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Epoxy glue - gone off?


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I have some Zap 30 minute epoxy which I bought last year and have only used a small amount so far. Went to use it the other day and saw that the resin has slightly crystallised / solidified as can be seen in this photo. My question is, can I still use it if I can make it work workable by the addition of heat? I use heat in the winter to make epoxy more 'user friendly' but this isn't quite winter!

IMG_6051D.thumb.JPG.a21b19250ae34d5310158023ab4f56ad.JPG

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Hi Ron

The resin has probably partly polymerised , it shouldn’t cause a problem but it might, so try mixing some with hardener and see if it goes off properly .Heating the resin could cause further reactions .You can thin epoxy with ethanol or methanol but don’t use cellulose thinner 

Alan

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Put the bottle in the microwave for 10 seconds at a time (without the cap) until the crystals disappear. Let it cool down before using otherwise you will speed up the setting time. This crystallisation is quite normal and in industrial situations ( shipbuilding etc.) it is normal to have large hot water baths capable of heating up 40 gallon drums of resin. The properties of the resin are not altered or harmed.

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Yep, have seen this quite often with ZAP 30 minute epoxy, especially if it's been stored in the cold. In my previous workshop it was a pre-requirement to stand the epoxy bottles in a tub of warm water to bring them up to a temperature where they would be able to flow.

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I have microwaved the same solidified Zap epoxy multiple times with no ill effects in performance however - 5-10 sec MAX bursts with as others have said with the tops off as it heats up really quickly or it will cost you a new microwave? 

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I have to say that I didn’t expect to have to warm the resin up in the summer! In the winter I put both resin and hardener bottles on the oil filled rad in the workshop until they both flow, then use them. Rather that a hot water bath I suppose I could use my heat gun.

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  • 2 months later...

I still use this Araldite without problems. Initially I thought it was old, but it can't be, given that the price on the box is in decimal currency...  I think it dates from the about 1973.1507054567_OldAraldite.thumb.jpg.cccd5b1315eb4c03a2b6a9780ac0d892.jpg

Warming the components to be bonded to a higher temperature than the mixed epoxy reduces its viscosity at the bond face, stops the workpiece chilling the epoxy, and also reduces the likelihood of air trapped at the bond face.

Its always worth doing a post-cure with epoxy. Whatever temperature it is cured at determines the glass transition temperature at which it goes soft again.
Put the component in the warmest possible place after the initial cure. Full-size sailplanes are put in hot boxes at 70°C+ for 12 hours or more after a repair, otherwise they could exceed the glass transition temperature in a trailer on a hot day resulting in permanent distortion.

Edited by Robin Colbourne
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