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Old 26th June 2020, 09:40
rossnzwpi rossnzwpi is offline
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If you are using polystyrene foam to form the basis of your shape and want to apply fibreglass over it then the main problem is that polyester resin aggressively eats the foam. It isn't about creating a smooth release layer - its about keeping any drop of the liquid off the foam. You better have some very waterproof sealant there. The resin could well attack the glue on parcel tape too so do some test pieces with whatever you try. I've used cling film over a form made of plasticine with polyester and believe me the polyester resin somehow got through the clingfilm and the plasticine stunk to high heaven of resin.

Another option is to use a more expensive resin - epoxy. It does not chemically dissolve the polystyrene foam. However it is still exothermic so don't let a great big pool of it form or the heat might damage the foam.
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