On 20/12/13 14:43, dpb wrote:
On 12/19/2013 6:13 PM, DoN. Nichols wrote:
On 2013-12-18, Larry wrote:
On 18 Dec 2013 04:53:45 GMT, "DoN.
wrote:

[ ... ]

And I've never seen a label on the paint warning about shaking
it, but I *have* seen such a warning label about aluminum paint on a
paint shaker bolted to a vertical floor-to-ceiling I-beam at work (a
later job) This was one of the kind which cranks two flat plates
down on
each end of the can and shakes it around a horizontal axis through the
middle of the can half way between the two ends.

Do you recall what it said? What type of warning was it? Mess or
explosion?

Just "Do not use to shake aluminum paint!" (in big red letters,
IIRC. :-)

[ ... ]

I'd like to see a real explanation--a quick search on manufacturers'
sites didn't bring anything to light.

I would too. But the one about the "tung oil" makes a certain
amount of sense.

Totally different conditions and reaction than whatever's going on (if
anything) in the can.

I know people who have had smoldering fires from catalyzing oil finish
rags, so it's not just hearsay. I dry mine on the sidewalk for a week
before putting them in a trash can. Why take chances? When they're
hard, they're safe. Wet and crumpled, they get hot to the touch. My
first clue was picking up a hot rag in a cold shop. That brought the
warning home to me.

I've always believed the warnings I learned in elementary school
science class, but I've not worked with those materials. I tend to also
put oily rags in a metal trash can, not a plastic one. :-)

My two favorite wood finishes, Watco and Waterlox, are both catalyzing
oils and prone to that.

O.K. So the remaining question is:f

"How hot can a half-full can of this get if shaken?"
...

_IFF_ (the proverbial "big if") this is actually occurring (of which
I'm still not convinced there's not something else at play) I doubt
it's actually much temperature related (at least from internally
generated heat; the hypothesis of starting w/ something hot from
exposure to sun or the like aside)at all but some sort of outgassing
or the like that's generating the internal pressure rise with some
modicum of additional heat perhaps. If this were such a major issue
it seems the cans would have all sorts of warnings and it wouldn't
need just a handwritten sign on the mixer at the local co-op.
I posted the warning message printed on the lid of some cold galvanising
paint I have, it would be difficult to miss when opening, on the 20th
and it said not to shake and also that pressure build can arise due to
moisture contamination. I wonder if the zinc reacts with the moisture to
produce some zinc compound and hydrogen resulting in a pressure build up
in the can.


On the tales of spontaneous combustion, HS chemistry teacher used a
rag to wipe some spill from the lab counter after a demonstration in
last class period of day class and hung the rag on a clothes hook and
closed the door in a small closet. Next morning the door was heavily
charred in the area and the rag was mostly ash on the floor.
Fortunately, it appeared that lack of O2 in the small closet prevented
full-fledged fire. He purposely never let maintenance repair the door
as a reminder both to himself and students...was pretty effective
teaching aid. I, also, to this day, am certain to not leave finishing
rags in precarious places.

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