How good is good enough, DAPO? Options

[930cabman]

Given this former Cali car is coming up on 50 years and probably not always taken good care of, I am lucky to have this level or rusting. I went after it with Ospho, wire brush and clean rinse.



Will be applying POR 15 to this area.

Question: my gut tells me the well adhered tar is sound and is not hiding any rusting.

[Superhawk996]

More devils advocate:

IMHO POR 15 has its uses.

Low buck, low quality, heavily rusted stuff you don’t care about too much but where you are wanting it painted is where I tend to use it.

POR15 is a moisture cure urethane product largely for Paint Over Rust (POR) as the name implies. It depends on the adhesion of the rust to iron to form its bond to metal while sealing the rust underneath. It does not stop rust under that coating despite what is implied.

When used on bare metal, it doesn’t form as strong of a bond as epoxy primer. The instances of POR15 peeling off in sheets from bare metal (smooth or sandblasted) are well documented. This always gets blamed on prep, but is the nature of the beast (moisture cure) paint which was not designed to be used as “primer”. Likewise, once cured, other paints don’t like to bond to POR15. And per the POR literature, POR15 isn’t UV stable so it needs to be topcoated if exposed to UV. But . . . Other paint doesn’t stick well to it . . . So there’s that little problem.

I don’t think highly of POR15, but have used it on occasion, I thought I’d outline why it isn’t the right product to use for OP’s proposed purpose.