What to use to make a mold?

On Mar 23, 8:28*am, wrote:
On Mar 22, 5:23*pm, AK wrote:

I want to make a small mold I would later use to create a fiberglass
container to hold lead weight. It would be nice if *mold material can
withstand 500 degrees Fahrenheit so I can pour lead into it and then
cover it by fiberglass. Alternatively I would use the mold to create a
fiberglass container first and fill it up with lead pellets. So my
question is what do I use to make a mold, gypsum if so what kind,
anything else?

Andrzej

sand

http://en.wikipedia.org/wiki/Sand_casting not quite that simple in
practice and would also req the purchasing of some specific setup
materials which are not found at Home Depot etc...

You should go the wood or plaster route.Wood is dead simple if your
shape is not to complex. I saw that Steve quite rightly mention of
worry of plaster and residual water/steam being an issue... hence
the very specific directions I layed out for preheating/drying your
plaster mold BEFORE lead is poured in. If it survives the 4 hr
incremental ramp up to 400deg, it will not break from the pour since
all the water will have been evacuated by then. If in doubt, leave it
in the oven for an extra hr or 2 at 400ish...

I dabble in investment casting, and the same methodology applies for
pouring 1700-2100 deg metal (bronze, slver, gold, etc) into a plaster
mold, except the heatup/dryout process brings it up to 1000deg over a
5, 7, or 12 hour ramp up (usually spending some an hr or 2 at 1300deg
to vaporize out the wax remnants before ramping back down to
1000ish).

-Paul