Epoxy resin cure time?

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Epoxy resin cure time?

Postby SMHolmans on Mon Oct 22, 2018 7:37 am

Hi all. I'm having trouble getting my resin to harden. The last coat is now nearly four days old and it's still very slightly tacky. It's not that cold (18 to 19 C) and it's not humid in my workshop (55 to 65%). Any suggestions on what I might be doing wrong, or am I being impatient? Thanks!
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Re: Epoxy resin cure time?

Postby ddemasie on Mon Oct 22, 2018 11:36 am

Ouch. 18 - 19C seems like enough warmth. Epoxy uses a chemical reaction to harden, the reaction generates heat itself, but cold conditions tend to slow it down too much. I never mixed epoxy if the ambient temp was under about 55 degrees F - But 60 - 65 degrees F was always enough in my experience.

Double check your mix. Any time I had problems with the mix hardening it was due to not mixing enough hardener in with the resin(the 2:1 ratio needs to be pretty exact for proper hardening).

I'd maybe check with directly with MAS - or whoever you got the epoxy from.
Dennis DeMasie,
Aurora, IL
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Re: Epoxy resin cure time?

Postby riverron on Mon Oct 22, 2018 1:19 pm

I agree with Dennis, the epoxy should cure in 60 + degree temps, however I do recall some of mine being tacky for up to a week when I applied some during the winter months. I used a work light to help with curing when it was cold. It definitely needs to be cured before sanding.

For the 18-19C, is your work space staying that constant temperature? or is that when you are applying during the day and the temperatures in the workspace is dropping during the night? The work light should help with that.

What type of epoxy are you using?

thanks
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Re: Epoxy resin cure time?

Postby SMHolmans on Mon Oct 22, 2018 1:42 pm

Thanks Ron and Dennis. I am seriously wondering if I am doing something wrong here. The coldest my workshop has been overnight since I started work is 14 C. That doesn't seem very cold to me - not in the UK in October. Is mixing an issue? About how long do you guys mix your mixture before use?
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Re: Epoxy resin cure time?

Postby John in CC on Mon Oct 22, 2018 1:50 pm

Be sure to stir a lot!
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Re: Epoxy resin cure time?

Postby SMHolmans on Mon Oct 22, 2018 1:55 pm

Can you suggest stirring times e.g. 1 minute or 20 minutes?
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Re: Epoxy resin cure time?

Postby TassiePete on Mon Oct 22, 2018 3:06 pm

Hi,

Sorry to hear about your epoxy issues. Epoxy curing (and working) time is very much depended on temperature. I am using the West System epoxy (mixing ration 5:1) and it works fine down to 5 C. It will certainly cure within 24 hours below 10 C. Above 25 C you have to be very fast, or your batch will heat up and go off in a few minutes. In hot weather thin coats will set within in 6 hours.

To prepare any mixes, I always used kitchen scales. I take x numbers of grams of hardener in a plastic cup, and top it up to (x * 6) g of mix (e.g. 5 g hardener + amount of resin to make 30 g). This method works very well, because any small error is with the larger quantity, and the ratio will be acceptable give or take a couple of grams.

I usually mix for about 30 secs if it is warm (resin and/or weather), longer (1 minute ?) if it is cold. The stuff gets very syrupy below 10 C.

Peter
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Re: Epoxy resin cure time?

Postby riverron on Mon Oct 22, 2018 3:10 pm

I am using MAS epoxy with slow hardener. I typically mix 3 minutes for just about everything. I have a clock on my wall with a second hand.

With 14 C at night, I would use some type of work light to warm the area.
You can see the table below that Temp 50 is NOT recommended and you are getting close.

You can also see using Slow Hardener, it can take up to 7 to 10 days for full cure, so your 4 - 5 doesn't sound out of the ordinary.


Temp 2:1 Resin/Slow 2:1 Resin/Medium

Pot Life / Thin Film Set / Full Cure

95 11.5m/2:30h/2.5d 6.5m/1:30h/42.0m
86 17.25m/3:45h/3.75d 9.75m/2:25h/63.0h
77 23.0m/5.0h/5.0d 13.0m/3.0h/3.5d
68 34.5m/7.5h/7.5d 19.5m/4.5h/5.25d
59 46.0m/10.0h/10.0d 26.0m/6.0h/7.0d
50 69.0m/15.0h/15.0d* 39.0m/9.0h/10.5d
41 92.0m/20.0h/20.0d* 52.0m/12.0h/14.0d
* Not recommended
s = seconds; m = minutes; h = hours; d = days
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Re: Epoxy resin cure time?

Postby jwv630 on Mon Oct 22, 2018 5:58 pm

Hey Guys

I spoke with a technical guy at CLC a few weeks ago about epoxy. He said they are now recommending a minimum temperature of 65 degrees for epoxy applications that are for structural work; minimum temp for non-structural is 60 degrees. I stir my epoxies for a few minutes. Could it be amine blush that you're feeling and not the epoxy itself...? I want to continue working thru the winter in an unheated garage but really not sure this is feasible (I live in Baltimore), even with work lamps and plastic tenting.

Jimmy V
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Re: Epoxy resin cure time?

Postby JonLee on Mon Oct 22, 2018 6:47 pm

My first suspicion is that you are not getting the right ratio of hardener-to-resin, in which case it will never harden. Epoxy resins harden require the ratio of resin and hardener to be fairly precise to cure properly. They must also be thoroughly mixed.

To test out this theory, you can mix up a small batch of epoxy (3-4 pumps) in a mixing cup and bring it inside the house to cure; this will remove the temperature part of the concern. Unless you live in an unheated castle. You can either leave it in the cup and apply some to a piece of spare plywood.

I have run into similar problems before. I will not admit to anything, but it is possible that in some cases the problem was working at too low of a temperature, in which case time and applying some heat eventually did the trick (don't ask about what is did for the strength of the bond, because answering that might cause me to admit to something). In some cases, and again I'm not admitting to anything, I might not have mixed my epoxy right. I won't say what I might have done to fix it, because I'm 93.6% certain that what I might or might not have done was not a good idea.
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