I received the following inquiry on using ceramics with art / epoxy resins and thought I would provide some answers here as it appears to be a common problem for many artists.
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Hi Jean,

I hope you can help me!
I have been using Liquid Gloss (epoxy resin) for over 8 months now to coat paintings that I do on bisque fired clay. I fire thin clay tiles, prime them with a gesso primer and paint them with gouache. The resin has not been a problem to work with and sets nicely as a surface finish (even on slightly uneven surfaces)…I have not had problems with bubbles or peeling but just this week since the weather has cooled I have found 6 pieces (out of 100 or so that have split). The resin has not lifted off the surface but rather lifted and taken a good slice of the clay with it…I thought at first it may be a weakness in the individual clay pieces or even movement in the clay (drying out with less humidity) but now I’m not so sure.

Does epoxy resin expand or contract once it is fully set? If so, is it to do with dry/moisture heat/cold…I have put test pieces in the fridge, in the sun and rain and still not been able to make them crack. This is happening to pieces that are more than 6 months old…I would be grateful for any suggestions or solutions? I would be happy to try another material or product?

Thank you!
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So what can we do to prevent de-lamination issues such s the one faced by our ceramic artist?

Here was my answer to the query:

Expoxy has a much higher linear thermal expansion index than ceramics -about 8X more. This is true even if conditions are very dry, it really has mostly to do with the temperature variations. Since you are seeing the separation (actually called de-lamination) on 6 month old pieces, we can eliminate humidity in the ceramic as a factor, and assume that your ceramics are dry and therefore very stable. The top resin layer, being quite thick, has 8X more expansion and contraction than your ceramic with differences in temperature and will end up separating from the ceramic base, taking with it a top layer of ceramic (because the bond between the ceramic layers is weakest).

The other problem you are seeing is that epoxy resin, when applied and then curing, has significant expansion and contraction as well, because its temperature changes. So effectively, the separation probably starts from the very beginning.

Your options are probably to:

  • Do smaller pieces with a smaller footprint – surface area. Because it is a thermal expansion problem, it will happen to the larger pieces (the ones with the largest surface area), and to the ones where the resin layer is thickest.¬†
     
  • Use a much thinner layer of resin on top of the pieces -try brushing it in
  • Use plasticized ceramics. You can add plasticizer to ceramics to allow them to expand and contract at a closer rate to Epoxy.
  • Use plaster.¬†Plaster expands / contracts much more than ceramics (3X more), but 3X less than epoxy. So using plaster will work better, but larger pieces will still be at risk.
  • Use a filler with the ceramic that does not expanding with increases in temperature -that is why people use fiber glass for instance to prevent those type of variations. I would research epoxy fillers / additives to prevent thermal expansion to see if there is anything better than fiberglass, which is partially opaque.

Good luck!