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I'm not a chemist (and I don't like Holiday Inn Express) but I did work in a
chem lab for a while making experimental batteries for electric cars. We
used acetone rather freely, and I'm pretty sure that acetone gives me a
powerful headache. (MC on the other hand, just gives me liver
cancer....which I don't really have because I treat MC like it's poison.)
Anyway, I use MC exclusively because it's a superior solvent. Just smear
some schmutz on a piece of anything with a shiny surface, or glass, anything
on which you can plainly see if the residue is there. Squirt some acetone on
it and watch the schmutz kinda dissolve -- squirt some MC on it instead and
watch the schmutz just instantly disappear. Like David Jones, I sometimes am
frustrated by people ignoring my advice, but on this issue my first-hand
experience confirms his wisdom.
I've discovered that some shops don't use MC because of the OSHA regulations
for personnel protection required for MC that aren't required for acetone, or
so they tell me. Kinda makes you wonder how safe it is to use at home, eh?
And if you read the MSDS you'll see that the TLV (threshhold limit value --
maximum concentration allowed for 8 hours continuous exposure) is exceeded by
one drop evaporating in a standard size garage. But I don't have MC floating
around my shop for eight hours per day. I only use it just before a layup,
and then I air out the shop.
How do I, a non-expert and non-chemist, protect myself? I have a small
bottle of the stuff, so that the risk of spilling is significantly reduced.
I refill the small bottle from a larger bottle when I need to. I refill the
larger bottle from my 5 gallon can outdoors -- I spill a lot here. (It kills
grass, by the way, but that's another story...) I try real hard not to
breathe the vapors when I'm wiping things down or refilling bottles, and I
open the garage doors when I am wiping. I throw the dirty-but-still-wet rags
outside to dry. I wear the heavy gloves (butyl) for wiping. Even though
these gloves are too heavy for precise work, they're okay for wiping. I then
don't touch the parts unless I'm wearing latex gloves. It's not as much
protection as the chemical fume hoods in the chem labs, but it seems to be
working for me. No liver cancer yet (I hope....)
I prepare surfaces a little differently than Curtis. I agree with him that
roughing up a surface within an hour of bonding is good -- and my chemist
friends tell me that the surface is more "chemically active" that way and you
get a better bond. The difference is that I wipe off the dust -- and any
residue that I've inadvertently applied with the sandpaper -- with MC before
bonding. Also, I clean before sanding as well because, as the manual says,
it's kinda dumb to grind any dirt or oil into the surface with sandpaper --
better to clean it off first.
With respect to Steve Colwell's comments -- you can definitely get solvent
soaked into a honeycomb or foam core, and that's stuff's gonna come out
somewhere. Better to wipe down those surfaces some time prior to bonding to
give time for evaporation and vapor escape, and a heat gun definitely helps
here.
I'm told by an ex-Lancair employee (from the Philippine factory) that they
did run adhesion tests with acetone-prepared surfaces, and that adhesion was
improved by letting an acetone-prepared surface "dry" overnight. Take that
as an unconfirmed rumor.
I know a lot of airplanes have been successfully built with acetone as a
cleaner, but I'm sticking with MC.
If you have problems finding MC, call the oil companies (like Shell Oil, for
instance). Not the gas station at the corner, but in the Yellow Pages -- the
distributors. It turns out that MC is a by-product of the petrochemical
industry, or is used meaviny by them, or something, because you can get 5
gallons for around $35, and if you buy gas chromatograph grade stuff from,
say, Fisher Scientific it costs about $80 per gallon.
(Marv has a list of MC suppliers somewhere on his website, by the way.)
- Rob Wolf
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Please send your photos and drawings to marvkaye@olsusa.com.
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