Exploding Shellac?

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I had a small can of shellac (half pint) with a press on (not screw-on) lid, sitting on a basement shelf. Today I noticed a wet floor, though the toilet leaked. They saw the can on its side, the bottom buckled as if pressure built up inside, finnally exploding the can open, and pouring itself on my floor.
WTF?? Is this 'normal'? Anything else down there ready to explode?
JOE
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Anything else with relatively high vapor pressure that you put away cold and allow to heat up. That's one reason for screw-on lids.
Never left a bit of cold soda in the bottom of the bottle and closed the windows on the pickup?
Don't open it near anything you care for.
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George wrote:

It's been sitting there 8 years. Basement temp is stable. I avoided the garage figuring the temp extremes would be bad for paint, solvents, etc. Thought metal cans in basement were safe. But thanks for the reply. I'll be more careful. JOE
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8 year old shellac is garbage....
David.
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George wrote:

Yeah, well...I just went out to my little pick-up and found the damned rear view mirror (with two overly heavy map lights) hanging by its wires.
This heat is a real joy. We go years barely seeing 90, and this year, I think we've had at least 10 days well into the 90s, most of them mid or high. Pfui.
I'll have to drive the dangler into town, get glue, scrape and clean and reinstall.
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Charlie,
Having had to do this several times - I found out what was causing it on mine at least. Obviously the high temp of the two dissimilar materials - glass and metal but the main reason was that the mirror base was not flat and even had a small, sharp bump in the casting. I did the Scary Harp routine on it, cleaned the glass and base with alcohol then applied some standard CA (super glue) and that mirror hasn't budged. The car is in Fla now with my mother-in-law and its still attached. So look at the base closely.
Bob S.

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BobS wrote:

Back in '74 I brought a brand new Falcon. A bout 4 weeks after purchase I took my Girl Friend (Now Wife) to the drive in. Had a mate and his sheila in the back seat. Very proud of my new shiny red car. Set the car up on the hump, and reached up to move the mirror out of the way so those in the back seat could see. Yep ended up with the whole bloody thing in my hand. Major embarrassment. Took the car back to Ford, as it was under warranty and had the mirror re fixed. A couple of weeks later found the mirror laying on the front seat. Took the car back to dealer, had it fixed. A while later while driving the bloody thing fell of again. Took the mount of, mixed some 2 part epoxy, jammed it in place with a piece of 2 x 1 from the rear seat to windscreen until dry. That mirror never came of again. Regards John
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The sharp bump at the base is actually intended. Provides a bit of stand off, such that there will be (has to be) a thickish layer of glue. A thin layer of glue cannot handle the stress due to expansion differences between mirror base and window as temperature swings. A thick layer can.
Theo

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Theo Veenstra wrote:

Mine slips into a plastic boot that I presume is supposed to handle the expansion problem. CA glue is not supposed to be applied thick, the design you describe was probably intended to use RTV.
--

FF


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On Thu, 04 Aug 2005 00:36:07 +0000, BobS wrote:

I had a similar problem with my Beretta. I finally used some sandpaper to rough up the glass a bit before reattaching. Worked great.
--
-Joe Wells

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That ain't heat... :)

A'yup! The older I get, the less I enjoy two of the four seasons...
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wrote:

I'd love to see some 90's!!!! Last night it actually got to about 92 in the shop by 10pm... Of course, I did have 3 BIG fans going... I also ran a DC hose up to the peak of the ceiling and took the hose off the bags and shoved it out a window... running it for about 20 min. brought the temp down almost 5 degrees.. lol
The things we'll do to be able to make shavings and saw dust constantly amaze me..
mac
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Charlie... they don't glue them any more... I had one that I re-glued twice, with the special little kits they sell, and it failed both times within one summer... The new kits have a pre-cut slice of some really sticky stuff that seems to work much better.. YMMV
mac
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Anything that was colder or at lower pressure when sealed..
I learned the hard way that you don't put a new can of coffee in the RV at 300 feet and open it at 11,000 feet... we've been finding coffee grounds in the trailer for over a year.. lol
mac
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mac davis wrote:

I don't mean to be dense about this but;
The can was untouched for years, 7-8 my guess. My basement is 65 in winter, maybe 75 in summer. I should have trashed it 5 years ago.
I have gallon cans of poly, will I have the same issue?
I understand the solvent soaked rag issue, I leave those out in the yard to dry and throw out. My real question is, was there something unstable that caused this? And what else might blow up? No fire, but this small can made quite the mess.
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sort of a mystery to me, also... the rag issue needs air to happen, so unless air suddenly got in after all those years, that wouldn't be it..
mac
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JoeTaxpayer wrote:

According to Bob Flexner's book _Understanding Wood Finishes_ shellac is acidic and shellac cans are coated to prevent corrosion. So maybe after eight years or so the coating broke down and the corrosion generated enough gas, hydrogen I would think, to overpressure the can and pop it.
What is the condition of the inside of the can?
--

FF


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snipped-for-privacy@spamcop.net wrote:

It didn't seem unusual on the inside, coating looked ok. Can did have warning that it might not be good after three years but no explosion warning.
My question remains - will Poly have the same issue? I have a new, half used gallon can, I thought I'd keep till the next project. JOE
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On Thu, 04 Aug 2005 19:19:51 -0400, JoeTaxpayer

Shellac is a natural, organic product. It is quite possible that if it was a partial can there had been some contamination introduced at some point that allowed bacteria to grow and eventually produce the pressure and explosion. About the only thing I can think of.
-- "We need to make a sacrifice to the gods, find me a young virgin... oh, and bring something to kill"
Tim Douglass
http://www.DouglassClan.com
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Crossposted to sci.chem.coatings where maybe there is someone who will know the answer.
Tim Douglass wrote:

OIL soaked rags, in particular boiled linseed oil and tung oil or opther _drying_ oils, that is those that react with oxygen and polimerize as a serious spontaneous combustion hazard as the process is exothermic and the material is combustible. Solvent- soaked rags should also not be kept indoors (for the most part, not _used_ indoors either) both because of the danger of developing an explosive atmosphere and for to minimise exposure.

I thought of that too, but the bacteria in question would have to survive in a mixture with a high concentration of alcohol. There are bacteria that do that, they can even contaminate the alcohol used in hospitals.
Alcohol is an organic base, shellac an organic acid the reason pre-mixed shellac has a short shelf life is that they react, degrading the shellac. I think this is the process known as 'aponification'. Does that produce gas?
--

FF


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