Holy CA Batman... CA+Balsa = FIRE!!

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Salvage-1

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Has anyone else had this problem??

I was working on a set of balsa fins. Sanded them down and gave them a wipe, then got the "SuperThin" CA out and started painting the balsa.
A couple of seconds into the paint, I started to see bubbles forming on the surface of the balsa, then smoke, then a little discoloration, then... a pop sound and the balsa caught fire.
For a couple of seconds ehe fire was almost as if the balsa was soaked in gasoline, it was burning on the surface, then the discoloration spread and I could see the balsa was burning.

I dumped a CO2 extinguisher over it, which froze the balsa and caused it to shatter when I picked it up, although there wasnt much of the fin left anyhow.

What happened?? Anyone have a clue? Has anyone else had this happen to them?
 
Moisture in the balsa, maybe. Would tend to kick the CA and cause it to cure more quickly. CA heats up when it cures, especially the thin stuff. I can easily see it getting hot enough to ignite extra-soft wood.
 
You said that before the CA, you "gave the fins a wipe". What did you use?
If it was accelerant, or something like it, I'm not surprised. CA heats up when it cures, and it really heats up if you use accelerant. Enough to ignite balsa, apparently. It's normal for it to smoke a bit when it flashes off, but I've never had it actually catch fire myself.

Anywho, glad no one got hurt and nothing damaged (other than the fin). Be careful out there!

s6
 
Moisture in the balsa, maybe. Would tend to kick the CA and cause it to cure more quickly. CA heats up when it cures, especially the thin stuff. I can easily see it getting hot enough to ignite extra-soft wood.
You said that before the CA, you "gave the fins a wipe". What did you use?
....

s6


I just grabbed one of my 'scrap rags'. Standard old cotton T shirt that has been re-purposed. I keep a bunch of them around for rocketry, wipe down after sanding, etc., etc
So, yes, it could have had a small amount of moisture on it from somewhere. I keep the rags that I use for other stuff (denatured alcohol, oil, etc) in separate bins so they don't get mixed, and they all get through the laundry regularly, so I doubt if anything else would have been transferred.
This wipe was an 'after sanding' to get the sawdust out of the grain.
 
Yes, I have seen a little smoke previously when I have CA's balsa, but I thought that was just the curing!
 
At home in the PNW, where it's more humid, I like to drip thin CA into balled up tissues and light them on fire...

CA is accelerated by moisture, but that's not what makes it cure. The curing process is kinetically driven-when you press the liquid into a thin film, it reconfigures molecularly. This gives off large quantities of heat. In porous media where capillary action is a big thing, it spreads into a thin film on its own, giving off more heat all of a sudden.

At least that's what I remember reading, once upon a time, researching it for USLI.
 
Back in the day we used baking soda to make CA fillets on timer and fuse fittings on free-flight gliders. You spread some soda on the line you want to fillet, shape it lightly with your finger, and then put a drop of CA on end end and watch capillary action soak its way through the powder. The end result was hard as a rock and would glue anything to anything.

One time I tried the same technique on a larger scale. I had two pieces of 2x4 that needed quick and dirty joining on their flat sides, and balking soda wasn't going to work since the fillet had to be so much thicker (CA hardens before it can penetrate a thick layer of powder, and you end up with a thin crust on top of free powder). So I got the bright idea to use sawdust as filler material and CA as binding agent.

I suspect if the pieces were smaller than 2x4, they would have caught on fire. As it was, I got lots of smoke and charring, but ultimately no fire. It did get pretty exciting, and I keep a fire extinguisher in the shop now. When the assembly cooled though, the shavings were hard as a rock and I could not separate the pieces with a hammer.

Ari.
 
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