Polyester Resin Curing Trouble

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This topic contains 7 replies, has 2 voices, and was last updated by  Kayla Burke 1 year, 8 months ago.

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  • #8294 Reply

    Kayla Burke

    I have been working with polyester resin for 3 years now and lately I have been having problems getting my objects to cure properly. I am pouring 4″ deep molds. The castings are coming out so beautifully, crystal clear and I have assumed they are cured properly… Not showing fingerprints when I touch them and they don’t seem sticky. However, I have been wrapping the resin items in tissue paper to ship them and even though I swear they are cured, the paper has been sticking to the surface and causing me many nightmares. This is even happening to castings that I have been handling for months now, showing no signs of fingerprints. I am really confused and frustrated.
    I know there is the resin spray sealer, would that solve this problem?
    I would like to find a different solution to the spray, if that is the answer. I need a product with more control. My casting are fairly big 4″ tall by 2″ wide and odd shaped. I feel the spray would be hard use causing dripping, splatters, etc.
    The castings are coming out of the molds so perfect and glassy, I hate to ruin them by adding spray spots, lines and drips.
    What about leaving them in a room with a dehumidifier and the heat cranked up?
    Any product suggestions or tricks would be much appreciated!

  • #8300 Reply

    Katherine Swift

    Hi Kayla,

    What your are describing is typical of polyester casting resin. The surface exposed to air during curing will remain tacky. Yes, everything is cured underneath, but it’s like putting your finger onto tape. I have pieces cast from YEARS ago that are still sticky.

    The gloss sealer spray would work to take care of the tackiness, but I understand your concern with drips. Your other option is to sand off the back of the pieces, although with the size of your castings, that’s a lot of work. A third possible option to try is to apply a doming resin to the surface, but that may not give you a nice flat back.

    I wish I had an easy solution for you.

  • #8304 Reply

    Kayla Burke

    Hi Katherine,
    Thanks for the response. My entire object is tacky, even areas that were not exposed to air during the cure time. (maybe I am taking them out of the mold to soon)
    Is there another crystal clear resin you would recommend for this kind of deep casting? I would love to get away from the polyester resin but the crystal clear results keep me using it. Is there any kind of brush on sealer to use? Also, what is doming resin?


  • #8333 Reply

    Katherine Swift

    Hmm. Since you have other sticky spots, maybe your resin wasn’t mixed well enough. I don’t usually see that problem with polyester casting resin unless we are talking the surface.

    The Resin Obsession super clear resin will work well for your purpose. https://shop.resinobsession.com/collections/resin/products/resin-obsession-super-clear-resin-12-oz-kit It pours very clear and doesn’t have the horrible smell polyester resin has. You are going to have to pour smaller batches, however. (Three ounces is the most we recommend mixing at once.) If you pour the next layer when the previous layer has started to gel (as opposed to fully cure) demarcation lines shouldn’t be a problem.

    I don’t have a good brush on sealer to recommend. I used a few in this video on our youtube channel, but wasn’t crazy with the results. https://www.youtube.com/watch?v=Wm89lAqDCqo&t=3s

    By doming resin, I mean a resin that when mixed, has enough surface tension to stay on a flat surface. In other words, it doesn’t needs sides to stay in place. Polyester resins are not doming resins. (Neither is the super clear resin.) It tends to dome and may be slightly higher in the center than on the edge.

    • #10530 Reply


      Thanks Katherine.
      Its reassuring to receive your response.
      The resin I used was Amazing Clear Cast 1:1,acquired here.From what you responded,I must have applied a not thoroughly mixed layer,it is very tacky.
      As an attempt at stabilizing,what do think about a final thin coat over the not dry areas , intent to stabilize them? Although it is a work of art,the application is similar to bar top finish.The depth varies from 1/4-3/4 inch inch.

  • #10515 Reply


    With regard to a flat pour,I made the mistake of adding an additional pour over the first fairly quickly,thinking they would merge.This was well before the first pour being cured. I am finding that in these areas the top layer is sliding when put vertical…not cured after 3 days.
    QUESTION: will the top coat dry,if yes, how long should I expect?

  • #10519 Reply

    Katherine Swift

    Hello Rob,

    The second layer of resin should have adhered to the first layer of resin assuming you were mixing and pouring the same kind. If they didn’t, then there is something wrong with the curing.

    Without knowing what kind/brand of resin you are using, I don’t know if it should be fully cured after 3 days. I would suggest contacting the manufacturer who should be able to give you that information. I can tell you, however, that if it should have cured by now, giving it extra time isn’t going to help.

  • #10534 Reply

    Katherine Swift

    Hi Rob,

    Thanks for the additional information. It is helpful.

    If your areas are a little sticky or tacky, another layer of resin will cover those fine. If the areas are gooey, then you are going to have to scrape it off and start over. 🙁

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