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Spontaneous Combustion of Plastic!


Uncle Pete

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Here's a curious one.  Has anybody had this happen?  I got the primer and first coat of sliver on my Lightning...

 

Lightning 8

 

So far, so good.  But the next day I was faced with this....

 

Lightning 10

 

I looks like somebody stubbed out a couple of Woodbines on it.  I have no idea what happened.  Regular Tamiya Extra-Thin glue and Humbrol enamels brushed on, no unusual heat conditions in the workshop while it dried overnight, no solvents laying around for spillage.  (And, just for comparison, the metric ton of Evo Stik holding the lead in the nose didn't affect anything).  I'm really scratching my head over this... Anybody got any ideas?  Does this happen often?  Does it ever happen at all?!  Have I been infested by a new species of plastic gremlin?

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Might be a flaw in the plastic ,air pockets or something like a wrong plastic mix . Weird ,not seen that before.

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Trying to think of a scenario that might explain what happened and a possibility is that if the paint was applied before the extra thin cement had boiled off completely, the volatile vapours may have been trapped under the paint. With nowhere else to go, it could possibly continue dissolving the plastic. I have noticed that the Tamiya Extra Thin doesn't boil off as quickly as MEK, for instance.

It's just a guess really, but it's hard to think of anything else that might explain it.

Cheers,

Mark.

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1 hour ago, Stu_davros said:

Evo stick

Yeah ,sounds good …******* Toluene although I remember an Acetone smell , not used it for years …. The transporter (Toluene/Acetone/whatever) in the glue has run down the bottom of the fuse . vapours would do it ,doesn't need to be the liquid

Edited by bzn20
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I'd agree that it was something in the Evo Stick that has reacted.  I remember a similar softening of the plastic in a kit I made years ago after putting too much glue in.  It went all soft and like leather - stayed that way for ages too.  You can find the data sheet for it here, and there's Acetone and Xylene in it, so it'll melt plastic, given the right quantities.  Some probably dribbled downhill into the fuel pack and settled there. :S

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I have had something a bit similar to this happen on my vacformed Dalek, I used some tube glue and the plastic absorbed the solvent in the glue and became soft and leathery like Mike describes and it took many weeks for the plastic the re-harden. So basically some sort of solvent from somewhere has got into the plastic and plasticised it. (It does seam odd / puzzling where this could have come from). Once it does harden the defects should be treatable with filler (probably Milliput) and repaint from there.

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3 hours ago, Stu_davros said:

Evo stick

 

1 hour ago, bzn20 said:

Toluene

 

1 hour ago, Mike said:

Evo Stick

That seems to be the consensus.  I'd ruled it out because the nose itself is OK and a couple of inches away from the damage.  I see what you mean about the vapours, though, they wouldn't be choosy where they went.  I think future nose weights will have to be applied with epoxy.  I only dumped the Evo Stik on heavily because I'd forgotten to put the weight in and had to drill a hole in the nose and shove little splinters of lead through it, chasing them with gobs of glue so they wouldn't wander.

 

4 hours ago, lasermonkey said:

paint was applied before the extra thin cement had boiled off completely

That seems reasonable but I believe it was several hours between glue and paint.

 

27 minutes ago, Nigel Heath said:

the defects should be treatable with filler

I gave it the Miliput immediately.  Lots of sanding involved so the panel lines on the underside are history.  I may have done that too soon... I thought I'd brought it up to level but when I sanded it, it seemed to have dropped in a bit.  Hadn't occurred to me the plastic might still be soft.  

 

This kite is giving me no end of headache and it's not even the right scale (it's a 1/100 and I'm a 72 man).  I'm only carrying on out of obstinacy now!

 

Thanks again, everybody, for all the help.  I don't know what I'd do without the expertise I find here... Probably take up stamp collecting!

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