When casting Por-A-Kast into a urethane rubber mold,
always remember that you must use a good separator; if you do
not, the urethane resin will stick to the urethane rubber. A good
silicone release or wax release is absolutely necessary. Also,
keep in mind that resins of any kind are hard on urethane rubber
molds, and the molds will not last through many castings. If you
use a silicone rubber mold, no release is necessary (although
some people like to use one anyway.) Also, silicone rubber molds
will last through many more castings than will urethane rubber
molds.
You have about two minutes of working time withPor-A-Kast
. The material will become very hot as it cures; but unlike
polyester resin, no cracking will occur. You can add cabosil (a
glass-powder thickening agent) to Por-A-Kast to
patch or build-up on the surface of your cured casting; the material
will adhere to itself. To ensure the best possible bond, sand
the surface a little bit before patching. Keep in mind that you
don't have much working time.
Generally, Por-A-Kast may be de-molded in as little
as five or ten-minutes after casting into the mold. If, however,
you are pouring this material into molds that produce castings
as thin as 1/8-inch or 1/16-inch thick, you will have to wait
much longer for the castings to cure, since very little exothermic
(reactive) heat is generated in thin-sections of the material
to accelerate the curing process. In such circumstances, thin
sections may be removed from their molds after about twenty minutes,
but will probably still remain flexible for quite a while. You
may find this to be advantageous on occasion, as the partially
cured "flexible" castings will not snap or break, despite
their thinness, while being removed from the mold. They may then
be re-positioned before hardening-up completely. Thicker castings
of the material will not be flexible after about twenty minutes.
"Cold-Cast" Metal Effects with Por-A-Kast
Metallic powders may be added
to Por-A-Kast in order to achieve a very convincing
"cold-cast" metal look. The mix ratio should be approximately
two units of metal powder by weight to one unit of Por-A-Kast
by weight (figuring the combined weight of the two components
into the single unit-weight of the Por-A-Kast.)
Because you will have very little working time; if you are adding
metal powders, it is a good idea to divide the metal powder required
into two equal amounts, add half the powder to one component and
the other half to the other component; then mix each thoroughly
to prevent "settling" of the metal particles. Finally,
combine the two components together, with the metal powder already
suspended in each component. After de-molding the "cold-cast"
metal casting, rub it down with 0000 steel wool, and then hand-polish
with any good metal polish.
Por-A-Kast - 2-Gallon kit...................................................
$105.00