Sealing foam - not sign making

[Mark Bolton]

Not a sign making application but thought this may be the best place to get good answers. We are having to CNC some sink/drainboard mold plugs for a concrete counter top. Was planning to CNC the 3D plugs out of 2" XPS. Once they are machined they will have to be sealed (spray) to help with the release (they will get spray release as well when they are cast). Does anyone have any experience with a good product to spray/seal XPS or ISO?

Thanks for any input.

[Adam Herman]

i think i would fiberglass them or paint them with epoxy? nothing you can spray from a can will fill the porosity in the foam. a sanding primer for automotive applications may work as well. You will want to make the mold as smooth and perfect as possible to keep you from having to do more work on the part. our plugs were made of cnc cut basswood or similar and coated with a plaster like mix before final sanding and shaping. and our molds were made with high strength fiberglass and special resin around a steel frame. everything was polished and waxed. also be sure your sink plug has a draft angle so it can be removed.
I worked for a composites manufacturing company (wind turbines, hoods for Caterpillar machines and mass transit interior panels)

[Mark Bolton]

Thanks Adam. We've got the draft in there. These are one shot plugs so we didnt want to go to the grief of hard cast or molded plugs. Filling porosity is what I was concerned with. I had thought about vacuum forming some sheet film over top with some spray adhesive but didnt want to reinvent the wheel.