Author Topic: Resin Casting and Harmful Vapors  (Read 10935 times)

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Offline KeLorean

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Resin Casting and Harmful Vapors
« on: Sat, 12 August 2017, 00:50:39 »
Recently, a new caster asked me if there were negative affects to not wearing a respirator while using urethan resin.  Another new caster told me that he was using Smooth-Cast 326 but didn’t know what kind of resin it was, so I decided to post this discussion.  I myself are pretty new to resin casting, so I’m writing this to open the discussion.  Please correct me if you know any of this information to be inaccurate or misleading.  Thanks.

Many of us casting artisans out of resin are using urethane resin.  I’m sure some people are using other stuff, but I’m addressing urethanes.  The way I understand it, the term urethane (when talking about resin) is just short for polyurethane resin.  (There is such thing as urethane compounds, but it is something quite different, which adds to the confusion.)  For instance, Smooth-Cast 326 is a common resin used amongst our community.  Smooth-On has it listed under Urethane Resins.  However, when you look at the product Safety Sheet (which is located on their website: ) you will notice that the General Use description for both part A and B are "Polyurethane Elastomer.” 

Now, if you call Smooth-On and talk to a technician, such I have 3 times, they will tell you not to inhale the vapors that come off of a catalyzing mixture.  I had one of their employees tell me that I just “shouldn’t huff the vapors.”  Another employee told me that it’s “really not that bad.”  While another employee told me that “all resin is dangerous” and I should “take the necessary precautions to protect myself from inhalation of vapors.”  The web page, along with most of the employees have told me that it is alright to use the product in doors, but it needs to be a used in a well-ventilated area.  Others have suggested that a “room-sized” ventilated area is fine.  I’ve been warned not to do it in my closet or small bathroom.  (Ok. Thanks.)

Now, I found this one article online at which I admit is kind of a random blog, (but wikipedia confirms some of this information about polyurethanes isocyanates (an organic/carbon compound)  being dangerous to one’s health. ( ).  The effects of inhalation listed in this article include lung irritation, asthma attacks, difficulty breathing, causing lung infections, and brain swelling (in a bad way.)  Also prolonged exposure for workers can health disorders such as unsettled stomach, vomiting, and dizziness. 

So what’s the truth about polyurethane resin?  Well, it’s dangerous.  Just read the rest of the Safety Sheet again ( .)  Notice the repeated warnings about Part A: “Harmful if inhaled;” “May cause allergy or asthma symptoms or breathing difficulties if inhaled;” “May cause respiratory irritation;” “May cause damage to organs (Olfactory organs)) through prolonged or repeated exposure (inhalation).”  Part B: “Fatal if inhaled;” (which sounds bad).

In conclusion, I’m not trying to be overly dramatic.  I’m just worried that their are young people out there that read all of this communities’ posts and get really excited to get involved, but never stop to consider what it is they are getting involved in.  I mean it is a ton of information and none of it is straightforward, so I'm just trying to help some find the relevant information.  The thing is driving a car is dangerous, but when you put on your seatbelt, only drive when well rested, follow traffic laws, etc. you reduce the risk of being in a fatal accident.  Anything can still happen, but what kind of life is it if you just sit around in your house and never take any risks.  If you’re reading this you are probably passionate about resin casting, so I wouldn’t ever try to stop you from pursuing that.  (I don’t plan to stop either.)  However, just take the necessary precautions to protect yourself, such as wearing a respirator (note that only respirators that protect from ORGANIC VAPORS will do you any good), using a fan to waft vapors out of your face, and use in a well-ventilated area.  It’s really not that big of a deal.  Take care of yourself, so you don’t die before we see your cool caps.  Cheers.
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Offline klaushouse

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Re: Resin Casting and Harmful Vapors
« Reply #1 on: Sat, 12 August 2017, 15:07:18 »
Thanks for the awesome info, I'd rather live longer to be able to use more urethane. Although sometimes when I'm out of the devil's grass it helps tide things over with a little whiff of the ole' Urethane Part B. ;)

Offline kurplop

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Re: Resin Casting and Harmful Vapors
« Reply #2 on: Sat, 12 August 2017, 17:57:58 »
What further complicates the issue is the ubiquity of warnings on almost everything. There are certainly dangerous chemical compounds out there and many deserve our respect. Unfortunately the truly deserved warning labels get minimized by the unwarranted ones.

I would never tell someone to ignore the warnings but experience tells me that many, perhaps most, of the warnings are excessive. This has resulted in either a "boy that cried wolf" mentality where all warnings are ignored, or, maybe worse, a public fear of doing anything without nitrile gloves, respirator, and protective eyewear.

Common sense and reasonable precaution should always prevail.

Offline sinusoid

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Re: Resin Casting and Harmful Vapors
« Reply #3 on: Wed, 16 August 2017, 05:35:26 »
Polyurethanes are a cured mix of polyol and isocyanate. Isocyanate is the one that's volatile. It is reactive with water, and easily mixes with it. For this reason, you DON'T get it on your skin, ever.

Isocyanates cause sensitization. So you get exposed for a long time, and nothing happens. When you get sensitized, you will have asthma-like symptoms of various severity whenever you get exposed to isocynates or badly cured polyurethanes. This can kill you, but most probably won't. Not on the first try, anyway.
I've also read somewhere that isocyanates are a suspected carcinogen, but I don't know how recent that was, and whether it was proven/disproved.

Polyurethane resin formulas that were developed recently contain isocyanates that have a fuming point of around 38 degrees celsius. It should be in the spec sheet. Always ask for the spec sheet. Below that temperture they are considered safe to work with. However, some fumes will accumulate in the container and escape when you open it.

The densities of isocyanates in the air are dangerous long before you can smell them. The car service guys use external air delivery systems + ventilation, or change the active carbon filters every day. For small volume stuff a fume hood should work well.

I've read that carbon filters can saturate over time with isocyanate, and when that happens your lungs will get all the isocyanate from the air, and a bonus that starts to emit from the carbon filter, which is not exactly the cheapest.

- get a fume hood
- store the resin in a ventilated area
- use modern resins whose isocyanate has a high fuming point. Look to lcamtuf's guerilla guide to cnc to find them (just search for this phrase and go to casting section).
- spray the containers of the resin with a heavier gas to keep the air out once in a while, and before closing them for storage. I use propane. I didn't verify if it's a good idea (reactivity), but empirical data shows no degradation of resin over time. I will use N2 instead when I'll figure it out.
- OBEY THE MIXING PROPORTIONS. If you get that wrong, some of the isocyanate will not react with the polyol, get trapped in the mix... I hope you see where this is heading :|
- cure in a ventilated area, they will fume while curing
- if you can smell the isocyanate in the air, get out and ventilate, and make sure you identify why this happened to avoid it in the future.
- whenever you put PU into vac chamber, assume it's full of isocyanate vapour when you open it.

That's what I do. When I'm not sloppy, and not in a hurry... it really sucks being susceptible to the human weaknesses some times -_- (i tend to cut back on temporal safety sometimes, but never on permanent - so, may decide on weaker ventilation, or none at all, but NEVER mix sloppily, or let resin react/degrade or store improperly)

On the brighter note, most of that stuff goes for people who get a continuous exposure to isocyanate mist, for example in car body preservation, where you spray a few liters of that stuff on a metal frame at high pressure. I guess it would make them mostly safe to work with if you have a bit of common sense.
Some polyurethanes have amazing mechanical and chemical properties. Read up on that in your spare time, lcamtuf's guide is a nice start. The smooth-on stuff doesn't even scratch the surface of awesome.

edits 1, 2: fixed ambiguity and style

edit 3:
I just remembered some older polyurethane formulations, still in use today, use mercury or lead compounds as reaction catalysts between the polyol and isocyanate. Make sure you're not using one of these. They may sometimes NOT be labelled properly, so make sure you get full resin specification sheet prior to purchase, or with it. You ARE able to buy them without being straightforwardly told you're buying toxic chemicals, a lot of companies sell these assuming the recipient knows what they're doing, and have proper tools and procedures in place.
« Last Edit: Wed, 16 August 2017, 17:25:51 by sinusoid »

Offline I_am_not_me_

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  • Location: US California
Re: Resin Casting and Harmful Vapors
« Reply #4 on: Wed, 16 August 2017, 15:16:00 »
As someone new to making artisans, I really appreciate this being said. I recently heard this from a friend and was wondering why I don't see it more often.

Offline CompileWithStyle

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Re: Resin Casting and Harmful Vapors
« Reply #5 on: Sat, 19 August 2017, 19:04:59 »
The scary thing about gases is you can't see or smell most of them as they are odorless.  Even if you are smelling an odor it may not be the gas/fume given off.  When working with any materials involving chemistry you MUST practice the safety precautions.

If the material is even the slightest bit dangerous slap on your glasses, gloves, and respirator if needed before getting down to business.  Hope for the best but always plan for the worst.  It's the makers way  :cool:

Awesome post sinusoid!!! TY
« Last Edit: Sat, 19 August 2017, 19:06:41 by CompileWithStyle »
CompileWithStyle - Some of my work

Offline sinusoid

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Re: Resin Casting and Harmful Vapors
« Reply #6 on: Thu, 21 September 2017, 03:10:51 »

Here, read these two MSDS (material safety data sheets). They are for both parts of a fast-bonding prototype resin. This is generally what you'll be looking for when working with unknown chemicals. Both list health concerns, and specific substances responsible for the dangers. These are recent resins made by Axson (now part of Sika I think), afair they appeared in their catalog in 2015.

i should attach them... the links are gonna get broken sooner or later... I know I should... aaahhhhhh

Offline Findecanor

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Re: Resin Casting and Harmful Vapors
« Reply #7 on: Thu, 21 September 2017, 11:20:20 »
Different brands of urethane resins can contain different types of solvents. I used to use one from Esprit Composites which ate through my plastic cups in no time where as others who used similar resins from Smooth-on never had that problem.

More worryingly though... Scientists have found a possible link between isocyanites in urethane resin and electro-hypersensitivity. The theory is that isocyanates is the real cause - and electric fields is only the trigger for the symptoms.

Offline KeLorean

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Re: Resin Casting and Harmful Vapors
« Reply #8 on: Thu, 21 September 2017, 13:15:59 »
kinda went dark on this for a while, but man, great info everyone.  thanks for your contributions.  i thought i was doing pretty good with my safety but now i realize that i have had a few "bad" practices, such as not wearing my respirator when i release my pressure pot, touching poorly cured/tacky resin with my bare hands, and reusing a piece of cardboard as a "drop mat" which has been doused in uncure and cured resin which i inadvertently touch later while working on that surface without gloves. i intend to correct all of these shortcomings and do my due diligence to avoid poisoning myself
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Offline rachel

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Re: Resin Casting and Harmful Vapors
« Reply #9 on: Thu, 18 October 2018, 14:53:09 »
I have been reading a lot about resin due to concerns I have with its safety.
I guess it's really important to remind makers/new makers of its safety handling.
Here is an article I would like to share

My takeaway from my research is this, first line of defence is to have proper ventilation in the resin workstation, then followed by respirator with carbon filter cartridges. Exposed skins to be covered.

Safety first peeps!
« Last Edit: Thu, 18 October 2018, 14:54:54 by rachel »

Offline pastuh

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Re: Resin Casting and Harmful Vapors
« Reply #10 on: Sat, 24 November 2018, 09:10:50 »
Thanks. Useful information