You can improve surface finish by applying back pressure.

For Example:

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Without applying back pressure, surface finish reveals open foam cells.

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Drill holes into a board that can cover mold opening during casting.

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Apply Ease Release™2831 to board. Pour foam into mold and place board over mold with holes centered over cavity.

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Hold board firmly in place until foam stops rising. Let foam cure for 2 hours.

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Use a scraping tool to remove excess foam.

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Board is removed to reveal flat back of the casting.

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Pressure uniformly compressed foam into mold detail resulting in better surface finish.