There are 2 types of Polystyrene, expandable (white with foamy balls) and non-expandable (yellow). Both can be cut and sand down and are very soft materials therefore they will need to be protected with either:
· PVA and muslin, applied like paper maché or
· Artex or Idenden. These are pastes like poly filler, good to add texture if mixed with sand, paint or barque. If a thick layer is applied they can be as strong as rock and completely flame retardant. When half dry they can be sand down, carved or drilled into.
Polystyrene is easy to carve into and shape but it also reduces when exposed to heat. To glue polystyrene together it is best to use Expanding Foam. This will expand by a 1/3 and is a Polyurethane foam which can be cut and sand down but will not shrink with heat.
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