When making urethane or styrene foam models either by hand or on a CNC mill, you will find that these models can be fragile in their thin sections, dusty, and not able to be painted. Sealing the model helps make it stronger as well as able to take paint. One method that has been tried is to use spackle or artist's gesso to seal the foam. The drawback to this method is that the gesso and spackle are heavy and can take a very long time to dry. A better solution is to use UV-curable surfboard polyester resin. These are low viscosity and easy to use and brush on the part. Putting the parts out in the sun for about an hour cures the resin. The result is a stronger, cleaner part. UV cure polyester is available from surfboard materials shops, or from Fiberglass Supply (Bingen, WA, www.fiberglasssupply.com).
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