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Epoxy too fast!

PaulMB

PaulMB

pfm Member
I realise it is a minor problem in the context of human existence, but here in Italy it is becoming virtually impossible to buy a normal 2-part epoxy adhesive that gives you more than 5 minutes usability. Which makes it difficult to assemble and maybe carefully clamp something a bit complex or large.

Some will remember that the original Araldite took hours to go hard, and at least 24 to reach full strength, which could be tiresome.

But today it seems to be the opposite problem. I know "standard" Araldite still exists, at least in the UK and Switzerland. But in normal DIY shops (at least in Italy) there is no Bostik or UHU or Pattex equivalent that does not go stone hard in 5 minutes. There used to be, but no longer.

I've tried halving the amount of hardener, which takes it from 5 minutes to maybe 7 or 8. But will it be as strong? And why this mania for all-out speed?
 
get a nice person here to pop some in the post for you?
I did see an ad for some glue which sets under UV light....you do all the clamping first then when ready, do the UV bit I think. Lots of time in prep then no waiting?
 
Rockmeister said:
get a nice person here to pop some in the post for you?
I did see an ad for some glue which sets under UV light....you do all the clamping first then when ready, do the UV bit I think. Lots of time in prep then no waiting?
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Not worth the trouble. I can order it from the UK. But I was wondering if anyone else was puzzled by this
The UV system is also used by dentists, they fill a tooth and when all is nice and smooth they shine a concentrated UV ray on it.
 
UV cure is of little use if using in a join that is any depth/width/distance from an edge where it can be hit by the UV.

For most uses, I would bet that there is something far more appropriate to use than an epoxy, and with a longer open/cure time.
 
Do you live near the sea? A marine store should sell standard epoxy resin for fibreglass repairs.

I think epoxy is a two part formula so I wouldn't adjust the ratio. It can be retarded by cooling.

Polyester resin is activated by a catalyst so you can control the speed of reaction, but the fumes are more toxic than epoxy so I highly recommend a respirator and goggles if you're going to use it.
 
I suspect it is temperature dependent too. Probably a lot quicker in Italian summer temps. Plenty of working time here in the UK...
 
I use urethane glue or caulking whenever I can because of the too fast curing time of epoxy. Not as strong but quite enough for many applications.
 
Thank you all for the many interesting suggestions. And yes, certainly the 36 degrees we have now do not help.

But the thrust of the thread was that I'm baffled why in mainstream shops only 5 minute epoxy is available. A couple of years ago I could still find, with some difficulty, a 90 minute version. But now it is all 5 minute. Do not understand why.
 
matt j said:
Can you not mix it with less of the hardener to give you more time?
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No. The reaction is the epoxy-amine one:

images


It relies on the very strained epoxide group (the triangular thing with the O) which is busting to react with nearly anything to relieve the strain. Amine (NH2) is particularly effective. So you need one epoxy for one amine, thus 50:50. Reduce the hardener and you will have a lot of unreacted epoxy. This is why the stuff is two-pack - you daren't let the two bits near each other until you're ready to use them. I think you might be thinking of the reaction used to make fibreglass - that is unsaturated polyester in styrene, and it's a free-radical reaction, triggered by a relatively small amount of initiator.
 
PaulMB said:
Thank you all for the many interesting suggestions. And yes, certainly the 36 degrees we have now do not help.

But the thrust of the thread was that I'm baffled why in mainstream shops only 5 minute epoxy is available. A couple of years ago I could still find, with some difficulty, a 90 minute version. But now it is all 5 minute. Do not understand why.
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Customer demand, I suspect. Not many folk have the patience for the standard article (half an hour workability, 12 hours to initial set, 3 days to complete set). You can speed the whole thing up by choosing a hardener other than amine - one possibility is mercaptan (where the OH of alcohol is replaced by SH - and yes, it does indeed smell like it - ethyl mercaptan, the sulphur equivalent of ethyl alcohol, is a contender for the worst-smelling substance in all creation). Specialist mercaptans are used in those double-syringe fast-setting epoxy adhesives, where the quantity is sufficiently small not to need a gas mask.
 
Sue Pertwee-Tyr said:
I suspect it is temperature dependent too. Probably a lot quicker in Italian summer temps. Plenty of working time here in the UK...
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Yes, cure time is roughly halved for every additional 10C. I cure 24hr Araldite and laminating epoxies in an oven at 50C and get a full cure in 3 hrs.

CHE
 
tones said:
Customer demand, I suspect. Not many folk have the patience for the standard article (half an hour workability, 12 hours to initial set, 3 days to complete set). You can speed the whole thing up by choosing a hardener other than amine - one possibility is mercaptan (where the OH of alcohol is replaced by SH - and yes, it does indeed smell like it - ethyl mercaptan, the sulphur equivalent of ethyl alcohol, is a contender for the worst-smelling substance in all creation). Specialist mercaptans are used in those double-syringe fast-setting epoxy adhesives, where the quantity is sufficiently small not to need a gas mask.
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Thanks Tones, all very clear. Do you think the slow version works better than the super-fast versions? There is an in-between UHU version that is hard in 90 minutes and full strength in 12 hours, which I used for years and seemed fine, and the standard Araldite, which I seem to remember you could work with for about 90 minutes, was hard in 8 - 12 hours and full strength in 24 (I think?). They were both fine, fantastically strong. But the newer super-fast types seem not quite as good. Would your chemical vision support this feeling, or is it all in my mind?
 
PaulMB said:
Thanks Tones, all very clear. Do you think the slow version works better than the super-fast versions? There is an in-between UHU version that is hard in 90 minutes and full strength in 12 hours, which I used for years and seemed fine, and the standard Araldite, which I seem to remember you could work with for about 90 minutes, was hard in 8 - 12 hours and full strength in 24 (I think?). They were both fine, fantastically strong. But the newer super-fast types seem not quite as good. Would your chemical vision support this feeling, or is it all in my mind?
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Hello, Paul, to the best of my knowledge, the fast-curing epoxy adhesives aren't as strong as the normal-rate curing ones, but, depending on the application, this may not matter.
 
PaulMB said:
Thanks Tones, all very clear. Do you think the slow version works better than the super-fast versions? There is an in-between UHU version that is hard in 90 minutes and full strength in 12 hours, which I used for years and seemed fine, and the standard Araldite, which I seem to remember you could work with for about 90 minutes, was hard in 8 - 12 hours and full strength in 24 (I think?). They were both fine, fantastically strong. But the newer super-fast types seem not quite as good. Would your chemical vision support this feeling, or is it all in my mind?
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I only use the slow cure Araldite as besides being stronger than the rapid cure stuff it will flow by a small amount which is a good thing for certain jobs and usually gives a neater appearance. As CHE says, heat will reduce the curing time. I only have a halogen lamp but it does help speed up the setting time when required. Patience is a virtue of course in most situations :)
 
That was my impression, that the slow epoxies, be they Araldite or UHU Plus, are simply better to work with. They are dense and semi-solid when mixed, then become more liquid before setting, so they "settle" and fill up small spaces. In fact I've found that if you set the glued object in the right direction, you can use gravity to make it set as you like.
 
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