Plastic Bags and Epoxy

When working with epoxy it is good to have something under the thing being epoxied to separate the thing from the table upon which it is sitting. This keeps the table clean from drips and keeps the thing being epoxied from being glued to the table.

I often use something cheap and readily available such as waxed paper. The downside to waxed paper is that it can leave a waxy residue on the surface of the epoxied part, and it sometimes doesn't release properly. Instead, it tears and leaves pieces embedded in the epoxy.

People often use polyethylene plastic sheets or bags instead. It is pretty cheap, and generally available from builder supply and hardware stores. It comes off epoxied surfaces fairly easily. However, it is optically translucent and difficult to see through. Thinner sheets also have a tendency to wrinkle, and those wrinkles transfer into the resin. The resulting surface, even if you smooth out the wrinkles, is dull in appearance.

As I happened to have two kinds of polyethylene available, one from the bag my morning newspaper is delivered in and the other which was used to secure the bottle of resin as it was shipped to me, I decided to see how well they worked for bagging wet resin surfaces.

I also happened to have a large roll of shrink wrap plastic, so I tried that as well. Shrink wrap plastic is optically clear and about as flexible as the newspaper poly bag. The resin bag was a bit less flexible, but intermediate in terms of optical clarity.

The results were amazing: While both poly bags did pretty much what I expected, i.e., dull finish with wrinkles, easy to remove with a bit of tugging, the shrink wrap plastic delivered a superb glossy finish with very few wrinkles. The plastic practically fell off the resin with no effort. Wow!

Even the area where the steel block was used to press against the bag against a test piece of epoxy soaked glass was flatter and shinier than where the poly bag was.

I'm going to see if the shrink properties can stand in as a replacement for vacuum bagging, too. It almost certainly won't be quite as "tight" as vacuum bagging, but it might be adequate.