Elliot wrote:Without bothering to investigate.... This is almost certainly simply good old fashioned Phosphoric Acid,...
Nope. Penetrol isn't that.
It's not a rust remover
. Use it as a rust treatment paint. Think of it as Tremclad rust treatment paint, only it works, and lasts. Negative is you have to give it cure time before you topcoat
, if you want a topcoat. Well, not quite like Tremclad; no colour and I haven't tried adding a pigment to it. No need. Easily top coated.
But I used to use phosphoric acid based rust removers. Now I use evapo-rust. Even reconditioned suspension springs with it. Horribly expensive, but works well. But I find it often takes more time that their directions say.
Elliot wrote:Hmmmm... indeed. ... -- reminiscent of WD-40. Or am I on the wrong track all over again? ...
Good guess, but thankfully nothing like WD-40.
This dries to a hard finish, like linseed oil and tun oil and other "drying oils" correctly applied to wood. Pre-polymerized means you're not waiting weeks for a cure.
Bob wrote:Penetrol MSDS
Ingredients: medium aliphatic solvent naphtha; polymerized linseed oil; stoddard solvent (mineral spirits); soya long oil alkyd resin; proprietary blend of heat polymerized linseed oil
Made with drying oils.
They dry by the solvent evaporating. Then they cure by bonding with oxygen. In between the two, you have a period where they can polymerize.
After the solvent is gone, the coat is obviously thinner on the applied surface. But, as it's largely a drying oil, as it polymerizes, it also shrinks/skins-down into a thinner coat. Think skin-tight.
The great part is that the polymers of linseed oil link together (and possibly cross-link), then they cure by bonding with oxygen into polymers of linoxyn. So when applied to rust, it coats and soaks in, then cures. The O2 bonding removes O2 under the coating from being available for rusting. As neither oxygen or water vapour can get under the coating, further rusting is limited to what oxygen is in the metal - in practical terms, naught. I suspect the oils also absorb and encase salts that may be mechanically present in the oxides, thereby removing them from being available from promoting rust. Same for any dirt you didn't get off: Penetrol soaks through and encases it, so it can't absorb water (which can hold O2 and salts) and hold it next to the metal - recommended method is to remove dirt first, but...
Some day I'm going to try it as a replacement for my various pure oil & blends based on tung oil or linseed oil for my wood projects. But what I have works very well, so I have to wait for a project that doesn't matter much. Would sure be less expensive than the fancy "pure" products that I'm using now for wood projects.