Epoxy

[Keith Evans 3]

I've been using two pack epoxy ,with great success , since they first came on the market many moons ago.However very ,very occasionally it fails to set rock hard and ends up more like a very hard rubber .I am very careful measuring the amounts of hardener and resin and mix them really well .

This problem can happen in the same batch .Some results are good and one may not be .

This problem has only raised its head , say only 3 or 4 times in all the times I have been using it .

I'm about to use some epoxy soon in a very critical part of a build . As it is in a very difficult place to reach I dread the thought of ending up with "rubber" .

Any advice would be welcome .

Happy new year .

Keith

[Martin Harris - Moderator]

Ambient temperature?

[Nigel R]

Humidity?

Contaminants getting in to the mix somehow?

[Cuban8]

I can't give a definitive answer as to the 'rubbery epoxy' problem, caused presumably by the two components not chemically reacting correctly or fully together. - it's only happened to me on one occasion and that was with Araldite a very long time ago. If the material is mixed correctly then I suppose the only things to check for are possible contamination (unlikely) or maybe the particular brand that's being used has a shelf life that's been exceeded. I have a feeling that's what happened with my soggy Araldite.. Possibly poor storage in a humid environment without proper sealing of the containers? Very odd that Keith says he's had a problem from the same batch - some good some not.

My advice would be to use a new fresh 'modelling grade' epoxy (I've been using Bob Smith products with no problems for ages) and mix up a trial amount at room temperature and see how it goes. Mixing up quite large amounts in a pot will require careful and thorough mixing to avoid incomplete combination of the components. Less likely with a small dab mixed on an old credit card?

Edited By Cuban8 on 01/01/2020 12:10:40

[Don Fry]

I would (tin had on) say that is a mix ratio problem. Cause is trying to use just enough for the job, because it's expensive, and then the ratios drift because of the tiny amounts used, and an inability to get the half mixed stuff off the mixing stick.

Humidly has some effect, and it should be cured at a comfortable room temperature. But if you are comfortable working in the room, that's fine for the resin as well.

I don't use epoxy glues as much as I used to. I find the brown expanded polyurethane Gorilla glue is easy to use, and very strong. But for some jobs an expanding glue is not appropriate.

[Allan Bennett]

I've experienced a 'rubbery' result from time to time, and put it down to incorrect proportions when mixing from two separate tubes. Of late I've been using the type that's in two connected tubes with a single plunger, and seem to be getting more-consistent results.

In winter one problem, in my unheated workshop, is it's sometimes too stiff to come out of the tube, which can contribute to incorrect quantities being used. A quick blast on the tubes with a hot-air gun has the contents flowing nicely in no time.

[J D 8]

Another fan of Bob Smith products, good stuff and less smell than other epoxy's

[Joe Beavis]

I have encountered the 'rubbery' mix problem with Rapid Araldite - that performed perfectly before and also later. I also put it down to a mixing error. There can be a temptation to mix too small a quantitiy to minimise waste. Sometimes at the beginning of a 'squeeze', a bubble can upset the judgement of quantity, and if the mix is small. this can be critical. If the the tubes are stored in the same attitude (caps up) at no less than normal room temperature, and you don't attempt to mix less than, say a 15mm 'stripe' of each jollop, mix REALLY well, success should reward your efforts. Martin is right, don't push your luck regarding temperature while curing.

[buster prop]

I’ve had mixed (no pun) results with epoxy. I have some Z-Poxy 15 minute which is quite old. Contents of the epoxy bottle had gone almost solid, I warmed it on a radiator which helped but when I mixed it with hardener and applied it to a job it never set properly. Even after 24 hours it was almost but not quite set, rubbery even. I was easily able to pull the joint apart so fixed it again with some ‘151’ 2 part epoxy from a discount shop. That worked but what a pong! I’m back to proper Araldite from Wickes which doesn’t smell and sets properly. The Z-Poxy is probably useless now although it cost me £13..

[i12fly]

OK, not quite the same, but with Araldite I've found it go rubbery if mixing with a bit too much hardener. I always use a bit less hardener than resin now in the mix, not noticed any problem with curing time but it has always set hard, even with glue that is several years old

[Michael Barclay]

Pound shop. I use tons of the stuff. Never had a problem.

Many years experience working with epoxies in the marine industry shows cure problems always down to incorrect mixing, either of quantity or stiring.

[Ray Wood 4]

I will second that Poundland Epoxy & Cyano are great, all I ever use these days!!

Regards Ray

[Bruce Collinson]

Funny how different glues grab different modellers. I tend to work on the basis that with several hundred pounds in the air, I try to pay attention to weak links and, e.g. epoxy joining wings together is one such link. Ditto for tail surfaces, motor boxes et al.

Pacer does have a finite life after which it turns cloudy but it’s my default epoxy.

Mixing; several years ago I bought expensive digital scales direct from the US, for use in reloading rifle ammunition. I always weigh epoxy or any two part substance. It takes all the guesswork and a lot of the wastage out of mixing. I believe they are now available for a tenth of what I paid, although mine owe me not a penny. They may be mass produced copying the original Western technology of a small strain gauge and a circuit board, but if the £10 kitchen scales I bought for weighing models and components accurately are anything to go by, the omnipresent respecters of patents and copyright have succeeded once again.

My expensive ones came with three reference check weights for calibration which are probably now also knocked off in the Far East. My scales rarely need calibrating but I did check the kitchen scales, which are pretty accurate and thinking about it probably use the same technology.

Never had a bad mix yet. I used some Araldite for knife scales but didn’t see any gain compared with Pacer.

And finally, wasn’t there an excellent article or two in the mag by the proprietor of Deluxe Materials about a year ago? I remember one thing from it, he said that there’s about 10% leeway before epoxy won’t cure properly.

BTC