8. Additional information
Using polyester resin
Polyester is the plastic substance used in fibreglass work for building boats, car
body parts, etc. Various things are added to it to make it work better for various
jobs. Talk to your supplier and explain what the resin is to be used for. Your
supplier should be able to help you.
Hardeners
There are two systems used to harden polyester resin, and each system uses two
chemicals. For resin casting and most fibreglass work we use peroxide and cobalt.
('Body filler pastes' use the other system.)
Cobalt is a purple fluid. Ask the supplier to mix the right amount of cobalt into the
resin. After it is mixed, the resin must be stored in the dark, or it will harden.
Peroxide is a hazardous chemical. Avoid contact with skin. Store in a PVC
container, in the dark, below 25 degrees C. Never mix it with cobalt (except for the
cobalt already in the resin), or it will explode. Mix very small quantities (about 1-
2%) of peroxide with resin or it will overheat.
Wax-free 'Air inhibited' resin 'B'
This type of resin is used for 'gel-coats' on boat moulds, where the resin is going to
be built up in stages. We do not recommend using this resin for the PMG. Any
exposed surface will remain tacky indefinitely. Ask for resin 'A', or better still
'casting resin'.
Thixotropic additive
A special powder of very light silica is often added to resin to make it thicker, so
that it is easier to spread it with a paint brush. This powder is not needed for
casting resin . If it is already added, it does no harm.
Styrene monomer
Approximately 35% of the resin as supplied is styrene monomer. This is used for
thinning the resin. It causes the smell. It is possible to add a little more styrene
monomer (10%) to make it more liquid.
Pigment
Pigment is used to colour the casting, if a coloured finish is desired. Add pigment to
the first mix, which will be on the outside of the casting. Add no more than 10%
pigment to the mix. It is not necessary to add pigment to the resin. Without
pigment, the casting is transparent and the coils are visible.
PMG manual
page 49
June 2001