DANGER epoxy fire!!

[Zippiot]

My buddy decided to fix his windsurfing gear, I usually do the glasswork but he wanted to this time. I use general purpose grade epoxy from tap plastics, 1 to 1 ratio. He used marine grade 4 to 1 ratio (1 part hardener to 4 parts epoxy) but since I taught him to do repairs and had only used my epoxy, he didnt realize the danger.

Hell I had no idea...

He mixed the 4 to 1 in a 1 to 1, it caught fire after about an hour and scorched the area. He was more amazed than bummed, no real damage as the only affected area was the part we were reglassing. Just wiped it off and tried again


Anyone else ever have an epoxy fire?

[Irvine.J]

Not personally, however a mate of mine was doing some work on his boat...
He filled a cavity behind the fridge with hard foam sheets to protect it/stop it banging. He then filled the cavities left with expanding foam filler aka polyurethane filler. After he filled the cavities with the expanding foam, he went to use his power drill and screw in some brakets to hold the cables behind the fridge... He was lying down, behind a fridge, no way to escape quickly... the spark from the INSIDE OF THE POWER DRILL ignited the fumes eminating from the filler! Apparently the fireball was like a mini explosion setting his hair, beard, and brows on fire! In his words "It was alot quicker then shaving and far more painful..."
Ahh the joys of DIY adventures :D

[Dang911]

Yes, I have has a bad experience with epoxy. I was gluing two wings together on a 1/4 scale plane. I was using my favorite 30 min epoxy. I mixed a rather larger batch than normal (1/4 cup) because this was a big job, (still relatively small compared to a real glassing job). I was mixing it an my normal red plastic drinking cups as I always did, 1:1. I mixed it thoroughly, and all looked good. Then it stated to thin itself out. At that point, I kept working, because I had already started and really couldn't turn back. Then I felt the cup getting hot, and I looked at my timer and it had only been 8 min. The mixture kept getting hotter and hotter, and thinner till it was practically water. It finally got to the point where the cup was to hot to handle. I kept working, and the cup started to melt. Steam/smoke started to arise from the epoxy in the cup. I slapped on as much epoxy as I could over the joint and laid the reinforcing glass. I did such a sucky half ass job. At min 11, it was hard as a rock in the cup, yet still tacky on the work surface (normal). What wasn't normal, where the hell did the rest of my 19 min go AND I now had 2 blisters on my hand from 2nd degree burns, and this disaster almost ruined my plane. They were both brand new bottles, and measured exactly. I was furious and went to the epoxy company. This almost cost me a 1/4 scale plane! They gave me some free epoxy, but to this day I don't know what went wrong.

On a normal cure, epoxy will gets warm, even a little, hot, but never to where you will burn yourself.

[Ray]

The epoxy reaction is an exothermic one, as you have found out.

Nothing went wrong, the faster curing epoxies will naturally generate the heat in a shorter period of time. When you concentrate the heat by placing it in a cup or "confined area" it will heat much faster, there just isn't the surface area to dissipate it. When you mix large amounts of epoxy, do it on a plate. You'll get the open time you expect and it won't catch fire.

[MJD]

My buddy decided to fix his windsurfing gear, I usually do the glasswork but he wanted to this time. I use general purpose grade epoxy from tap plastics, 1 to 1 ratio. He used marine grade 4 to 1 ratio (1 part hardener to 4 parts epoxy) but since I taught him to do repairs and had only used my epoxy, he didnt realize the danger.

Hell I had no idea...

He mixed the 4 to 1 in a 1 to 1, it caught fire after about an hour and scorched the area. He was more amazed than bummed, no real damage as the only affected area was the part we were reglassing. Just wiped it off and tried again


Anyone else ever have an epoxy fire?

1. When using epoxies, use the ratio prescribed and don't modify it. Epoxy curatives are just that, curatives, they are not catalysts. Epoxies cure by a polyaddition reaction, where the number of reactive sites on the resin molecules are matched with a similar number of reactive sites on the curative molecules. You can go a little to either side of ideal without ill effects, but stay as close as possible in order to maintain the physical properties of the cured material. To alter the cure rate of an epoxy sytem, you need to change curatives to a more or less reactive system.

This is contrast to polyesters and vinyl esters, which use a catalyst (typically MEKP, methyl ethyl ketone peroxide) to trigger homopolymerization. In these cases some manipulation of the cure rate can be made by small changes in the amount of catalyst, plus there are promoters and retardants that can be formulated into the system.

2. As already pointed out, the cure reaction is exothermic. If you mix a large batch of a reactive system, it will get stinking hot. If you get a chance to look at the manufacturer's data sheet for raw epoxy resins, there is sometimes a figure quoted for the peak temperature during cure, when mixed in a certain batch size and with a standard curative (IIRC, diethylene triamine) - these temperatures can exceed 500F.

If you have a 5, 10, or 30 minute system, mix small amounts. If you are mixing a lot, use only slow systems, such as 24 hour.

The cure rate of an epoxy is dependent on the temperature, which makes it highly dependent on the application - if you spread it out into a thin film (called a "thin film" in the industry, not surprisingly) it has virtually no chance to self-heat through exotherm and will cure at a rate completely dependent on the temperature of the substrates or ambient temperature, whichever is the dominant factor. In contrast, when you have more mass in one spot, the exotherm can raise the local temperature of the material and speed the cure. You just found this out in graphic fashion.

Becasue of this, remember that the terms "5 minute" and "30 minute" are to be taken with a grain of salt, in the knowledge that these times are for typical applications, and can be greatly shortened or hastened by the local conditions.

When in doubt use a slower system, then if it all works out and the cure is dismally slow and the resin has not kicked off before you applied it, use a faster system next time. And exercise moderation in the size of the batch you mix. You can often do the same job with a faster system by mixing smaller amounts at a time - when you feel it warming up, ditch it and make more.

MJD

[Zippiot]

I called him again today and got the measurements of the are he patched. I use a palte when mixing more than a 1/4 cup but otherwize I use non-waxed paper cups. Waxed ones always steam even in small apps.

The area he patched was roughly

1 cm deep and a 8 x 10 inch area. He hit a rock and sanded it down so that no damaged glass was left then filled in the area. Standard stuff. When I onced mixed 4 to 1 in a 2 to 1 it just didnt dry, never got very hot.

I love vinyl ester resins, shrinkage in your project is always a bonus!!!!!!