Hi guys, I just tried to do a resin infusion (doing it as a hobby, glassing wings for model aircraft) in the garage and the resin just didn't want to play ball. After 5 hours of using a heat gun to get the resin to flow into all the spaces on the wing (doubly hard to do the top and bottom of the wing at the same time) and the damn stuff just wouldn't shift, what's the minimum working temperature for this stuff. It's been a cold night, started at 4 deg and it went down to -1 deg. I know the pot life is 40-60 mins, I guess I stuck with it out of desperation as the wing alone took 38 hours to shape . Any input would be great, thanks guys.

Hi and welcome CJ.

Temperature: It is vital that the temperature of the working environment is correct, all curing times stated for our epoxy systems are set at a working temperature of 20ºC during the winter it is very easy to work in an environment that is too cold, this will lead to very slow curing rates and can expose the uncured epoxy to moisture from the air which can result in the resin never fully curing. Also the viscosity at lower temperatures increases hugely, this can mean poor ‘wet-out’ of the fibre or if doing resin infusion; very slow flow rates. An absolute minimum working temperature should be no lower than 15ºC, even at this temperature expect curing time to be dramatically longer than specified. If temperatures run over 20ºC which can sometimes be unavoidable especially in the summer months, expect the reverse effect; viscosity of the uncured resin will reduce, which can lead to excessive draining on wet lay-ups, gelcoat, filler, etc. Cure times will also shorten greatly with increasing temperature, this will leave you with less working time and the increased likelihood of exotherm.

It sounds to me like you are working in an environment which is far too cold, I would suggest running the acctual infusion in a warmer place so find somewhere at 15deg C+ leave the resin (before mixing) and the mould there for a few hours to allow them to raise up to temperature and you should get much much better results, Using a heat gun to temporaraily heat the resin to lower the viscosity is not really the best idea, it's very easy to over do it and start the resin curing.

A trick that we have used in the past in cold workshops is to wrap the mould in an electric heated blanket (one that you would put on your bed) and cover it in an insulated jacket this can be used to get the mould to 20deg C, it's also important to store the resin somwhere warm before use.

You will find that the resin will not really be curing on the part at those temps, although it may do in the pot where it has a bulk mass to warm itself through exotherm. So it might not be too late to mix a new batch of resin, get it somewhere warm and hope it still has some life in it, let us know how you get on there's nothing worse than watching hard work get ruined, we've all been there at some point. 

Paul Statham
Easy Composites / Carbon Mods - Technical