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

Hia, thanks for the reply, I fear it's too late to recover the peice, a second inspection with fresh eyes reveals that my exuberance with the heat gun has melted parts of the wing, ruining the airfoil. I think this one goes down in the "lesson learned" book. Good idea about the heated bed blanket, it should just about fit underneath (2 meter wingspan). I think next time I'll do it indoors and not in the garage, at least the process is clean, I hate doing wet layups .

Oh nooo... I had the same issue 3 days ago! wish this post was already up! fortunatly i wasn't doing anything as big as that so I feel your pain. it was just an angled bracket thing but it was seriously slow, the penny never dropped that the cold would change the viscosity that much! plus it took about 2 days for the resin to cure, it's still a bit floppy now! I thought I had a bad batch of resin or was using the laminating one! I might build a warm box with a small heater and some kingspan insulation, one of my freinds did one for when he had done a repair on his jetski, I can see why now!

What does everyone think To the idea of a fan heater in a box about 1m x 1m x1m, I don't really like the idea of anything that could catch fire, but I guess if i leave plenty of space around it and maybe put a desk fan in too to stir it up some more it should be fine, they have thermostats built in so it wouldn't ever get over 30deg anyway. I think it would be cheaper that trying to heat my whole shed!

If you going to out it in a box I would make a hole in the back the size of the outlet of the heater, at the opposite end of the box to the heater. This will help air exchange and vent moisture if there is a buildup.

I Agree with CJ on the getting some ventilation in the box, should make it a fair bit safer, your shed is'nt too close to the house if it all goes wrong is it?!!!

I have run a very similar sounding stack to yours CJ as I've just started down the infusion route for wing skinning, after a few small experiments I have gone for this stack;

Bag
Mesh
2x Peel Ply (explain later)
1x perforated release film
3x 25gsm Cloth
Styrofoam
3x 25gsm Cloth
1x perforated release film
2x Peel Ply
Mesh
Bag

I use release film as the last layer contacting the reinforcement as I discovered peel-ply was difficult to remove from the really light cloth, it just kept trying to delaminate and peel it apart, the release film comes of really easily though and leaves a pretty good finish straight away, the 2 layers of peel ply are to smooth out the impression from the mesh a bit, you can run the infusion with 1 or none no problem but the shape of the mesh presses the surface and leaves a pattern the 2 layers of peel ply have helps this a lot.

as for the spiral, so far I've only been doing 6inch wide sections of wing to tests a few methods but i have been pulls the resin from a spiral an inch in front of the leading edge to the vacuum and inch behing the trailing edge, on a 10inch chord wing so a foot in total, this has run through in about 5-10 mins no trouble.

Good tip on the paint powder too I might have to give that a try.

There is an art, or rather a knack to flying.  The knack lies in learning how to throw yourself at the ground and miss.  ~Douglas Adams, Hitchhikers Guide to the Galaxy

Thanks for the tips on the release film and peel ply, I don't pull a full vacuum when I do my foam as I've found on bigger pieces that the foam collapses, I'll pull the mould at full vac (my pump goes down to 30 inmg according to my catch pot) and infuse, then drop the vac to 20-25 inmg to ease the strain on the foam, the pressure is still there (can't remember how many PSI it is) but it prevents the impression of the mesh in my case. Seems to work well anyways. Glad I'm not the only one sandwiching the peice like this, are you gluing the glass to the foam first? Or you just layering it on piece by piece, pulling the vac and hoping it clings straight?

Hi CJ,

No I'm not on RC groups, good tip on dropping the vac a little, I'll give that a go on the next run... i've been tacking the glass cloth in place with a few spots of superglue to hold it straight... seems to do the trick.

There is an art, or rather a knack to flying.  The knack lies in learning how to throw yourself at the ground and miss.  ~Douglas Adams, Hitchhikers Guide to the Galaxy