Epoxy not set !!!!!

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slipknot

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The boats on the hard and I did a very small repair to the fairing of my keel using West System 105 205 & 407 filler. It was pretty cold and I did apply some heat, but it seems not enough. It has hardened but I don't think fully. I'm concerned that when I relaunch it might just wash away. Am I too late to apply more heat to it to get it to go off, or do I start again?
 
Start again and till it's warmer. A quick burst of heat isn't enough it needs to be at a moderate temp for the duration of the cure.

How did you measure it out? The ratios have to be pretty precise. Of needs be it's also better to err with a bit too much hardener than a bit too little.
 
West system are fairly clear in their instructions that you should use the correct amount of hardener, direct quote from website.
DO NOT attempt to adjust the epoxy cure time by altering the mix ratio. An accurate ratio is essential for a proper cure and full development of physical properties.
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I had a quick look on the West website, and with 205 hardener, you should be good down to 4 degrees, but it will take longer to cure fully.
I'd give it a few days and see if its still too soft, if so, remove and do again.
 
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If there is insufficient hardner, the epoxy will not cure properly. If insufficient hardner is used, it will all be used up before the epoxy has set off. So if only 80% of hardner is added, the reaction will stop at 80% and can go no further. In practice the last traces of hardner will continue to react allowing a further degree of hardening, but if there is not enough, it will never fully cure the epoxy If there is too much it dilutes the mix and weakns it. Temperature is important too, as the reaction will not continue between the two chemicals. If this occurs, the reaction cannot restart when it is warmed up again. The end result is the same - soft epoxy! The only cure is to remove it and to start again.
 
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prv said:
Is there a reason for that?

Pete
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Yes. At a molecular level 5 molecules of resin need to bond to 1 molecule of hardener in order to set. So any shortfall in harder will leave five times that quantity of resin uncured in the mix. Where as a small excess of hardener will only leave that small quantity unset.

Of course better yet to get the mix as spot on as possible, but if you get in a muddle and think you've put too little harder in then a spot more won't hurt unless it's a really really small batch.

Their warning about proper mix ratios is to stop idiots putting twice the hardener in thinking it will cure twice as fast. These are usually people who know about fibreglass and polyester resins but are new to epoxy and assume it's the same thing.
 
slipknot said:
The boats on the hard and I did a very small repair to the fairing of my keel using West System 105 205 & 407 filler. It was pretty cold and I did apply some heat, but it seems not enough. It has hardened but I don't think fully. I'm concerned that when I relaunch it might just wash away. Am I too late to apply more heat to it to get it to go off, or do I start again?
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No you arent too late. Its a chemical reaction and like all such reactions its temperature dependant. All its done is either slow down or stop reacting. Borrow your wifes hair dryer and play that on the epoxy taking care not to overheat it.
 
prv said:
Is there a reason for that?

Pete
Click to expand...

I imagine that you need a minimum amount of hardener to initiate polymerisation and crosslinking to change from a liquid and "set". I think the hardener is likely to provide carboxyl or anhydride groups required to "join" the shorter molecules together. So insufficient hardener would leave sticky poorly set mess. Extra would set fully if conditions are correct and I imagine that a small excess would be better than a shortage. A large excess would also be bad but the mixture should be more tolerant to excess hardener than a shortage.

I haven't worked as a chemist for about 30 years and also worked in a different area. Perhaps someone has more recent and relevant knowledge.

I'd have thought OPs epoxy might still go off if he can raise the temperature (fan heater?) for a reasonable time. That's assuming it was mixed well, had sufficient hardener and temp. can be raised for a reasonable length of time.

EDIT: Mustn't start typing and then go to boil kettle before completing the post. Several others quicker at typing :D
 
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slipknot said:
The boats on the hard and I did a very small repair to the fairing of my keel using West System 105 205 & 407 filler. It was pretty cold and I did apply some heat, but it seems not enough. It has hardened but I don't think fully. I'm concerned that when I relaunch it might just wash away. Am I too late to apply more heat to it to get it to go off, or do I start again?
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The problem with very small amounts is that the measuring becomes more critical. I did a day course on West Epoxy, and the main message was -there is only one mix ratio, and we do not mean roughly; we mean exactly. If you are not sure, I would start again, but it doesn't work below whatever temp-read the instructions!
 
I have to say I have done some pretty approximate mixes, and on one batch got the ratio completely wrong. It wasn't a critical place, so I expected to have to clean it all off, and start again. Surprisingly it set, apparently as hard as normal, and is still hanging on.
For keel repairs I would be a lot more careful though.

Mike
 
FWIW i coated my wooden garage doors in epoxy resin Saturday afternoon, finally cured hard (thumb nail test) yesterday, to be expected of course given air temps and moisture.
 
Woodlouse said:
Their warning about proper mix ratios is to stop idiots putting twice the hardener in thinking it will cure twice as fast. These are usually people who know about fibreglass and polyester resins but are new to epoxy and assume it's the same thing.
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That idiot would be me then.

Too much hardener resulted in bubbling and smoke rising. Frightening! I had to douse the whole job with loads of cold water and it took forever to cool down. The end result was an utter mess; a nasty cross between brown cinder toffee and rock hard lava.

A salutary lesson for me.
 
I have discouraging anecdotal evidence. I once did some epoxy work at near zero temperature. It kind of set after a long period, but the surface remained sticky for ever. I offer no explanation, only the observation. I suppose it's possible that I coincidentally made some other error, but I don't think so. I tried cooking it with gentle heat to no effect.
 
For some reason I have it in my head that temp needs to be at least 15oC otherwise its too gloopy to wet anything properly..
Would be nice if lower temps are fine since it rarely gets that warm here and at that temp the hardener I got will cure in 5 mins.
 
Dougal Tolan said:
For some reason I have it in my head that temp needs to be at least 15oC otherwise its too gloopy to wet anything properly..
Would be nice if lower temps are fine since it rarely gets that warm here and at that temp the hardener I got will cure in 5 mins.
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For the West 105 resin there are several hardeners available with different curing rates, pot life etc and useable temperature ranges. http://www.westsystem.com/ss/hardener-selection-guide/

205 ( fast hardener ) can be used down to 4C

There is a similar range of hardeners for SP 106 resins and no doubt other makes.
 
I would try a hot air gun, or IR heater.
But if it's got damp between mixing and setting, probably best to start again.
 
chinita said:
That idiot would be me then.

Too much hardener resulted in bubbling and smoke rising. Frightening! I had to douse the whole job with loads of cold water and it took forever to cool down. The end result was an utter mess; a nasty cross between brown cinder toffee and rock hard lava.

A salutary lesson for me.
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You can also get the spontaneous combustion if you use the right ratio in too small a pot or at too high an ambient temperature. The reaction generates heat, and heat speeds up the reaction so if the heat can't dissipate fast enough then it just gets hotter and hotter. Which is why wide shallow mixing pots are best and you should never do really big mixes in one batch.

I'm not sure that it will result in actual flames though, I've never seen a batch catch fire at any rate.
 
The reaction is exothermic, generates it's own heat, and the reaction starts as soon as the components are mixed.
Below 4 deg it can be halted, but assuming it was warmer than that it should have cured. In summer conditions, West 205 will be dry in around 4 hours, fully hard in around 10. In the winter you can easily double that, but it will still go hard.
If it still feels soft the next day, dig it out & start again. Pay attention to the ratios, warm the ares with a hair dryer before applying the epoxy, & mix the epoxy in a plastic pot, standing in a bigger pot of hot water about the same temperature as a cup if coffee to keep it warm while you work.
 
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