>From an article that I recently read, I understand that while the "sacrificial
anode" effect of the zinc chromate or phosphate is a factor in corrosion
prevention, a VERY large percentage of the corrosion protection comes from the
way that the particles of certain solids (zinc chromate, zinc phosphate, talc,
silica, etc.) in the paint absorb the binding resins and interlock with or
overlap each other, forming an impervious barrier that might be compared to
"layers of overlapping glued shingles."
Corroless in particular makes a big issue of this in their advertising,
explaining how the silica crystals interleaf with each other. I've never used
Corroless, so I can't vouch for it, but at least the basic idea does seem
logical.
Alan
-----Original Message-----
From: Lee Phillips [SMTP:lee_phillips@rccgw.chinalake.navy.mil]
Sent: Tuesday, August 26, 1997 10:51 AM
To: RKiser8375@aol.com; Military Vehicles
Subject: Re: [MV] Painting my M37
Bob,
The primer actually does a couple of things. It promotes adhesion, because the
topcoats are better at looking goo than they are at sticking. Also, in the
case of some of the zinc chromate primers (e.g., PPG DP-40, DP-50), the zinc
chromate actually makes a chemical barrier against corrosion. Also, primers
are often sandable (where sealers aren't) so you can get a smoother finish.
The better primers are epoxy based, (PPG, Deft, and others) which makes them
stick about as well as anything ever could, and also are tougher than nails,
making a great subsurface for the topcoat. Primers are highly recommended.
===
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