be scraped.
    Anyway, I coated a very large punch bowl with Saran wrap.  Then, I
coated the inside of this with the expanding foam.  I used a wooden stick to
push it around, again wearing gloves to avoid getting it on me.  Then, I
added a layer of styrofoam peanuts that were used as a packing material by a
mailorder glass retailer (great way to recycle...).  I sprayed some more
foam to hold it together.  I repeated this again and again, layering the
stuff like lasagana, until I had filled the form up.
    Well, I thought I was pretty smart at this point.  I followed the
instructions on the container of the foam and let it sit for a day.   I went
to pull it out of the form and found that it was still soft.   Completely
disappointed, I left it to sit longer, planning on tossing it.  The next
week, I was cleaning house and went to throw the concoction out and
discovered that it had finally hardened.  Evidently, the Saran wrap had not
allowed the foam to completely de-gas and harden.
    E***d, I removed it from the form.  I found that the surface was still
not completely smooth, and had many bumps in it -- I should have used more
foam for the initial layer.  In recollection, about an inch would be best.
This will require several cans of the expanding foam to get it this thick.
Anyway,  wanting to salvage it, I removed all loose styrofoam and Saran wrap
from the mold.  At this point, I probably could have still used it though I
would have to have been very careful cutting and piecing my glass.
Nonetheless, I still wanted it to be smoother.   Taking another suggestion
from someone on this newsgroup, I coated the whole thing with a very thin
layer of papier mache.  This made a smoother surface.
    I am now using the mold and it is working great!  Pins go into the
surface very easily and the pieces are staying nicely in place.  I have not
begun soldering yet and will report how this works out when I get that far
(which may be a month from now!).  I will also report if the mold is in any
condition to be reused after I am done.