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Old 07-30-09, 10:50 AM
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Originally Posted by Falanx View Post
Essentially, [porosity of epoxy and other plastic paints] is a fundamental of polymer chemistry. Even the most rigid, cross-linked, three-dimensional polymer structure effectively terminates in lots of places rather quickly, so what's left holding these ten-thousand molecular weight monsters together is dipole interactions and Van der Waals forces. Essentially, static. Gas molecules, and tiny liquid molecules can elbow their way through with enough head of pressure. That's why beverage bottles have a shelf life.
Except the last sentence about about beverage bottles, it's easy to imagine Tom Baker giving the above as an explanation of why the Tardis isn't working! But yes, that makes perfect sense.

If you get a moment I'd be interested to know what you think of the info for the site for KBS Rust Stop. They claim that:
RustSeal completely seals metal surfaces, blocking all the pores and preventing penetration of moisture, oxygen, and water vapor.
And it's a "Polymeric Isocyanate" according to

I noticed that one of the magazine articles archived on their site claimed that an angle grinder was required to remove this stuff, and even that had problems. It's designed to be used as the middle layer layer of a 3 layer sandwich, btw.

[The best combination would be] would be.. (etch primer if it needs it), strontium/potassium-zinc epoxy primer, topcoat. Yep.

You want maximum toughness, I'd say polyurethane topcoat and a good sacrificial epoxy primer. I had to get a Mil Spec PU paint off once. It took a oxy-propane torch and glass bead blasting. No joke. Two HOURS. But it's once again, all down to the prep. You make sure the subsrate is clean and keyed, you take your time with the primer and then you key it again, unless you're handy with putting down a final powder layer on the primer. Be aware that the two are partially mutually exclusive. A wet-coat car paint is real easy to use, but not particularly hardwearing by comparison. A PU paint is a bit of a pig to clean up and strip out of spray tools, but it won't come off, and the chemically resistant nature as a paint is reflected in its behaviour as a film coating.
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