Why is my resin is ‘WAVY’ & ‘DISTORTED’ after curing?

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    • #10271
      Katherine Swift

      This question comes from Jacob:

      I was hoping to get some advice about an object I cast in clear epoxy resin with a 1% catalyst mix.

      This is the second time I have used resin, the first time it was rather successful and there were hardly any distortions at all, however this time a huge amount of what I can only describe as waves and ripples are riddled all over the inside of my resin object. I am unsure why this happened the second time, and was hoping I may be able to get some friendly advice from yourselves about what the general rules of resin working are if that would be ok?
      I am hopefully going to be able to attempt a second pour in a couple of weeks and would really like this one to go well, as the case and resin are not too cheap to buy.
      The main questions I think would be of most benefit to me would be the following:

      1. Is there a maximum volume or height of resin I should be pouring in each stage? The dimensions of my box are 350x80x80mm ending up with a volume of around 2.5litres of resin to fill.

      2. How long should I wait until I start the next pour? I’m worried I might not be giving the previous pour enough time to cure before I do the next one. I know this can give off some extreme heat and thought that maybe this was a contributing factor to the cause of some of these abnormalities?
      NOTE: I am trying to make the mold look like one solid pour and have been a bit anxious if I leave it for too long it will easily show visible layers.

      3. I’ve been using a heat gun over the resin before and after I pour it in, to try and remove as many air bubbles as possible. Could using the heat gun on the resin too close up and for too long affect its chemical properties and cause some of the abnormalities I mentioned?

      4. My case material is glass, this wouldn’t cause any of the issues I assume?

      5. The room temperature I am using is around about 20 degress C which I believed was a good overall temperature for resin casting.

      I’ve been using a measuring jug for my resin and syringes for my catalyst measuring so I believe these are fairly accurate.

      If there may be any over factors that you think could be affecting my resin I would love to hear them and would be very grateful.

      I’d be extremely grateful for any knowledge and guidance you may be able to provide me with,

      cracked resin

    • #10276
      Katherine Swift

      Hi Jacob,

      I’m sorry to hear you are having problems. I’m happy to help as best as I can.

      I realize you said you were using a clear epoxy resin with a 1% catalyst mix, but I suspect you are using a polyester resin. Most epoxies mix 1:1 or 2:1. It sounds like you are using drops of catalyst per pour? I’m answering your question like you are using a polyester resin.

      First I would start with what the manufacturer recommends for the amount of catalyst to use. With polyester resins, this is usually drops of catalyst per a specific casting depth. (Yes, I realize that’s a little weird.) The thinner the casting, the more catalyst needed because it’s harder to generate heat to cure the resin over a thin surface. The heat produced during the casting is additive as well. This is important because when you go to pour your next layer before the first layer has fully cured, you need to take this into consideration. It is good to do this to minimize lines, but you need to reduce the amount of catalyst used on subsequent layers. The manufacturer should also have recommendations for the amount of catalyst to add in subsequent layers when the first layer has not fully cured.

      What looks like happened here is that your resin got too hot and cracked during the curing process. This is a problem when casting large amounts of polyester resin at once. You should ask the manufacturer what the minimum and maximum mixing amounts of casting this resin are. Mixing too much at once can produce too much heat and will cause the resin to crack.

      To minimize the lines between layers, you can wait until the first layer starts to gel, then pour the next layer. Be mindful that the first layer is curing and generating heat which will impact your next layer.

      Using a heat gun will not affect the chemical properties of the resin, but it does add heat. A quick ‘go over’ with the gun shouldn’t make a difference but if you are using the gun for more than a minute, then yes, that heat is likely impacting your piece and contributing to the cracking.

      Unfortunately, casting your resin in a glass container may also be contributing to the cracking. Polyester resin can shrink significantly, meaning it’s trying to pull away from the glass as it cools. Polyester resin isn’t very flexible, so it could crack.

      The temperature (20 Celsius) isn’t impacting things in a bad way. In fact, it’s a little cool for resin casting. Low 70’s F is what I recommend.

      Here’s an article on polyester resin casting that you should find helpful: https://www.resinobsession.com/resin-resin-resin/polyester-casting-resin

      Good luck!

      • #10324


        Thanks very much for getting back to me! All really useful info!

        I see, I have been trying to look and see if my resin specifies anywhere whether my resin is epoxy or polyester but cannot seem to find any indication, I will take your word for it though.

        They suggest layers of 20mm, although do not suggest amounts for subsequent layers, as can be seen in the following link: https://www.fibreglassdirect.co.uk/amfile/file/download/file_id/159/product_id/31/

        They suggest a maximum of 2kg of resin, however my object needs about 2.5kg to fill, if I pour the layers with larger gaps in time to allow for curing and in lesser amounts do you think this would be ok? Like I said in my previous post, my first pour went almost perfect, with very few distortions. However that was in a plastic container, not Glass.

        I will be more careful with the heat gun on the next pour, I think this definitely contributed to my problem.

        In regards to the issue about the glass, would this not be the case for whatever material the resin is poured into, as it will shrink anyway? The shrinkage is apparently 6%.



    • #10325
      Katherine Swift

      Hi Jacob,

      Polyester resin can also be called fiberglass resin. Based upon the additional information you supplied, I definitely think you are working with a polyester resin.

      Have you asked the manufacturer for tech support? I have never worked with this resin and am afraid I cannot give you the specifics you need for casting a large project such as this. I would expect they could give you specific advice on the amount of catalyst to add per layer and how long to wait in between layers. Yes, while pouring the layers with larger gaps in time will help with excess heat production, you risk seeing your casting lines in between the layers.

      Shrinkage with polyester resin is a problem. I generally tell people to expect 7%. The big issue here is that the resin wants to stick to the glass. If you were casting into something like silicone, it would still shrink, but hopefully would not let it crack as the silicone will release the resin.

    • #10341

      Hi Katherine,

      Thanks for getting back to me. Yes I did contact the manufacturer who stated very similar predictions that you made. These were there comments:

      ”I just spoke with the Aliancys technical services manager about this issue. The thought is the two different container types may have affected the curing stresses differently. As the resin cures typically shrinkage of around 6% is experienced, the plastic container being flexible may have moved with the shrinkage whereas the glass would have remained static. Was any release agent used? Wax would enable release of the resin from both surfaces so shrinkage could occur without being pulled back by the surfaces. We don’t know the volumes poured, but it maybe also a case too much resin in one shot. Try building up with a number of smaller pours.These processes are very difficult to get perfect and usually require the surfaces of the casting to be abraded and polished.”

      So from what both you and the manufacturer have said is my glass is a likely cause to the problem. The manufacturer recommended I use a release agent, however I was hoping to keep my resin protected in this glass case. If I was to apply some release agent to the glass would this not mean that the final casted volume of my object would be of a smaller size then my case, and it would not be pressed against the glass?

      Would you suggest that I use a release agent for this next attempt? I’m pretty sure the glass is the issue now that the shrinkage issue has been pointed out. I just wondered if there would be a way for me to achieve the desired result of a clean resin finish and have me object sealed in a glass case?



    • #10344
      Katherine Swift

      Hmmm. This is a dilemma! We do have a couple of mold releases that I would suggest, but unfortunately cannot ship to you in the UK. I would suggest you try Clare and Kate at resin8.co.uk. They are located in the UK and can hopefully help you with a product recommendation.

      I also don’t know whether or not you would see an air pocket between the cured resin and the glass. If you try this, would you mind letting me know how it goes?

      • #10347

        Hi Kate,

        Yes it seems to be doesn’t it! Ok, I will get in touch with them and hopefully they can help.

        Yeah of course I’ll let you know.

        Thanks again πŸ™‚

    • #85764
      Katherine Swift
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