Why aluminum paint?

Bob Engelhardt fired this volley in news: snipped-for-privacy@news4.newsguy.com:

The primary reason it was first made (besides the 'fake metal' look) was because originally, paints were made with natural drying oil vehicles (varnishes-- tung, linseed) which were VERY suseptible to UV damage by sunlight. Aluminum, better than any other pigment available, positively blocked the UV.

It also looks nice, to paint a piece of metal that _should_be_ silvery, but's all corroded, and get it back to looking like clean(ish) metal again.

LLoyd

Steam radiators were painted with it.

Oh, yeah - I've had some of those.

The original thinking was, I think, that it would radiate heat better. Then they found that what it actually did was reflect heat back into the radiator, or something like that. Whatever the reason, they found that aluminum was a very poor choice and "cream" colored (?) was best. And that you had to remove the aluminum paint before repainting. I don't imagine that many people did that.

All in all, I think that using the aluminum paint seemed like a good idea, but nobody actually tested it. Happens a lot.

Bob

In the southwestern US flat roofs are often painted with it. Art

Look UP. Got any metal flashing that's been painted? That's essentially the only place we used the stuff.

Aluminum paint is for playing the Tin Man in the school play. Sheesh! I thought everybody knew this. Eric

Makes a good stain blocker on knots. A coat of aluminum paint, then prime and paint as normal. No bleed-through.

Well, that's a good enough reason to have a can around. Bleed through drives me crazy. I usually treat the knots with 2 coats of shellac, a coat of Kilz, then prime & top coat. And cross my fingers.

Thanks for the tip, Bob

Old time house painters would use a coat of silver to cover very dark color of paint when they wanted to paint over with a lighter color. The aluminum has superior coverage and a neutral shade.

Paul K. Dickman

It makes a very good, light weight UV blocker. As used on fabric covered wings. Aluminum dust mixed in the clear dope.

Paint house metal flashing - fireplace ? Other outdoor metal protection and looks. They have cold zinc also.

Mart>

Primer sticks to it?!?

always has for me - I guess it might depend on the primer - and the "aluminum paint"

But there is also something to beware of with that -- and something which is likely to happen given how long it has been sitting in your house.

*Don't* put it in one of those paint shakers to get it stirred up and properly mixed. A friend worked for a while in a hardware store, and someone else put a can in the paint shaker (ignoring the warning labels to not do that on the shaker) and after a few minutes the can blew up, spraying the hot aluminum paint all over the store. :-)

Apparently, the friction of the flakes of aluminum developed a lot of heat compared to other pigments. And maybe, once it got hot enough, the pigment and the vehicle may have reacted together.

Stirring an open can with a bent shaft in an electric drill apparently does not generate anything like this amount of heat, so you can do that.

Enjoy, DoN.

"DoN. Nichols" fired this volley in news: snipped-for-privacy@Katana.d-and-d.com:

Actually, that's not a problem with a full can, nor particularly with modern synthetic vehicles.

Boiled linseed oil and boiled tung oil are "drying oils". That's a misnomer, because what they actually do is not 'dry', but 'cure' with the oxygen in the air, once exposed. The only thing that dries in that sort of paint is the extra solvent added to get it to proper consistency for brushing or spraying.

To that end, as the oils oxidize they do *(like any other material that's oxidizing)* liberate heat.

In a full can of paint, there's not enough free oxygen to particularly warm up a can, and most of it has already been consumed just sitting on the shelf, anyway. The same is true of a partial can that has been sitting for a long while.

However, I don't know anyone who wouldn't first (almost compulsively) open a can before using it -- even before shaking it. You just HAVE to look! (sure... to check it's not skinned over, still good, how much... natch). And when you do that, you refresh the oxygen load in the can.

NOW when you shake it, you may have a small amount of the drying oil and a large amount of air. Shake it, and you literally aerate the oil, encouraging a rapid, heat-generating reaction.

If you get that mass hot enough, you volatilize the solvents, raising the pressure in the can significantly. Worse, because the solvents are dissolved in the oils, when you remove the lid, they may boil off (flash off) from solution, causing the whole contents to erupt from the can.

It's not the aluminum. In fact, if anything, the aluminum would be competing with the oil for the oxygen... but generally doesn't oxidize much, because it's slower to react, and because as soon as it develops an oxide skin, it inerts itself. That said, add water to the mix, and all bets are off. Water, aluminum, and a higher-than-neutral pH can cause some vigorous reactions.

Lloyd

Right, they polymerize.

That they can and do. Watch your rags, they can burst into flame from this process. I dry mine out flat on the sidewalk for a week, then dispose of 'em, usually in the burn pile.

Since the propellant of choice seems to be propane nowadays, I wouldn't be too sure of the safety, Lloyd.

I roll my (unopened) cans to see if they still liquid. Then I shake, and only then do I lift the lid.

Paints and oils shouldn't be shaken just prior to application, but I've never felt any temperature rise from shaking a can of anything. I suppose it's possible, but you couldn't prove it by me. For the catalyzing finishes, I always float argon on the top to eliminate the problem of skinning. Yet another reason to have a little TIG around the shop, wot?

Interestinger and interestinger.

Larry Jaques fired this volley in news: snipped-for-privacy@4ax.com:

non-sequitor, Larry... we're talking about open bulk cans of paint, not spray cans, which NEVER get any free oxygen in them, til you puncture them for disposal.

Yes, oil paints should not be shaken JUST prior to application, but shaking is just fine, so long as you let them de-gas before use, AND you verify there was no 'skin' in the can before you shake (lest little crumbs of that get dispersed into the finish). Flooding a partial can with inert gas before hammering on the lid is a good way to help prevent that.

Neither have I had any paints heat from shaking, but it is possible with a natural vehicle paint, it's just not the aluminum causing the problem; it could happen with any linseed or tung oil paints. As you mentioned, your rags are evidence of that.

Lloyd

On 12/15/2013 9:26 AM, Lloyd E. Sponenburgh wrote: ...

I'd think it _highly_ unlikely the actual "accident" described actually happened for the ascribed reason in the tale...

There's nothing that's _that_ chemically reactive there that simply shaking even with the introduction of atmospheric air is going to initiate that much of a chemical reaction to produce that amount of pressure rise.

dpb fired this volley in news:l8kncu$bt$1 @speranza.aioe.org:

I agree. There's a long stretch between "could happen", and "likely to happen, given real-world conditions."

Part of my business has to do with the "woulda-coulda-shoulda" concerning manufacturing of explosives, and the safety directives to minimize the impacts of those thought-explorations. So, I have to look at extreme possibilities, and mitigate them so far as possible, even if they are not 'practical' concerns.

LLoyd