Author Topic: Resin Casting Issues - Tips?  (Read 5072 times)

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Offline klaushouse

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Resin Casting Issues - Tips?
« on: Sun, 13 August 2017, 00:03:33 »
I've been really struggling with the urethane resin and was hoping some folks might have some advice for me.

My resin refuses to cure leaving this semi gelatinous sticky mess which pseudo ruins my molds because as far as of yet I can't even get them fully clean. :(

I am using a simple 1:1 Smooth Cast 326, but every single time no matter how long I stir either one of those things happens:

-I stir (anywhere from 1-5 minutes) but it remains separate like because of the higher viscosity of part B it won't blend even for a second. This is where I often get the goop.

-Once I stirred it so viciously that it basically all turned to bubbles like the top of a root beer, out of boredom I tried it in the mold and it actually hardened very nicely and after I trimmed the excess it made a piece - although completely a mess - actually turned into my only savable plastic casting so far. (pictured below)

Am I doing something wrong? Am I missing a crucial step or simple process making the 1:1 mix easier? Watching videos online it seems like they are two very simple liquids that basically mix with no work. I'm utterly confused. :(


Offline KeLorean

  • Posts: 167
  • Location: Space Coast, FL
Re: Resin Casting Issues - Tips?
« Reply #1 on: Sun, 13 August 2017, 17:14:28 »
measure carefully. scrape sides of mixing cups to be sure to get all of the two halves. get a cheap hygrometer. im using this and has been accurate enough. https://www.walmart.com/ip/Hygrometer-Indoor-Outdoor-Measures-Humidity-Thermometer-Temperature-Meter-Temp/141153327?wmlspartner=wlpa&selectedSellerId=709&adid=22222222228042687553&wl0=&wl1=g&wl2=m&wl3=107035651517&wl4=aud-261800281660:pla-297390748877&wl5=9011831&wl6=&wl7=&wl8=&wl9=pla&wl10=112343202&wl11=online&wl12=141153327&wl13=&veh=sem If the humidy reading is over 50% that mean moisture is contaminating your mixture. another issue could be temperatures. if it is really cold where u are then it could prevent curing. i couldnt tell u what temp that is bc its never been an issue for me. it is also possible that u just have a bad batch, BUT most likely it is moisture, inaccurate measurements, or incomplete mixing. when the catalytic process is happening the mixture will bet warm. if u are using paper cups like i am, you'll be able to feel the heat through the cup. i take that as a sign that i have mix it up plenty. hope that helps. let me know if that works. cheers.
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Offline Findecanor

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Re: Resin Casting Issues - Tips?
« Reply #2 on: Sun, 13 August 2017, 17:29:47 »
This problem could occur if the ratio between parts A and B is not completely 1:1. I lost about every third cast before I got myself a sensitive scale so that I could measure each part to a fraction of a gram.

This happens of course more easier the smaller batch you are mixing. So if you have more than one mould, you could make sure to cast in multiple moulds at once as an excuse to mix a larger batch of resin.
« Last Edit: Sun, 13 August 2017, 17:33:21 by Findecanor »

Offline KeLorean

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Re: Resin Casting Issues - Tips?
« Reply #3 on: Sun, 13 August 2017, 20:44:40 »
This problem could occur if the ratio between parts A and B is not completely 1:1. I lost about every third cast before I got myself a sensitive scale so that I could measure each part to a fraction of a gram.

This happens of course more easier the smaller batch you are mixing. So if you have more than one mould, you could make sure to cast in multiple moulds at once as an excuse to mix a larger batch of resin.
this is a very good point. when i discuss doing resin casts of less than 3ml, the smooth-on resin distributor in my area gets really bug eyed. they warn me that the smaller the mix the more exaggerated any inaccuracies will be.


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Offline klaushouse

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Re: Resin Casting Issues - Tips?
« Reply #4 on: Mon, 14 August 2017, 00:44:30 »
Well my smallest mold I mixed 20ml and I use little beakers with actual markings on it.. I feel like it must be my mixing somehow but not sure how to get it better without turning it into a rootbeer float. Will use suggestions and let you guys know!

Thanks guys! :)

Offline CompileWithStyle

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  • Location: Orange County, CA
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Re: Resin Casting Issues - Tips?
« Reply #5 on: Mon, 14 August 2017, 20:28:52 »
I would always guess one of the following scenarios has occurred:

  • Was not left to cure long enough - the rule is the smaller/thinner the thing the longer the cure for most resins
  • Humidity or temperature are not right - too humid or too cold/hot - or temperatures in environment are changing too much - most things want low humidity and 70 degrees
  • Inaccurate mix due to ratios or mixins - mixins being pigment / dye / ink
  • You are using old materials - they have a limited shelf life, if they change color - they are going off or have gone off

I also recommend you do not come into contact with materials that are curing.  I have seen something that is halfway curing just go off the rails because someone touched it at some point in the process with their actual fingers.  The environment in which it cures is crucial.  To give you an idea I always cure in my garage - I live in Socal so I have lower humidity and a more consistent temperature in my garage than in my house.  My house is likely to have much more humidity due to all the water usage inside.

I have had things take longer to cure or never fully cure when the above scenarios have happened.  A great way to test these out is to purchase a silicone mold and test with it.  I have one that is an object I love using for pour off, meaning extra materials are used in this mold so the plastic does not go to waste.  You can use this to validate your process and materials.

I do not use a scale but I eyeball using measuring cups, rice, and a permanent marker.  I use easy cast clear resin generally for my projects and have had great results.  Most of them are not key cap based and are more sculptures I have made and then cast.  The keys I have done have been the WORST to cure, they are thin and the materials have to have a chemical reaction to harden, the less material the less reaction.

Also make sure you use two cups for part A and part B - do not mix Part B into Part A but rather poor A into B.  Don't try and be cheap about it, scrape the sides.

Also ensure the gloves you are using are made of nitrile.  If you are using anything but there is a high chance that you are causing the chemical reaction to fail.  They are sensitive and you need to make sure you take absolute care when dealing with the reaction you are creating.  Although they do not discuss this often in the terms of chemistry, this is actually what you are doing - a reaction between two chemicals.
« Last Edit: Mon, 14 August 2017, 20:34:23 by CompileWithStyle »
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Offline klaushouse

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Re: Resin Casting Issues - Tips?
« Reply #6 on: Thu, 17 August 2017, 00:00:09 »
Thanks for the tips Compile!

I'm going to be trying to mix larger quantities in the way you told me. I'm going to get the moisture/temp isn't the issue as I got the one to cure completely just all bubbles.. I am inclined to say user error is the issue. My local sculpt shop told me that anything under 500g I should be weighing not trying to do the 1:1 volume so I'm just gonna make over 500g of it and try to pour in multiple molds and use it all.

I'll let you all know how it goes, my $ynth just came in too so this is great timing I'm very excited!

Offline Kenda

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Re: Resin Casting Issues - Tips?
« Reply #7 on: Thu, 17 August 2017, 00:58:10 »
- for curing problem, i think it's the ratio or it's not mixed evenly
- My casts with urethan resin also form lots of bubbles because of humidity issues. I gave up and use epoxy now. Longer curing time but much easier to control


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Offline klaushouse

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Re: Resin Casting Issues - Tips?
« Reply #8 on: Thu, 17 August 2017, 01:02:35 »

Also make sure you use two cups for part A and part B - do not mix Part B into Part A but rather poor A into B.  Don't try and be cheap about it, scrape the sides.


Out of curiosity does it have to be A into B? Is there a particular reason?

- for curing problem, i think it's the ratio or it's not mixed evenly
- My casts with urethan resin also form lots of bubbles because of humidity issues. I gave up and use epoxy now. Longer curing time but much easier to control


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What kind of epoxy are you using? What kind of finish is coming out?

Offline Kenda

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Re: Resin Casting Issues - Tips?
« Reply #9 on: Thu, 17 August 2017, 01:15:20 »

Also make sure you use two cups for part A and part B - do not mix Part B into Part A but rather poor A into B.  Don't try and be cheap about it, scrape the sides.


Out of curiosity does it have to be A into B? Is there a particular reason?

- for curing problem, i think it's the ratio or it's not mixed evenly
- My casts with urethan resin also form lots of bubbles because of humidity issues. I gave up and use epoxy now. Longer curing time but much easier to control


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What kind of epoxy are you using? What kind of finish is coming out?
Any epoxy resin is good to go. The finish is silky smooth


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Offline SKD

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Re: Resin Casting Issues - Tips?
« Reply #10 on: Sat, 19 August 2017, 14:31:38 »
Sometimes I make single caps, and measure as low as 1.5ml part A and part B. If you're not using a pressure pot, heat up your molds, but expect lots of bubbles with 326. At 3ml the resin does not generate enough heat for it to cure properly, the heated up molds help with this a bit. Without the assistant of heat at small ml the caps will never cure to as hard as they could be.

Also get yourself one of those small jewellers scales, that measures at 0.01ml increments. I have a cheapo one and it's been great. I don't suggest measuring by eye using the scales on the side of measuring pots for small quantities.

Your part A and B not mixing properly, I have never experienced that before. You shouldn't need to stir the resin around for up to 5 mins long. After 5 mins the resin would have started turning jelly and at that stage the resin is not usable.

If you want bubble-less or next to no bubbles without pressure pot, you probably want to use a very long curing time resin instead.

Offline klaushouse

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Re: Resin Casting Issues - Tips?
« Reply #11 on: Sat, 19 August 2017, 18:29:23 »
Sometimes I make single caps, and measure as low as 1.5ml part A and part B. If you're not using a pressure pot, heat up your molds, but expect lots of bubbles with 326. At 3ml the resin does not generate enough heat for it to cure properly, the heated up molds help with this a bit. Without the assistant of heat at small ml the caps will never cure to as hard as they could be.

Also get yourself one of those small jewellers scales, that measures at 0.01ml increments. I have a cheapo one and it's been great. I don't suggest measuring by eye using the scales on the side of measuring pots for small quantities.

Your part A and B not mixing properly, I have never experienced that before. You shouldn't need to stir the resin around for up to 5 mins long. After 5 mins the resin would have started turning jelly and at that stage the resin is not usable.

If you want bubble-less or next to no bubbles without pressure pot, you probably want to use a very long curing time resin instead.

I just finally got to make another batch today, and made a few more molds so I can just make a "large amount" of resin to see if that was the issue. Made about 6oz worth and only poured in roughly half into the molds, the other half i left in the container to see if that stuff would harden differently than anything in the mold. I'll find out soon! I have a few molds all of fairly different sizes and thicknesses so it might help shed some light on the issue. Once poured, the excess in the cup got really hot and started fusing within 10-20 seconds so I imagine the same happened in the molds and hoping for a better outcome. It's been a few hours but I'm going to let it sit a few more hours just to be insanely safe. (cure time is really only 60 min)

Offline CompileWithStyle

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Re: Resin Casting Issues - Tips?
« Reply #12 on: Sat, 19 August 2017, 18:50:35 »

Also make sure you use two cups for part A and part B - do not mix Part B into Part A but rather poor A into B.  Don't try and be cheap about it, scrape the sides.


Out of curiosity does it have to be A into B? Is there a particular reason?


The instructions I have read for my materials and the book I have on mold making/casting both state to poor A into B (A being material and B being the activator) when working with resins, I have done the reverse B into A and I have also mixed A then brought B in and mixed in 1 cup.  All the results I have had so far reinforce what the book and instructions shipping with my materials are saying.  I seemed to have a higher chance of failure not following this path.  This could also be confirmation bias or something as well - I can't give you the specific reason.  My thoughts are that slightly more hardener than material is better than more material than hardener - which could be the result from not being able to fully empty A 100%.

In the case of the resin I am using it requires that part A be mixed (resin) prior to hardener being being combined (Part B).

Now saying this - always read the data sheet for whatever materials you are using as they can vary wildly.  In fact thinking more about it I have also seen materials that require the inverse of this, but they are not the materials I've been using.

The materials I have been using even state to not use the same stirring stick from Part A to combine A into B. 

In the end the safest bet is follow that datasheet :)

Best of luck!
« Last Edit: Sat, 19 August 2017, 18:53:17 by CompileWithStyle »
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Offline klaushouse

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Re: Resin Casting Issues - Tips?
« Reply #13 on: Sat, 19 August 2017, 19:05:46 »

Also make sure you use two cups for part A and part B - do not mix Part B into Part A but rather poor A into B.  Don't try and be cheap about it, scrape the sides.


Out of curiosity does it have to be A into B? Is there a particular reason?


The instructions I have read for my materials and the book I have on mold making/casting both state to poor A into B (A being material and B being the activator) when working with resins, I have done the reverse B into A and I have also mixed A then brought B in and mixed in 1 cup.  All the results I have had so far reinforce what the book and instructions shipping with my materials are saying.  I seemed to have a higher chance of failure not following this path.  This could also be confirmation bias or something as well - I can't give you the specific reason.  My thoughts are that slightly more hardener than material is better than more material than hardener - which could be the result from not being able to fully empty A 100%.

In the case of the resin I am using it requires that part A be mixed (resin) prior to hardener being being combined (Part B).

Now saying this - always read the data sheet for whatever materials you are using as they can vary wildly.  In fact thinking more about it I have also seen materials that require the inverse of this, but they are not the materials I've been using.

The materials I have been using even state to not use the same stirring stick from Part A to combine A into B. 

In the end the safest bet is follow that datasheet :)

Best of luck!

Thanks again! Today's pour I followed your advice and I saw a drastic change in how easily they mixed. Hope it yields better results! Will post and let you all know today!

Offline klaushouse

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Re: Resin Casting Issues - Tips?
« Reply #14 on: Sat, 19 August 2017, 21:04:11 »
Good news! Things worked a lot better this time, everything cast very nicely. I made a few mistakes with the keycap (not using enough lube) so I lost a bit of the shape of the key but overall as the test I wanted it to be, super success! Really happy, no problems. I'll post a bunch of pictures just because I'm happy. The last one shows the difference between my old pour and new one, and how much clearer it's gotten. :)

Offline KeLorean

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Re: Resin Casting Issues - Tips?
« Reply #15 on: Sat, 19 August 2017, 22:04:35 »
Good news! Things worked a lot better this time, everything cast very nicely. I made a few mistakes with the keycap (not using enough lube) so I lost a bit of the shape of the key but overall as the test I wanted it to be, super success! Really happy, no problems. I'll post a bunch of pictures just because I'm happy. The last one shows the difference between my old pour and new one, and how much clearer it's gotten. :)
looking good klaus. your well on your way. im glad we could help. your excess ghost guy is cool too. btw, i love your work area. it looks depressingly plain and lonely. haha! i just get sick of all of these pics of people who clean everything to make a picture of their garage. a garage/basement is meant to look like a work area.


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Offline klaushouse

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Re: Resin Casting Issues - Tips?
« Reply #16 on: Sun, 20 August 2017, 13:57:05 »

looking good klaus. your well on your way. im glad we could help. your excess ghost guy is cool too. btw, i love your work area. it looks depressingly plain and lonely. haha! i just get sick of all of these pics of people who clean everything to make a picture of their garage. a garage/basement is meant to look like a work area.


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Hahaha thank you. I live with roommates (awesome albeit) so I often look for a little solitary/lonely place to vibe out, which I think I've accomplished to specification. :)