If epoxy adhesives fail to set within 24 hours, is there any hope that they will EVER do so?

[John Smith 47Participant @johnsmith47]

Hello

If Epoxy adhesives don't set properly within the first 24 hours, is there any hope that they will EVER set?

e.g. Would applying a sustained gentle heat have any hope of working?

Background
I have bonded some stuff with Zap's "30 minute" Z-Poxy. Unfortunately although I measured it quite carefully by eye, and although it has now "set" in that it has become brittle, it is still distinctly sticky to the touch.

Cause
It was a fairly small blob – about the size of a couple of peas – and I mixed it with a cocktail stick for a full 4 5seconds. So I can only assume that I failed to get the proportions correct. It's very surprising because it's the first time in about 5 years that I have failed to get 2-part epoxy resin/adhesives to set.

I was bonding at a slightly low room temperature (c.18C). But maybe Zap's Z-pox requires super-accurate proportions.

The parts in question are quite valuable and almost impossible to replace…. but it's now too late & would be too time-consuming try and scrape everything back to start again. So I fear I shall just have to wait to see if they actually break and then patch them up. Unless applying a sustained heat (e.g. 35 to 60C??) might work…?

J

[John Smith 47Participant @johnsmith47]

[SteviegtrParticipant @steviegtr]

Hi John. I have used many types of epoxy adhesives. I can confirm that they are very temperature sensitive. I did some a month ago & left in the workshop for 2 days. It was still sticky. I took it in the house & left it near a radiator for a day & it cured. Not sure of the shelf life of some of them. I have glass fibre resin that i used 3 years ago to make new panels for a Motorhome. I have just given the leftover to a friend & it cured perfectly. Although with glass fibre resin the activator is 1 to 3% dependant on cure time req & temperature.

Steve.

[BizibilderParticipant @bizibilder]

If it is both Brittle and sticky then the most likely cause is that it was not fully mixed. Otherwise I agree with the above – warm it by placing above a radiator for a day.

[noel shelleyParticipant @noelshelley55608]

Along with the rest, warm it ! Noel.

[SillyOldDufferModerator @sillyoldduffer]

I think the reasons suggested by John are correct: 'mixed it with a cocktail stick for a full 4 5seconds' probably wasn't enough to thoroughly intermix resin and hardener, plus the epoxy was mixed at the cold end of 'room temperature'.

Zap's blurb says 6 to 8 hours to fully harden.

Although heating usually speeds up chemical reactions overdoing it might weaken the bond. If heating the joint was beneficial the manufacturer would probably recommend it. Instead my epoxy instructions all give an upper cure temperature of 30°C.

I'd cross my fingers and leave it for a day or two in a warm room. I think it will harden eventually. How long it takes will depend on how unmixed it was, assuming that was the cause.

Dirt is another possibility. Many adhesives are trashed by traces of oil or grease. My many past failures seem to have been fixed by applying fresh glue to carefully cleaned surfaces with a clean spatula and following the instructions exactly.

Dave

[speelwerkParticipant @speelwerk]

"Not sure of the shelf life of some of them."

Steve, the Araldite AW 106 I have now for 40+ years still works as new. Niko

[duncan webster 1Participant @duncanwebster1]

Modest heat won't cause any problems, in fact it makes it flow better. I often find epoxy is still a bit 'not quite right' after 24 hours, but after another 24 it is usually OK. That is the slow cure stuff, don't use fast cure.

[Pete WhiteParticipant @petewhite15172]

Mixing / proportion problem to my thinking. The contamination issue mentioned also appeals. Do we now what sort of wood the cocktail stick was made from, stainless steel rod would have been by choice in a critical bonding operation?

I won't say more on the thread, I am very busy at the moment, but good luck John

Pete

[HopperParticipant @hopper]

Posted by John Smith 47 on 14/02/2022 15:55:35:…

…

I was bonding at a slightly low room temperature (c.18C). But maybe Zap's Z-pox requires super-accurate proportions….

…Unless applying a sustained heat (e.g. 35 to 60C??) might work…?

 

When all else fails, read the directions, which are readily available online with a simple Google search.

The quoted 30 minute set time and cure time of 24 hours is quoted at 25C.

They tell you specifically that cooler temps mean longer set and cure time.

And they tell you at what temperature you can get it to cure in 35-45 minutes. It is a LOT higher than you are blindly guessing. But you'll have to look it up yourself. Inventors need to develop these skills.

18C? Good grief man, time to start burning the furniture.

 

 

Edited By Hopper on 15/02/2022 07:15:38

[bernard towersParticipant @bernardtowers37738]

Always mix my two packs with flat coffee stirrers until the mix goes milky ensuring a good mix and plus one for applying slightly warm as it flows nicely, just as an aside whether it’s 5 min/30min/2 hr epoxy that is only rough handling time, no epoxies fully cure in less than 24 hours. I used a lot of slow cure epoxy on cylindrical Mazarin parts and after two days it’s a proper machining job, wonderful stuff in the right place.

[TeVeParticipant @teve]

Epoxy reacts with prolonged setting when:

– not mixed thoroughly or in bad proportions. Mix to white or even colour. I often add a small part (less than 3%) of paint (artist oil coolurs) to help securing an even mix.

– to low temperature. Place near heating or rise the temperature in the room.

– addition of an inhibitor of any kind. Start over again.

From my experience, if an inhibitor is mixed in by fault, and if not fully cured within 24 hours, you have to start over again. I have also experience an accelerator mixed in by fault, and it set in seconds during mixing.

[Gary WoodingParticipant @garywooding25363]

Well, did it ever set?

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Gary Wooding on 17/02/2022 07:49:38:

Well, did it ever set?

.

Like ‘tomorrow’ … EVER never comes

MichaelG.

[Danny M2ZParticipant @dannym2z]

Many years ago I had a part time job working for an r/c manufacturer.

When it came to mixing epoxy his mantra was weigh it, then mix it again, and again.

I probably spent five minutes mixing each batch (five minute epoxy was banned from the workshop)

Measure once, measure twice, realise that the thicker blob of part 'B' requires time to spread.

4 -5 seconds mixing is totally inadequate.

At the end of the day I worked out that the faster it sets the weaker the bond and the shorter the life.

* danny *

[DalboyParticipant @dalboy]

Having used epoxy glue for many years I have never encountered it not setting. I am not a fan of the 5 minute setting one. If making pens then I use the 15minute as I am glueing up 5 or more pen blanks onto their respective brass tubes. For some jobs I would like to use 24hr setting but seem to have problems sourcing that, everyone is so impatient now and want things glued immediately

[OldironParticipant @oldiron]

Posted by speelwerk on 14/02/2022 17:22:18:

"Not sure of the shelf life of some of them."

Steve, the Araldite AW 106 I have now for 40+ years still works as new. Niko

A little off topic but my 5kg tin of Devcon must be 15 years old or more. I opened it 2 days ago to repair an item and it was still like new. It has set perfectly.

regards

[Neil WyattModerator @neilwyatt]

The answer is … quite possibly.

Coincidentally, I opened this can of isopon about an hour ago. It seems to have grown a rock hard lump of crystals, produced some brown liquor AND solidified without any aid for the hardener.

I checked the batch dates, 2004. It's only nineteen years old. The can wasn't even rusty!

[Dave SParticipant @daves59043]

Pretty sure Isopon is a polyester rather than an epoxy.

They cure in different ways. The hardener for polyesters is a catalyst that speeds up the reaction – but they do set on their own.

IIRC epoxy is an addition reaction, where both parts are required for the chemical reaction to occur.

Dave

[Peter SansomParticipant @petersansom44767]

I was just talking to an epoxy manufacturer yesterday about temperature and setting time. Using Casting epoxy resin to fill cracks and knot holes on a hardwood bench top. They specify an ideal temperature of 28C.

We are max 19C today min 4C, I was told it will not set when the temperature is below 15C, but when the temperature gets above 15C it will resume setting, I was told just wait or bring it in the house where it is warmer. Did that with the smaller piece, but the other is 4m long so not easy to move.

So just wait and you can apply a bit of gentle warmth.

Peter

[simondavies3Participant @simondavies3]

A couple of thoughts:
I have a pack of epoxy dating from way back purchased from the model aircraft world, and the hardener had crystals forming in it – when I tried to use it, it refused to set. The web suggested that I should heat it gently for the crystals to dissolve back in – this was successful, although I no longer trust the pack!
Also….and our achive specialists can help me here – there was an article some years back (10+?) about engineering adhesives and the instructions for epoxy mixing were to slide a spatula across the mix to combine, rather than stirring. I recall that this was to better combine the two parts – I have taken that advice ever since!

Happy Bastille Day to my fello French residents!

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