5 Things You Need to Know Before Using Polyester Casting Resin

polyester resin casting tips
Thinking about using polyester casting resin?

Who wakes up in the morning thinking that? Probably not you.

Then why does it matter?

The problem is that if you go to some of those big box crafting stores (which you shouldn’t — more on that in a minute), you can buy this stuff.

Except crafters don’t understand what they’re buying.

Like resin is resin, right?

No. Never. All resins aren’t epoxy. (But epoxy is resin.)

Polyester is a resin, but it’s not close to epoxy. It’s kinda like your second cousin, once removed, who stands on the end of the third row for family reunion pictures.

If you’ve accidentally bought polyester casting resin (most people) or you want to give it a try (not most people), here’s what you need to know first:

1. The smell is horrible.

I will NEVER use this resin inside my house or office. Instead, I use it inside an enclosed space (like a garage). Then, I leave the garage, close the doors, and don’t reenter for twelve hours or more. I always use a NIOSH-approved respirator for fumes when working with this resin.

If I didn’t have a NIOSH-approved respirator, I would only use this resin outside. I would also have a fan blowing fresh air on me or evacuating air away from the casting. Yes, I realize this is overkill, but at least to me, the smell is that bad.

⭐️ BONUS: Here’s a link to the respirator I use: resin safety precautions

2. This resin is not for beginners.

If you’re new to this don’t use polyester casting resin. It requires more skill.

Why?

  • The pot time is shorter than many epoxies, generally 10 minutes or less. Epoxy resins have a pot time of 20 or more.
  • Polyester casting resin does not mix in a 1:1 or 2:1 formula but instead requires drops of hardener per ounce of resin. If you’re struggling to thoroughly mix epoxy resin, you won’t succeed mixing polyester casting resin.

If you’re a beginner, start with epoxy resin. They are easier to work with and you’ll get excellent resin casting results.

⭐️ BONUS: Here are some all-in-one resin starter kits that are great for beginners.

3. You have to start with the end in mind.

While you can mix a volume of epoxy and use it as you please, polyester casting resin isn’t that simple. The amount of hardener you add is dependent on the depth of the final casting. It seems counterintuitive, but the thinner the casting, the more hardener you need. Thicker castings need fewer drops of hardener.

In other words, you can’t mix the resin, thinking you can pour it into any resin mold you have. You might end up with a resin casting that doesn’t cure or one where the resin heated up too quickly and cracked.

⭐️ BONUS:  Here’s how to figure out how much resin you need.

4. The shelf life on polyester casting resin is no more than 6 months.

While epoxy resin has a shelf life of 1 year or more, six months is the longest you can expect polyester casting resin to be usable. After that, the resin hardens on its own. You may go to use it one day only to find it’s a solid brick.

This brings me back to the ‘box store’ comment. I’ve helped more than one resin crafter who told me that their resin was hard from the first time they tried to use it. That means the resin was older than 6 months when they bought it.

That comes from not rotating stock.

Something Resin Obsession takes pretty seriously. 😉

⭐️ BONUS: Why does resin yellow?

5. The surface exposed to air during curing will remain sticky, even after the resin has cured.

You will either need to sand off the sticky surface or seal it with a layer of resin sealer spray to cover the stickiness.

And this surface will stay sticky indefinitely. I’ve got some pieces that are going on 10 years. And still sticky.

⭐️ BONUS: Here are other reasons why your resin is sticky.

So with all these disadvantages to using polyester casting resin, why would you ever use it?

Polyester resin castings cure very hard. They cure hard enough that you can use a buffing wheel and compound to polish polyester resin castings. You don’t have to recoat with another layer of resin or a gloss spray to get a shiny surface. A few seconds on a buffing wheel is all it takes to get a bright, glossy finish. But, if you drop a polyester casting on a hard surface, it will probably break.

Polyester resin isn’t affected by humidity. It cures well, even in the hot and humid summers of Florida.

Confused by all the resin information out there?

I get it. I felt the same way when I started with resin crafts almost 15 years ago. It’s why I wrote the ebook, Resin Fundamentals.  It takes you from confused to confident with resin in only an afternoon. Buy now and get an email download link in a few minutes.

Unpublished Blog Posts of Resin Obsession, LLC © 2022 Resin Obsession, LLC

 

Like this post? You may be interested in  Essential Tips For Working With Epoxy Resin

97 thoughts on “5 Things You Need to Know Before Using Polyester Casting Resin

  1. For the hardness factor, I would like to try Polyester resin at some time, but.. that time is not now and likely not until I have retired from the day job. I wouldn’t be able to consistently schedule time to do projects for it with only weekends available. Plus, I want to make sure I have an environment where I am comfortable working outside with it. But, oh, the thought of being able to use a buffer to shine it…

    1. It can be exhausting! This all did sound scary didn’t it? I don’t want to scare you away, but want to make sure you have clear expectations on what might happen. (or what could go wrong 🙁 )

  2. Polyester resin was the first I tried. Before that I didn’t know that there is difference in resins.
    I’d like to mention one more problem. On youtobe.com (as usually 🙂 ) I watched as people suggested to use plastic yogurt trays for mixing components. I decided that it’s good idea! What happened? Resin melted the bottom of that yogurt tray…I was lucky that didn’t do this inside my home!!!!
    Thanks for mentioning these problems in article! I good to know i am not alone 😀 After my first failure (when my “masterpiece” remained with sticky surface) I thought I did something wrong. And I did something wrong. It was said in instruction that in order to prevent sticky surfaces, it has to be covered so there wouldn’t be any air in between. Second time I tried to cover it by plastic , but that didn’t help either. The surface remained sticky and thanks to plastic- rough. And that terrible, terrible, terrible smell that don’t disappear for couple of days…

    1. I’m new at this, but would love do it. I have some beautiful old windows that I would like to put in sea glass. How heavy is this stuff? I would be working outside with it. Sound like the way to go with sea glass and window. Seen them in Pinterest.

      1. Hmm. If you put it in thick layers, yes, I would expect it to be heavy. Were you hoping to replace the windows with resin or use the resin on top the glass already in the windows?

  3. After years of using epoxy resin I tried polyester earlier this month. Smell is bad, smells like rubber cement x 100. Much harder to work with and goes right from very liquid to gel, unlike epoxy that gets more syrupy with time. But I have to say my deep castings for cabochons ended up so beautiful and clear, not a bubble in sight. For deep castings polyester is definitely the way to go. For anything else, stick with epoxy. In my humble opinion.

  4. I have actually just started working with resin period and not knowing much about the difference I chose the polyester. I had a few trial an errors, but I so far I think I found that using about 10 drops of catalyst per ounce no matter what I am making has somehow worked out everytime for me. Yes it stinks and does gel up quickly, but it seems to turn out beautiful for me everytime now that I have worked out the bugs.

    1. Same here. Only tried polyester, and non experience with epoxy. My pieces turn out beautiful every time. Just a few drops of hardener will cure each project. Curing time varies between 1 hour and 5 days. Just a few drops in a large batch of resin will take longer to cure, but all airbubbles will be gone. The end product is hard, and hardly any scratches over time. But indeed the smell is bad. True!

  5. I have a question, do you know if this is safe for long skin exposure? I wrote envirotex lite and asked about making gauges for eats and they advised me it would not be save for long skin exposure. Would this type of resin be?

  6. I’m having a rough (excuse the pun) time getting a clean finish. I didn’t know about the different resins and encased some sentimental flowers in a bracelet. It’s perfectly dry not cloudy however I tried to sand then buff the seams on the bracket and now I can’t get it to go clear again!!! It’s a cloudy scratched mess no matter how much I buff. How can I fix this?!

    1. I have good results with a product by Mod Podge called “Dimensional Magic”. After you buff or sand, paint a thin layer of DM on your piece, and you should have a nice, shiny surface. It’s quite hard, too. You can also use it to “dome” surfaces. If you like a thick dome, do it in layers, because if you drop too thick a layer, it will dry cloudy.

      1. I want to cast my wedding bouquet (after several practice rounds). Because of the depth, should I use polyester resin? Which resin is best for “larger” projects? And where is the best place to buy this much of it?

        Thanks for all your amazing insights!

  7. I’ve been using polyester for a few months now and after lots of trials and errors I think I’ve cracked it! I added a slightly bit more hardener and I’ve found I have no sticky layer! Yay. Definitely makes the finished result more brittle but it’s fine for smaller pieces like pendants and it’s soo crystal clear

  8. A quick warning about Polyester Resin. Its much harsher then Epoxy. Polyester will eat through plastic cups so you have to be careful what you used to mix it in. It can also take the finish right off some of your embedded objects and change the colour of some pigments.
    It does dry super clear and hard. I personally love using it and its cheaper the epoxy too! But it does take a bit of prior knowledge of what it could react to before you find it just ate your favorite embellishment.

    1. It will not eat through most clear plastics (ex., polypropylene). It will, however, eat through polystyrene, which is what most cheap white plastic cups are made of.

  9. Hello, I am working on a shoe design and I really need to make a pair of clear high heels, what kind of resin should I use to make the heel part, keeping in mind that needs to be resistant to weight?

    1. ….keep in mind that the heel needs to be resistant to weight….
      I’m pretty sure she’s referring to the ‘weight’ of someone wearing them… I’m curious too. What resin would be best for making a clear heel?? Or even an entire shoe 👠 ?? Glass slippers yipeee! Could both work?? I know they make acrylic heals that would be the same look. Also, this might be a stupid question but, is acrylic the same thing as resin??
      Thank you!

  10. Hello, I have a question about stability. I cast a resin panel (approx. 5/8″ thick) with some rock embedments for a client and was just called back (after 4 years) to see that is has noticeably warped. It’s approx. 24″ a 30″, displayed in a wall opening (like a window) and over time has become convex – deflecting somewhere between 1/2″ and 3/4″ over 24″. Any ideas what is causing this and anything I can do to repair and/or arrest the movement? Love to hear your thoughts.

        1. Hmm. I don’t have a good answer for you on why this happened. Unfortunately, there isn’t going to be an easy way to fix it. You can try to cast another layer on the front and back to even it out, but without some support on the sides, this will likely happen again.

  11. What a dilemma: A couple of years ago I was given 2 large tins of XOR Crystal Polyester Resin and hardeners etc. and, because I did not want to waste any resin, I thought I’d wait until I had a good idea as to what to use it for. Now, after coming across your excellent website, I decided to give it a go; The resin inside the tins seems very hard, but clear, with a few walnut size snow-white crystals on top…
    I guess I can not make it liquid anymore, so, hopefully it is rock-hard all the way through, then I can at least put it on the milling machine and make some cubes or whatever shapes out of it.
    Sadly, I didn’t know that that stuff doesn’t keep….

  12. Thanks for the info. Few questions. 2nd attempt. :/ using epoxy for 6 months and my 3D molds get Sri bubble holes in the finish product at top. Even in pressure pot. My molds are 80+ml (1-2”deep). My epoxy is fine w anything under 1” but after that the craters develops. Annoying. I’ve tried so much. Would you suggest any other type of epoxy or just this polyester type? Working outside isn’t really an option down here in sofla. High heat and humidity. Also. I guess w the quick set I wouldn’t need to worry on sealing the edges of the mold but would. I still be able to drop inks in? If it’s setting in 10 min Is that when it’s ready to demold? I didn’t see the demold time. Thank you.

  13. hello, ive used this a lot as well for cabochans into pendant trays. Have you found that they get scuffed up on the surface? I make mine to sell and I find that when i travel with them, theres always several that are unsellable from being bumped around, thx.

    1. I can’t say that’s been my experience. Polyester resin should cure to the hardness of glass and not scratch easily.

  14. So my projects cured with a rippled finish? Any ideas why? How can i fix the finished pieces so they look like glass? FYI Project is coasters.

  15. I’m planning on casting roughly 4” x 6” (d x l) cylinders for long-term salt-water submersion under pressure. Would polyester resin be a good/the best material for that?

    More questions:
    2) My embeds are extremely heat sensitive. I’m presuming I will need to cast with a channel (~ 1”)1 to insert the embeds into the center and then backfill with a plug. The embeds will be enclosed in a glass or plastic container. What concerns might I have with this plan?

    3) If I go with the cast-embed-plug method in 2) above, will the plug bond chemically with the surrounding material? Will it be visible? I plan to add a bulge in the channel via casting or drilling to provide physical resistance to the plug popping out and an insulator between the plug and the embedded item. Do you foresee any problems with this plan?

    4) Is it possible to “swirl” color in the polyester resin so I end up with ribbons of color throughout my clear cylinder?

    5) Finally 😂, is it possible to embed graphics on a clear substrate (e.g., a printout) in the polyester resin? What do I need to consider re: substrate or ink? Alternately, how would I put a hologram in this?

    Thanks so much for your help. This place rocks!

    Boomer

    1. I’m afraid I don’t have any experience using polyester resin for constant salt water exposure. I don’t know how well it would hold up.

  16. I’m new to casting and have started with clear epoxy. Seems easy enough but the moulds I want to cast need to be <3mm thick. I've found that epoxy is not rigid at this thickness, but I'm wondering if polyester would be?

  17. I want to cast a ring dia 4: which will hold strand of MS wires, Main reason for mould is to hold these wires to make a wheel brush.
    what will be best choice?
    I am going to do this first time.Please help
    Thanks

  18. Why my polyester resin released gas-like smoke and fumes? was it normal or i did something incorrect? I used Pp corrugated sheet for molding (and it also heated).

    Thanks,

  19. I am looking to make a few jewelry pieces. Earrings to be exact. I am well aquanted with epoxy, but am liking the clearness of the poly. What would you suggest for a clear, skin safe, not extremely fragile pair?

  20. I don’t think this is a fair assessment. I make various resin items, mostly jewelry, and have used both poly and epoxy. I started with epoxy like everyone suggested and I HATE it. It bubbles, its soft, it doesnt shine well, and it takes FOREVER to cure. Waiting 7 days to be able to turn a piece on the lathe is absurd…and then when it does get to the the lathe it fogs and bends. Epoxy is garbage and the finished products look cheap and don’t hold their integrity as they yellow and fade over time. Yes, poly requires the use of a catalyst. This is no big deal at all. As a matter of fact, you can use the catalyst to have a better control of your cure time. Imagine my amazement going from 7 days curing with epoxy to 1 hour with poly! What a huge improvement to piece turnaround! Yes it smells. It’s a chemical. Let’s not be dramatic. Yes cure time is far less than with epoxy. Prepare yourself first then pour. Dont mix up several ounces with no plans. None of these issues above are actually issues. Poly is far superior to epoxy in nearly every way when looking create professional looking pieces in a timely manner.

    1. Hi Mikki, what specifically about this article do you think isn’t fair or accurate? It sounds like you have a lot of experience using polyester resin. Please, tell us more.

  21. I just bpught this clear polyester castin resin, i read the chart and been looming online for another chart, but it doesnt tell me how much catalyst I need for ounces, just for how think you want the layer. I’m doing a 2inch sphere with a flower and it holds 6 ouncesbut dont k ow how many drops to use

    1. Hi Rache, if you can’t find that information with the casting kit, you will have to reach out to the manufacturer for that information. Unfortunately every kit is different.

    2. As mentioned by Katherine, check the label or manufacturer’s website, since most polyester resins come with some accelerant mixed in (not always the same amount).

      However, the vast majority of polyester resins require between 1% and 3% catalyst, depending on temperature (lower temperatures need more catalyst) and how fast you want them to cure (the faster they cure the more likely they’ll crack, so slower is generally preferable unless you’re in a hurry).

      A “drop” isn’t really a fixed amount (depends on the eyedropper), so get a graduated pipette and make a test with about 1.5% catalyst (i.e., if you’re mixing 180 ml – which is approximately 6 ounces – of resin, use about 2.7 ml of catalyst), unless you’re somewhere very hot, in which case use only 1% (1.8 ml).

      If that takes too long, try about 2% (3.6 ml, for 180 ml of resin), and then 2.5% (4.5 ml).

      You generally won’t need to go above 2.5% unless it’s very cold (and, if it is very cold, exposed surfaces will always remain sticky, so you’re better off letting it cure somewhere warmer, instead of adding more catalyst).

      If you can’t get a graduated eyedropper, assume 1 drop = approximately 5 ml (but really, using a graduated eyedropper makes things more controllable, and you can get disposable graduated eyedroppers for a couple of cents a piece).

  22. I have never used resins of any sort and now doubting that I even can for my project but thought I’d ask. Spray painted bullet casings glued to plywood and set in angle iron framed coffee table. Very small crevices between casings. Depth from wood to top of table just shy of an inch but from top of casings to top of table approx 1/8″. Is it even possible?

    1. Hi Michelle, you have a lot going on here!

      Resin can work for this project, but I think this situation is best suited for a one-on-one consulting call where you and I talk back and forth about what’s going on so I can give you the best advice possible. A 15-minute consultation call is $20. I do them by video so I can have a chance to see what you are working on.

      If you are interested, please send a message through the ‘contact us’ page and I can get this going for you.

      Sincerely,
      Katherine @ Resin Obsession

      1. Hello. We are casting something 170mm high amd 110 mm thick. The heat is tremendous in the silicone after about an hour. With the first attempt we took it out of the mould and then and all of a sudden it overheated and cracked significantly. When working with this volume of resin (it’s around 700g) how much catalyst should I use and when curing should I leave in the mould and for longer? I will the exithermuc reaction be slowed down if I leave it in the silicone sleeve for longer? Thanks! Any tips with working with this volume of resin appreciated.

  23. I work with Dollhouse Miniatures. I would like to make “bottles” for Lotion, perfume, etc. using gelatin
    capsules and resin. I have been told to use Envirotex Lite. Is there something better? The largest are .75″ tall and .25″ wide. The smallest are .4″ high and .13 wide. Just think of the vitamin supplements you take!

    1. Hello! I have a very special resin project I want to do for my stepson. His mother just passed and I have some of her cremains and a dried rose from the funeral that I want to add to the Castin Craft Polyester resin in a 2.3 inch cube. I have been researching like crazy and want to be sure I do it perfectly for him. I will obviously practice first.

      I have 32 oz of the resin. I am confused because it says to add a drop of catalyst to each layer for single layer pours and the largest layer is 1 inch. Does that mean I have to pour the cube in 2 layers?? I am really confused.

      I also have a tiny piece of an index card that I printed where she had written “love” and I put modge podge over it. I am hoping to put it down as well as some powder pigment to make some swirls. Since you have more experience in this, do you think it may work?

      Thank you 🙂

      1. Yes, 1 inch is the deepest Castin’ craft recommends pouring the polyester resin. As for sealing the paper to put in resin, mod podge does work.

  24. Thank you! Does that mean I have to pour a 1 inch layer and wait and pour another? I am not sure how long to wait between layers.

  25. Ok, I just attempted my first one! However, how in the world do u clean your mixing cups?? Mine are silicone. I tried water from the hose outside and nope ..not happening. Any ideas?

  26. Hello! Did anyone ever tried using pressure pot for casting polyester resin? I’ve tried it, but the results make the surface of the resin to wrinkled and sticky, like some tree bark from alien planet , does anyone know the cause?

  27. I pouring something that is 9″ deep by 12″ , a round tube. There is an object inside. What is the best resin to use and can I pour the whole depth at once.

    1. Hi Ashley, you will need a deep-pour casting resin and stay within the recommended guidelines for the maximum amount to pour at once.

  28. Hi Katherine. Thank you very much for a very informative article. I have just recently started casting with polyester casting resin, doing a small little table with wood imbedded into the resin. came out really well to my surprise. with all the info i also found on your page, i am rather excited for my next project. thank you again.

  29. Hi, I’m thinking of making a mailbox POST out of polyester resin. It would need to be 45in high and 2 in diameter. 2 questions what can I use as a form and is this a feasible idea?

  30. HELLO ! Everyone Im doing a concrete table with a couple of rivers running thru it. My ? is . will it bond to concrete ?( concrete is cured completely and sealed on top only but not where the resin make contact ) Right now the table is all one pc. the river section vary from 1/2 in to 3/4 in depth and the width is anywhere from 1/2 to 2in and 2ft in length. Would I be able to use this productto make the rivers? Oh also Can it be mixed with mica powder:? Thank you

  31. Hello!
    I plan to cast polyhedral dice (each approx 1.5cm in height) using polyester resin. Considering the properties/durability of this variety of resin, what is the likelihood that my dice will shatter/chip when thrown against a tabletop?

    1. Hi Diva, I wouldn’t expect them to chip on a gameboard, but they might if they are dropped on a hard surface.

  32. I don’t know if this has been asked and answered.
    I’m brand new to resin, but a veteran nail tech. I’m very used to working quickly with products before they cure.
    For a nail art competition, I want to make a clear resin hand holding a cellphone.
    I’m thinking of casting in alginate.(silicone is sooo expensive $$$)
    I know epoxy resin doesn’t like the moisture in alginate, but I’m wondering if polyester resin would do OK.
    I don’t have a pressure pot, and am a little worried about bubbles.
    Any advice you can give would be greatly appreciated.

  33. Polyester resin is a particularly dangerous material because of the fumes that it gives off in the unmixed state. Short-term effects of these fumes are: dizziness, nausea, skin irritation.
    Mixing with the catalyst/hardener can have the same immediate effects but much worse; from eye, skin and respiratory irritations to permanent damage and death.

    Documented Long–term effects can include
    nervous system damage, deadly allergic reaction, respiratory system damage, asphyxiation, decreased fertility, harm to unborn babies, cancers.

    IF YOU DONT TAKE AWAY ANYTHING ELSE from my post, please hear this: read BOTH the safety data sheets for the resin AND the hardener or catalyst. If you do an internet search or find them on the companies website, the safest product sds with usually be listed first. Most people – including me not too long ago – was satisfied with the safety of resin after reading the resin sds. But then I noticed there were multiple sds for the same product. I clicked on the second – the hardener/catalyst. Hmmm. Not so safe, pretty scary to be honest.

    Then I googled and read and researched. I learned these arts and crafts materials, these fun products available at hobby, big box, art and craft stores did not have proper warnings and were not safe and benign when used the way most consumers and instructors used them. Without proper safety equipment.

    Read all the safety data sheets, then search for recalls, violations, complaints etc on the Consumer Protections website. After you have all the facts, you CAN safely work with polyester resin.

    Wear chemical resistant gloves,
    wear clothing that completely covers your skin, head to toe. NOT synthetic material – it will catch on fire and melt/become your skin. Trust me on this one. I’m an ER nurse. I’ve seen stuff.
    Enclosed safety goggles,
    a 1/2 face respirator mask with chemical filters (dust, viral, hepa filters won’t cut it) and excellent ventilation; outside or inside with exhaust fans.

    Always have a chemical fire extinguisher close by. And please – no torches or heat guns with polyester resin! The flash point is much lower than other materials.

    I don’t use polyester or urethane resins, this is how I work with epoxy and UV resins. It may be overkill… I hope it is. But I’m going to be as safe as I can be; I want to be healthy and strong for my family for years to come. I want you to be as well.

  34. Hi, I’ve only recently started to use Resins, and had been using Epoxy, but I thought that Epoxy is very costly and I looked (and ordered) polyester, due to the cost factor. Having read the comment’s here, I’m wondering if I have made an error. The polyester arrived yesterday, so I haven’t opened it yet. Should I be returning it in exchange for another resin. Thank you, Joe

  35. Hi
    I am working with polyester resin and I pour mix of resin filler … in mold . But I do not have idea for demolding ?
    Normally what time I should demold my part from fiberglass mold ??
    After gel time or exoterm or after cooling ?
    Pls help me
    Tanks

  36. I goundbpolyester is so hard it is brittle, and tends to chip (especially when I turn on the large). Polyurethane reacts with wood and forms nasty bubbles where they touch, so not good for mixing with wood. Epoxy seems okay in both respects, based on first tests.

  37. Hi there! I’ve only read a couple of your posts but you seem like the right person to ask about my project.
    My sister requested I make a resin globe with a flower from her wedding bouquet inside, so the requirements I’m assuming I need are crystal clear resin and ability to cure with a depth of about 4 inches. After looking at your posts I’m torn between epoxy and polyester.
    As far as I can tell:
    Epoxy- good for beginners, can be clear, but may be soft for deeper molds(?)
    Polyester- super clear, can handle buffing, good for deep molds, but bad for beginners

    As a beginner… I’m lost. What’s considered deep for molds? Does polyester have to be buffed with a machine or can it be done by hand?

    Any advice you have would be GREATLY appreciated! Thank you in advance <3

  38. I would like some advice if its safe to use polyester resin as my base (1st layer). Then when it is fully dried, is it safe to layer is with UV resin?

  39. Hello! I’m considering make a side table with a slice of a tree that has split in half and using resin to hold it together. Would this type of resin be a good thing to use?

  40. Hi! I have a project that I bought this resin for and now am having a hard time pulling the trigger on pouring due to the complexity of it. I am making a cosplay wizard staff with a crystal made of resin at the top. I have already made a silicone mold of the shape I want for the crystal, it come to be about 26oz to fill the mold, and from top to bottom is about 16 inches. So my main issue is that with the instructions the layering become obscured when the shape is a bit pointed at the bottom of the mold and widens closer to the top of the mold. I am worried that it will heat up too fast and crack or start burning as it seems to be such a bigger object then most people do! So my questions are
    1. How would I go about with the amount I pour at a time and how long in-between pours should I wait?
    2. Does the resin crack so easily that hollowing it out after it cures would not work? As I would want to put lights inside and was thinking of hollowing it out with a drill press little by little when its fully cured and removed from the mold

    Thank you Sam

    1. Hi Sam, yes, overheating and cracking is a potential problem for your project. Here’s a few articles to guide you: Gel phase – https://www.resinobsession.com/resin-frequently-asked-questions/what-is-the-gel-time-of-resin/ Deep pour resin tips — https://www.resinobsession.com/resin-resin-resin/deep-pour-resin-casting-tips/. While you can remove some resin after it cures, hollowing it out as much as you are talking about may affect the structural integrity of the structure. If you want a hollow structure, try a mold that casts that way.

  41. Hi, I use Polyester Resin to make all of my jewellery. It has taken me 4 years (and still learning) to find out what it can and cant do. I live in New Zealand and resin here is extremely expensive due to it having to be imported and go through customs with extra taxes etc and extra caution as its labelled a dangerous substance. I cast it to wood (must be a hard wood) and then shape by hand, sand, buff etc. I have tried Epoxy resin a few times but it never sets, I have studied a lot of literature on the subject and think that as we generally have a very high humidity (sitting around 85%- 98%) that may be one of the causes. I have recently purchased some digital scales so will try again once winter is over and we have temperatures of around 20C. I did wonder about building some sort of drying room, or maybe using a heatmat that is used for plant propagation. I will keep trying, I won’t let it beat me!

    1. Hi Debbie, how frustrating that your choices are limited. One of the other things about polyester is that is shrinks the most when curing.

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