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Polishing Shrinkage Wrinkles in Polyester Clear Castings



These imperfections are normal in casting EP4101, and are a result of shrinkage upon curing. The wrinkled surface can be finished by buffing and polishing.

First, post-cure the casting at 130 F overnight. This is necessary because the surface of the casting is fairly soft and a post-cure will increase its hardness.

Next, use a coarse (the rating depends upon the height of the wrinkles) sandpaper to remove the wrinkle lines. 120 grit is probably the lowest you would want to start. Wash the piece in water to remove all loose particles.

Continue to use finer and finer sandpaper, being sure to wash the piece thoroughly in between stages. A shiny, polished surface should achieved by going up to 600 or 1000 grit paper.

For best results, use Eager Plastics' buffing compound.



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