Hi Folks,
I am a new member and live in the USA. I have a problem with my resin mixture going off too soon. I bought (medium) speed resin. It is supposed to have about 25-30 min pot life at 80deg. I live in South Carolina, and 80deg is pretty cool this time of year! The temp is expected to get to close to a 100deg this weekend, just as I plan on doing a lamination project. My question is how can I slowdown the reaction of the resin? I will be working outside, so no A/C to help. Would placing the resin in a fridge before mixing help? I know I can't reduce the hardener ratio to slow it down. Any ideas?

Depending on ambient temperature,size of part,using the right harderner,use a harderner which gives you 2 hours     Working time remember when mixed in larger pots it can exotherm.

Hi Gary,

This is quite a common problem especially in warmer climates, the slower hardener would certainly help but there are other ways to reduce the problem. During curing,  the cross-linking of the resin releases heat, it is normal to notice that a part (especially a thick laminate) gets warm during it’s cure. The exotherm is normally the most prominent in the jug or bucket where the resin is in a large mass and ‘exothermic thermal runaway’ can take place, essentially as the resin gives of heat, if the heat is not dispersed, it heats the resin mass further, which speeds up the cure, which releases more heat and so on. It is this loop that causes the runaway; this will result in incredibly quick curing (literally before your eyes) and huge heat generation, which can lead to noxious fumes and even combustion.

Avoiding a thermal runaway: A large quantity left in a bucket is the most common place for the problem to occur, if you need to mix a large batch of resin it is good practice to divide the batch into a number of smaller containers after mixing this will reduce the bulk mass and reduce the risk, an alternative is to use a large diameter bucket so that the depth of the resin is reduced increasing the exposure to ambient temperature. Where possible it may be preferable to mix the resin in small batches as it is required this will obviously reduce the amount of time that the resin spends in a mixed mass.

High ambient working temperatures will also dramatically increase the likelihood of a thermal runaway; if you are working in an environment above 20ºC special care must be taken to avoid large quantities on mixed resin being left standing.

It is possible when making thick laminates (<8mm) that exotherm can cause problems on the part, this can cause distortion and weakened resin matrix’s, if at very thick laminate is required it is advisable to build the thickness in stages and allow the material to cure between them, peel-ply and/or sanding between stages will ensure good interlaminate strength.

Dealing with a thermal runaway: if you notice signs of a runaway (high temperatures in the bucket) do not attempt to cool the resin, it will defiantly be beyond saving. Take the bucket into a spacious and well ventilated area (outside is ideal) leave the reaction to take place watching that it does not run out of control, do not use water to cool the reaction, this can lead to violent boiling and spitting. In the unlikely even that the resin ignites, a fire blanket is the best way to manage the flame until emergency services arrive CO2, Foam, Chemical powders or sand extinguishing materials are also appropriate, only use water with extreme caution.

After completing a project any spare resin in the bucket should not be left unattended, it should be divided into smaller quantities and placed in a well ventilated area away from any combustible materials.

Paul Statham
Easy Composites / Carbon Mods - Technical

Thanks very much for the advice Guys. Great info. I plan on starting a first light, so should be cooler, and I will dived resin into smaller containers. First time I worked on CF I had a "runaway" in only a 16oz pot that was pretty full. I thought What the hell?