resin, fire resistante

Fire retardants are generally brominated aromatic compounds or phosphate salts. Polymer-bound bromides are preferable to polybrominated biphenyls because they do not migrate into the environment. Polybrominated biphenyls have a low vapor pressure and migrate through the air into the environment, and have been found in women's breast milk, causing concerns. There are emulsion polymers that contain dibromostyrene which can be applied to fibers or finished materials as a coating. Certain aromatic phosphorous compounds or oligomeric bromides may be possibly added to your resins.

What are you wanting to paint and how hot is it going to get and for how long?

You cannot tart up a resin to make it fire proof - forget it. Go out and buy some.

Fire retardant paints will not sustain combustion. The classical chemicals for this are antimony oxide and a chlorinated resin. These have been taken off the market in most parts due to concerns over antimony use.

Intumescent paints blow up into sponges when heated (a la Apollo) - also very specialised.

Otherwise if heat resistance is the requirement then paint a small sample patch and treat as it might be exposed in service. - Good luck!!! If it works OK if not try again.

If you can fill the polyester then you can use ATH (Aluminum Trihydrate). This material has been used for many years as a flame retardent. The action is liberation of H2O at ~ 215'C, this will reduce the capability of the material to substain combustion. It is cheep, and a non haz mat material.